Pseudomonas

• aerobic gram negative bacilli (aranged as pairs)
• cytochrome oxidase positive
• capable of producing polysacc capsule (mucoid strains)
• ubiquitous: water, soil, plants, animals
• pili, alginate, flagella
• elastases: Las A, B involved in lung injury
• proteases: complement activity
• exoenzymes through type III secretion
• endotoxin (LPS)
• enterotoxin A Type III secretion and important 
• risk patients: cystic fibrosis, mech ventilated, burn patients, immuno compomised and vascular cathetars

Exotoxin A

Pseudomonas

• disrupts protein synthesis by blocking peptide chain elongation
• catalyzes NAD-Dependent ADP ribosylation of EF-2
• same mechanism of action as diptheria toxin
• causes tissue destruction
• type III sec?

Pseudomonas Infection

• pulmonary infection most common
• mild to severe bilat bronchopneumonia
• respiratory colonization is common in hospitalized (diagnostic dilemma cause might be benign)
• high mortality cause of frequent treatment resistance
• burn wound infection, folliculitis (hot tub folliculitis), osteochondritis (foot or ear from puncture), ear (otitis externa, malignant or not), and eye (corneal inf, and vision loss may occur)  
• non malignant otitis externa is swimmers ear
• loves moist environments

Pseudomonas Bacteremia

• most common in immunocompromised hosts: neutropenic patients, diabetes mellitus, burn patients and hematologic malignancies
• common sources: pulmonary, urinary tract, soft tissue sources, indwelling catheters
• endocarditis: IV drug users

Pseudomonas Laboratory Diagnosis

• grows on typical blood and MacConkey agar
• oxidase postive
• non-fermenter
• fruity odor
• colony morphology can vary depending on mucoid production

Pseudomonas antimicrobial resistance

• accumulatse resistance
• common resistance mech: mutation of porin proteins, beta lactamases, cephalosporinases
• includes plasmid and chromosomal encoded resistance
• resistance may develop while on therapy
• multiple drug resistance is common

Burkholderia

• similar to psuedomonas, opportunistic colonizer
• B. cepacia complex most common: cystic fibrosis pts, chronic granulomatous disease, and involves lung lymph skin soft tissue and blood stream
• B. pseudomallei: immunosuppressed, renal insufficiency, diabetes, melioidosis
• treatment: sensitive to trimethoprim-sulfamethroxazole
• the treatment is distinct from pseudomonas, which is resistant to that

Stenotrophomonas maltophilia*

• similar to pseudomonas, passed thru multiple classif
• opportunistic pathogen: impaired immunity most often
• bacteremia and pulmonary infections predominate
• multiple drug resistance is typical: susceptible to trimethoprim-sulfamethoxazole (pseudomonas resistant to it)
• stenotrophomonas is resistant to carbapenems
• he skipped this slide*

Acinetobacter

• opportunistic pathogen, similar to pseudomonas
• gram neg coccobacilli, oxidase negative, strict aerobe
• A. baumannii most common species
• respiratory, wound, UTI infections most common
• risk factor is tx with broad spectrum antimicrobials
• multi drug resistance is a major problem
• therapy guided by susceptibilities

Moraxella

• similar to pseudomonas
• M. catarrhalis is the most important member
• gram negative diplococci
• oxidase positive
• common illnesses: otitis media, sinusitis, pneumonia
• beta lactamase producer (90% of isolates)

Neisseria

microbiology

• non pathogen (n. subflava) and pathogen (gonorrhoeae and meningitidis)
• aerobic, nonmotile, gram negative diplococcus
• oxidase and catalase positive

N. gonorrhoeae

• fastidious, sensitive to drying; no true capsule
• sensitive to temps less than 35C
• CO2 promotes growth
• Human pathogen
• major world prob and reservoir in asymptomatic people (more common in females)
• transmission through various forms of sex
• decline since 1980, peak incidence 15=24 (15-19 women at highest risk)
• males reported more than females

N. meningitidis

• moderately fastidious (not as much as gonorrhoeae) , polysacch capsules (12 serotypes)
• Type A. B, C, W-135, Y are important cause found in diseases
• Type B - poor immunogen
• human pathogen, colonize nasopharynx
• respiratory droplet transmission and close contact and lack of Ab promote disease
• peak occurence 6-24 months of age, adolescents, young adults
• 8% fatality rate 
• outbreaks at military, colleges and child-care
• carrier rate 18% (9.6 months) and adult men 19-39% in nasopharynx
• incubation: 3-7 days

Neisseria

Virulence Mechanisms

• pili (to enter cell), porin proteins (cell entry and resistance to serum bactericidal effects) and opa membrane protein (involved in adherence) (makes it opaque)
• Rmp (reduction modifiable protein): block serum bactericidal activity
• iron acquiring proteins
• IgA1 protease that degrads LAMP1 on lysosomes
• Lipooligosaccharide (LOS), rather than lipopolysach (LPS)

Lipooligosaccharide

(LOS)

• found in neisseria (menigitidis and gonorrhoeae)
• potent endotoxin, much like LPS)
• LOS is similar to LPS: same lipid A moiety but contains oligosacch rather than polysacch O-antigen
• LOS is associated with invasiveness
• LOS provides useful vaccine epitopes

N. gonorrhoeae

Clinical Disease

• uncomplicated urogentical infection
• females: vaginal discharge, dysuria, often asypmtomatic
• males: acute urethritis; often symptomatic
• rectal GC: 40% w/ genital or urogentical infectin
• pharyngeal GC: 10-20% w/ urogenital disease
• disseminated gonococcal infectin: 0.5%, arthritis and dermatitis (rash and joint pain)
• pelvic inflammatory disease (PID): 10-20% of women with GC
• perinatal transmission: opthalmia neonatorum (lots of pus)

N. gonorrhoeae diagnosis

treatment and prevention

• gram stain, culture (organism fragile), Nucleic acid amplification tests (urine/self-collected swabs)
• gram stain of urethral discharge
• third gen cephalosporins, treat suspected co-infections
• management of sexual contact
• neonatal eye prohylaxis
• no protective immunity
• also treat for chlamydia co-infection

N. meningitidis

diseases

• transient bacteremia: fever, malaise (lasts 24-48 hours)
• meningococcemia (no meningitis): rash, sepsis, shock and skin necrosis (in blood)
• meningitis (+/- meningococcemia): meningeal signs/symptoms
• chronic meningoccemia (rare): 2-10 days of rash-may last months

N. meningitidis

Fulminant Meningococcemia

• Neisseria bacteria
• where meningitidis gets into the blood stream and goes all over
• vascular collapse
• multiorgan system failure
• adrenal hemorrhage -waterhouse-friderischen syndrome
• high mortality despite therapy

N. meningitidis Diagnosis

Treatment and Prevention

• cultures: blood, CSF and petechial lesions
• thayer martin media or chocalate
• CSF - gram stain, latex agglutination
• antimicribial therapy (penicillin/treat home) and supportive care 
• meningococcal vaccine: groups A, C, Y and W-135, conjugate vaccine (MenACWY)
• MenCY for infants with high risk (comb Hib-MenCY)
• No vaccine for Group B

Enterobacteriaceae

antigens

• commensal: humans, animals, and environment
• pathogenic adaptations: enteric pathogens (diarrheal disease) and extra intestinal (pneumonia, sepsis, meningitis, and UTI)
• O antigen: outer portion of LPS w/ large variety, useful in identification and assoc btw serotype and clinical disease
• K antigen: capsular: composed of polysacc (ecoli K1, kebsiella and salmonella)
• H antigen (flagella): typically motile (proteus), used in classification and may function in virulence (salmonella)

Enterobacteriaceae

virulence

• typically lactose fermenters but salmonella, shigella and proteus are not
• structure: antiphagocytic, phase variation
• toxins, adherence and invasion factors, and siderophores

Citrobacter

• an enterobacteriaceae
• C. diversus and C. freundii
• opportunist, especially for newborns
• UTI, sepsis and meningitis
• neonatal meningitis: C diversus- 75% develop brain abscess

Proteus mirabilis

• enterobacteriaceae
• flagellated swarmers (will cover plate)
• urease production
• UTI: struvite stones

Enterobacteriaceae

Toxins 

• endotoxin - LPS: TNF, IL-1, fever, DIC, hypotenstion and death
• exotoxins: cytotoxins (nonspec cell injury) and enterotoxins (cell specific, receptor

Escherichia Coli

Urinary Tract Infection (UTI)

• E coli most common cause of UTI: cystitis, pyelonephritis and urosepsis
• uropathogenic strains of E. Coli: associated O serotypes, k antigen may play role and fimbriae(P fimbria) attachment-uroepithelium
• Pap (pilus associated w/ pyelonephritis
• Rod like projection: present in 60% of UTI strains and 50-90% pyelonephritis strains
• adhesion subunit PapG (3 forms - I-III)

Gastroenteritis

general

• enterobacteriaceae
• diarrhea: freq, consis, volume, watery, inflamm.
• fecal-oral transmission
• inoculum: bacterial load req for infection (10¹-10⁸)
• worldwide: 5 million deaths per year (dehydration)
• e coli most common bacterial infection
• sanitatin most common reason
• diarrheagenic e coli  strains: EPEC, ETEC, STEC, EIEC, EAEC

Entopathogenic E. coli

(EPEC)

• enterobacteriaceae that caused diarrhea
• first described, most common world wide
• infantile diarrhea
• protracted secretory (watery) diarrhea
• specific O serotypes (O127)
• complex pathogenic mechanisms
• decreased incidence in developed countries
• attachment: bundle forming pilus (bfp)
• effacement: Type III secretion system, tir (intimin receptor, intimin(eae gene) cytoskeletal chages: actin polymerization

Enterotoxigenic E. Coli

(ETEC)

• diarrheal causing enterobacteriaceae
• colonization fimbriae: mucosal adherence: CFA I-III
• enterotoxins: plasmid encoded: heat labile toxin (L T-1, LT-2) LT-1 in humans; heat stabile toxin (Sta, STb) Sta in humans
• Heat Labile Toxin (LT): related closely to vibrio toxin, one A and five B su, doughnut complex binds GM! ganglioside,
• LT toxin complex endocytosed, A subunit actiavtes adenyl cyclase and increased secretion of Cl-

Enteroinvasive E. Coli

(EIEC)

• low incidence in developed countries
• non lactose fermenters which is weird for ecoli
• similar to shigella: biochemically and pathogenically (invasion of colon epithelium and enterotoxin production)
• lesss severe than shigella: often watery diarrhea

Shigatoxin producing E coli

(STEC)

• bloody diarrhea causing jenterobacteriaceae
• associated w/ hemolytic uremic syndrome
• 3rd or 4th most common foodborne infection in US
• hemorrhagic colitis: little fever, bloody stools, abdominal pain and may be non blood
• hemolytic uremic syndrome (HUS): anemia, renal failure, thrombocytopenia (5% of children less than 10 with 5% mortality)
• serotype O157:H7 most frequent and fails to ferment sorbitol (convenient screen)
• virulence mech adherence and cytotoxins

STEC pathogenesis

• Shigatoxin producing E. coli
• bloody diarrheae causing enterbacteriaceae
• adherence ande effacement (A/E lesion): same as EPEC, uses tir and intimin
• shiga toxin (Stx) I and II: Stx almost equal to toxin of S. dysenteriae type I
• Stx has A, B subunit structure inhibts protein synthesis

Enteroaggregative E. Coli

(EAEC)

• diarrhea causing enterobacteriaceae
• increasing cause of diarrhea worldwide
• adhesins
• toxins being described
• stacked brick appearance on intestinal epithelial cells
• dont know much about it

Shigella

• enterobacteriaceae
• most common cause of infectious diarrhea in USA
• 4 serogroups (dysenteriae, sonnei, flexnerii, boydii
• fecal-oral transmission: low inoculum, human reservoir
• major cause of dysentery: blood, mucus, tenesmus, s. dysenteriae type 1 in developing countries along w/ s. sonnei
• sepsis is rare
• complications (esp s dysenteriae): seizures, hepato urogenital syndrome (HUS), intestial perforation

Shigella

Pathogenesis

• invasiveness - M cells
• invasion plasmid antigen (Ipa A-D) type III
• enter lamina propria
• induce production of IL-1, inflammatory response, loss of tight junctions
• re-entry at basal surface (phagosomes)
• escape phagosomal vesicle and spread to adjacent cells (IcsA, ATPase, polymerization (host cell actin) and propulsion, cell death and focal ulceration (exudation inflammatory cells)
• Shiga toxin (Stx) I, II: identical to Stx I of STEC: cleavs adenine residue from 28S rRNA blocking binding of elongation factor (arrests protein synth)

Salmonella

• over 2,500 serologic variants
• serogrouping: A- I based on O antigen
• s tyhpi (D1) and paratyphi A are important (typhoid fever)
• animal reservoir: poultry, beef, pork, eggs, lizards, snakes and turtles
• vehicles: food, pets, infected humans
• inoculum: 10⁶-10⁸
• nontyphoidal and typhoidal
• not considered normal flora
• diseases: typhoid (enteric) fever, gastroenteritis, bacteremia (w/ or w/o localized extraintestinal manifistations and asymptomatic
• unlike shigalla, salmonella can get into the blood stream 

Salmonella

Pathogenesis

• invade M cells in pyers patches
• salmonella pathogenicity island 1 (SPI-1)
• type III secretion system-encodes: proteins-insert into cytplams, 
• promote actin polymerization, 
• cellular ruffling and endocytosis
• PhoP/PhoQ regulatory system

Typoid Fever

• s. typhi of salmonella (enterobacteriaceae
• lamnia propria
• uptake by mononuclear cells (regional lymph nodes)
• primary bacteremia: spread to liver, spleen, mesenteric nodes, marrow
• septicemia
• persistent fever, multiple organ involvment (spread to gall bladder may result in carrier state and persistent excretion in stool
• treat blood stream infection 
• found with people that were traveling
• vaccines for typhoid

Yersinia

• enterobacteriaceae
• Y. enterocolitica: animal reservoir, cold enrichment (likes it cold), mesenteric lymphadenitis, gastroenteritis, bacteremia, meningitis
• y. enterocolitica outbreak big in winter times (especially new years day from pork)
• yersinia pestis: bubonic (buboes lymph nodes in groin and axilla), septicemic (buboes w/ bloodstream invasion), pnemonic (septicemic form reaching the lungs 

anaerobic bacteria

• low oxidation-reduction potential is required
• energy by fermentation
• colonization of oxygen deficient microenvironments around the body (mouth and lower GI)
• opportunistic (clostridium most aggressive)

Clinically Common Infections

Anaerobes

• intra-cranial, oral/dental abscess
• skin and soft tissue infections
• aspiration pneumonia
• Pleuro-pulmonary infections
• intra-abdominal infections
• pelvic infections
• bacteremia
• endocarditis

Clinical Presentations

• foul smell/discharge
• location, location, location
• festering of trauma
• necrotic tissue
• abscess formation
• gas in tissue/crepitus

Peptostreptococci

• gram positive anaerobe found in colon
• normal flora of GI, respiratory tract, vagina and skin
• 20-40% of the anaerobic infections: bacteremia, pleuro-pulmonary infections, female genital infections, skin and soft tissue infections

Veillonella

• gram negative anaerobic bacteria
• normal flora of mouth, upper airways, GI tract, and vagina
• predomnantly mixed infectinos (likes friends)
• veillonella parvula: osteomyelitis, meningitis, can cause infection as a solo pathogen
• veillonella dispar and alcalescens: bacteremia nad endocarditis

Non-spore forming

anaerobic bacilli

• actinomyces
• lactobacillus: normal flora for the GI tract and vagina, ferments glucose to lactic acid to make vagina pH less than five
• mobiluncus
• bifidobacterium
• eubacterium
• propionibacterium: normal flora for skin

Bacteroides SPP.

• small coccobacillus, obligate anaerobe, non spore forming
• mouth, upper resp tract, GI tract, urogenital (aprox 30% of stool isolates)
• major conversion of glucose to butyric acid
• mixed endogenous infections 

Bacteroides Fragilis

• pleomorphic rods w/ rounded ends in pairs enclosed in a capsule
• very resilient, aerotolerant
• ferments glucose to lactate, fumarate and malate
• virulence factors: capsular polysaccharides, pilli, neuraminidase, proteases, enterotoxin, hemagglutinin, and adhesis

Fusobacterium SPP.

• fusiform: elongated bacilli w/ swollen center and pointed ends
• gram negative bacilla
• normal flora of the oral cavity, large intestine, and genitourinary tract
• virulence factors: LPS, leukotoxin, hemolysin, phospholipase, proteases, adhesins

Prevotella spp

• gram negative anaerobic bacillus
• extremely small, bile sensitive, saccharolytic bacilli
• normal flora of the mouth, upper resp tract and vagina
• virulence factors: lipopolysaccharides, proteases

anaerobe culture

and identification

• aspirated pus or fluid
• tissue specimen
• require specialized transport media
• pre-reduced blood agar (general growth media)
• thioglycolate broth: generalized borth enrichment media
• bacteroides bile esculin (BBE) agar
• phenylethyl alcohol (PEA) agar
• for identification: gram stain, colony, and biochemical tests (fermentation, detection of metabolic products by gas-lipid chromatography)

Non-pharmacologic intervention

for anaerobic infection

• necrosis=scalpel
• abscess need to be drained
• debridement
• remove obstructions
• hyper-baric oxygen therapy

Antimicrobials and Antitoxins

Anaerobic infections

• beta lactams: penicillins (gram positive only), lactam and lactamase combos, cefoxitin, cefotetan, and carbapenems
• moxifloxacin
• tetracyclins, glycylcycline, metronidazole and nitazoanide (used if anaerobe not major pathogen)
• anittoxins specific for each organisms: clstridium tetani antitoxin and clostridium botulinum anti toxin

What Is an antimicrobial?

• enzyme inhibitor or structure
• disruptor
• bacterial not human targets
• antimicrobial targets unique to bacteria: peptidoglycan, membrane, DNA topoisomerases, ribosome and metabolism
• inhibits essential enzyme
• kills rather than inhibits growth
• broad spectrum w/ limited resistance
• cheap and plentiful

Types of Antibacterials

• bacteriocidal (antilife): slower acting (inhibits an essential enzyme, or important pathway); or 
• faster acting: dirsupts an essential structure (ribosome or membrane
• Bacteriostatic: inhibits gorwth only when present, lets immune system kill bug

Mechanism Antibiotic Resistance

Inhibitors of Peptidoglycan Synthesis

• beta lactams: penicillins, cephalosporins, etc
• vancomycin
• bacitracin 

Beta Lactams

• penicillin, cephalosporins
• four member (unstable) ring that can get cleaved attached to thiazolidine ring
• target: crosslinking of peptidoglycan (PG): backbone of drug looks like DAla DAla
• Penicillin binding proteins (PBP): dAla transpeptidase and carboxypeptidases, importnat for cell growth
• Mechanism of killing: inh of peptidoglycan syn, autolysis due to degradation of PG w/o synthesis
• requires growing cell to work!!
• outer membrane block, poor binding and lactamases and non growing or cell wall lacking cells are resistance to it (mycoplasm)

Beta Lactamase

Derivatives and analogues

• Penicillins: benzyl penicillin (G), ampicillin (also gram negs), and methicillin (beta lactamase resistant)
• cephalosporins
• monobactams, imipenems, carbapenems
• beta lactamase inhibitors: sulbactam, clavulanic acid
• made ampicillin- hydrophillic to get into gram negs (benzyl is hydrophobic) 
• made methicillin bulky so that it is resistant to beta lactamase
• all of them have four member ring 

Methicillin Resistant S. auerus

(MRSA)

• beta lactamase does not work on methicillin
• alternative mechanisms of resistance:
• altered transpeptidase (PBP2A) does not bind penicillin
• PBP2A is both a transglycosylase and transpeptidase
• Chromosomal (natural) and plasmid carried gene
• MRSA plasmid encode additional virulence factors

Vancomycin (Teicoplanin)

• inhibitor of petidoglycan synthesis
• big complex structure
• binds to d ALA -D Ala of peptide (clamps)
• blocks extension and crosslinking
• only for gram positives (MRSA ect)
• resistance (VRSA or VRE): thicker cell wall, use of D ala-d-lactate or other ones instead of d-ala-d-ala

Bacitracin

• peptide antibiotic
• binds bactoprenol-PPi: prevents recycling of bactoprenol (stops conveyor belt) 
• gram positives
• topical ointment w/ neomycina nd polymyxin

Disruptions of membrane structure

• polymxin, colistin, and daptomycin: cationic peptide w/ FA tail (staph or gram negs, topical ointments w/ neomycin/bacitracin
• Bacitracin: peptide, topical ointments, and distinguishes Group A from other strep
• isoniazid ethionamide: antimetabolites, inhibits mycobacterial mycolic acid (wax)

Quinolones

(ciprofloxacin

• inhibition of DNA synthesis (ciprofloxacin/nalidixic acid)
• targets topoisomerase II or topo IV: prevents maintenance of DNA, gyrase from connecting cleaved strands and replication, recombination and repair
• broad spectrum: not anaerobic bacteria, fluoroquinolones used (improv on nalidixic acid
• Resistance: mutation in target enzyme, proins in gram neg outer membrane determine perm, and pumps promote eflux

Inhibitors of RNA synthesis

• rifamycins (rifampin or rifabutin)
• large drug structure
• target is bacterial RNA polymerase: mycobacterium (TB), staphylococci and N. meningitidis
• resistance: mutated polymerase, most gram negs because of poor perm and used in combinations due to rapid development of re sistance

Inhibitors of Protein Synthesis

• inhibits ribosome
• only -cidal one is aminoglycosides
• rest are all static
• tetracycline
• chloramphenicol
• macrolides (erythromycin)
• lincosamides(clindamycin)
• linezolid

Tetracyclines

• bstatic protein synthesis inhibitor
• inhibits binding of tRNA to mRNA/ribosome complex
• binds calcium (chelator)
• actively transported into/out of cell
• gram pos and neg
• resistance: pumped out of cell

Aminoglycosides

• bcidal protein synthesis inhibitor
• prototype is streptomycin: irreversible binding to 30S causing misreading and prevents initiation of translation
• gram neg and positive but toxic side effects
• resistance: change in ribosomal binding site, decreased uptake/perm, modification by plasmid encoded enzyme, anaerobes cannot power the transport of drug

Metabolic Inhibitors: Folic Acid Pathway

• sulfonamides (bstatic): comp inibitor of aminobenzoic acid and external source of end products makes resistance
• trimethoprim: folate analogue that blocks dihydofolate reductase
• dapsone and p aminosalicyclic acid:m tuberculosis
• do not give to pregnant women

Variable heavy and Light domain

• Variabe heavy (Vh) domain is comprised to 3 gene segments: Variable (V), Diversity (D), Junctional (J)
• variable gene codes for 90 AA and the others 10ish
• Variable Light (Vl) domain is comprised of 2 gene segments V and J
• first rearangement is DJ than VDJ for heavy chain
• light chain DNA is next  and VJ of kapp is first than DNA of lambda 
• 2.7 million different variable ends (antigen binding sites)

Minimum bactericidal concentration

• minimal concentration to kill greater than 99.9% of viable bacterial in an 18-24 hr period

Bactericidal Agents

• beta lactams: penicillins, cephalosporins, carbapenims, monobactam
• aminoglycosides
• fluroquinolones
• preferential use: endocarditis, meningitis, ozteomyelitis, and immunocompromised host

Inducible Beta-Lactamases

• Found in SPACE organisms
• Serratia
• Pseudomonas
• Acinetobacter
• Citrobacter
• Enterobacter
• avoid treating w/ beata lactams    if possibe

Time Dependent Killing

• characterized by T>MIC and AUC/MIC
• want conc 2-4X MIC throughout the interval
• concentration doesnt influence faster killing
• minimal to no post antibiotic effect
• goal of therapy: maximize duration of exposure above MIC
• associated w/ cell wall agents: beta lactams and vancomycin

Concentration Dependent Killing

• characterized by Cmax/MIC and AUC/MIC
• want concentration 10X MIC throughout the interval
• associated post antibiotic effect
• goal: maximize concentrations
• drugs: aminoglycosides, daptomycin, fluoroquinolones, metronidazole, amphotericin B and azithromycin

Drugs w/ post antibiotic effect

• time during which bacterial growth is inhibited after antibiotic concentrations have fallen below MIC
• influenced by types of organism, class of antibiotic, conc of antibiotic and duration of exposure
• aminoglycosides, fuoroquinolones, tetracyclines and clindamycin
• typically a once a day or every other day very large dose

Complement Overview

• key role in defense against bacteria, fungi and some parasites
• most important functions are:
• opsonization
• mediators of inflammation (a fragments): attraction and opens vasculature (anaphylaxis)
• direct killing of organisms
• facilitates antigen-activation of B cell

Pathways of Complement Activation

• Alternate (innate): microbial and other surfaces (unless inactivated); LPS's
• Lectin (innate): mannose-binding lectin (MBL) that binds to pathogen surface
• Classical (humoral): Ag-Ab complexes or C-reactive protein

Complement Consequences

• three pathways of proteases which coalesce at C3
• cleavage products have activity
• produce chemotaxins: C5a
• produce anaphylataxins: C3a, C4a, C5a: induce small muscle contr, vascular permeability, 
• C3a and C5a induce sticky molecules (act of integrins)
• C3a and C5a activate mast cells to release histamine and TNFa
• opsonizes microbe: C3b
• activates B cell: C3d
• produce membrane attack complex: C5-9: especially gram neg bacteria and niesseria

Classical Pathway

• antigen-antibody complexes are main activators of this pathway (change in Fc conformation enables C binding): soluble Ag-Ab complexes (IgM or IgG) or Ag-Ab on a target cell (same Ig)
• C1q binds to the CH3 domain of IgM or CH2 domain of IgG and both require at least two adjacent Fc regions
• IgM is more effective at activating complement than IgG
• C-reactive protein binds to the surface of many bacteria and is also an activator
• cleavage of thiol ester bond of C4 causes covalent attachment to antigen
• C4b and C2a combnine to form C3 convertase

Lectin Pathway

• antibody independent pathway" components are dsignated by abbreviations and numbers (MASP-1 resembles C1)
• mannose-binding lectin binds to mannose and similar sugar residues on foregin surface
• binding activates MASP-1 and MASP-2 that cleave and activate C4 and C2
• cleavage of thiol-ester bond in C4 causes covalent attachment to antigen
• cleaved C4b and C2a generate C3 convertase
• converges w/ the classical pathway at activation of C3

Alternatve Pathway

• Antibody independent: designated by letters
• initiated by spontaneous C3 cleavage and sticking to cell surface proteins
• produces active C3 and C5 convertase
• host cell's membrane proteins inactivate C3 and Stop progression
• DAF, MCP, H, and I prevent spontaneous attachment of C3a

Activities of C3 Fragments

• C3a promotes inflammation
• C3b fixation to surfaces leads to opsonization
• C3b fixation leads to immune complex clearance: C3b biunds to complement receptor 1 ( CR1) on phagocytic cells
• C3b bound membrane anchors C5 convertase activity and later steps of cascade'
• C3d bindsd to antigen and CR2 (C3d receptor/EBV receptor) to facilitate actiavtion

C5 Convertases

and

on

• C4b2b3b forms C5 convertase
• alternative pathway: C3bBbC3b forms C5 convertase
• cleaves C5 to C5a and C5b
• C5a relased into fluid phase: potent anaphylatoxin, potent chemoattractant and INFLAMMATION
• C5b binds to the cell surface: anchor for binding the terminal complement components
• C5b, C6-9 are terminal and common to all pathways
• terminal components form MAC and result in cell lysis

Complement-Mediated Cytolysis

• only works if complement can build upon a membrane (MAC)
• works especialy well on Neisseria, easy to get to plasma membrane
• Gram positive bacteria resistant because of Cell wall
• works well on gram negs though
• lysozyme can cleave peptidoglycan so complement can get close to gram positive cell walls

Regulation of Complement Activity

• A suicide substrate mechanism, in which an inhibitor forms a covalent bond with the active site of the enzyme (C1 inhibitor binds to C1r and C1s and prevents it from becoming proteolytically active)
• proteolytic digestion of the active fragments into smaller inactive fragments
• inhibition of association of complement components

Factor 1 

Regulation of Complement Activity

• proteolytic digestion of the active fragments into smaller inactive fragments
• digestion of C4b and C3b 
• MCP acts as cofactor for factor 1 mediated proteoltyic cleavage of C3b
• especially in alternate pathway where DAF displaces Bb from C3bBb

Complement Deficiency and

Clinical Syndromes

• C1q, C1r, C1s C4 or C2: results in suboptimal C3b and increased risk of pyogenic bacteria (lupis like immune complex disease)
• C3:  results in no C3b and recurrent infections w/ pyogenic bacteria and NEisseria (immune complex disease)
• C5, C6, C7 or C8: results in no MAC and Neisseria infections and no immune complex disease

Normal Flora Glossary of Terms

• pathobiont: refers to a member of the microbiota that under specific conditions can cause pathology
• dysbiosis: state of microbial imbalance, may produce a disruption in the homeostasis btw host and the microbial community
• prebiotic: food ingrediate that supports the growth of beneficial properties of one or more resident gut symbionts
• probiotic: a live microbe that when ingested provides benefit to the host either directly through interactions w/ host cells or indirectly through effects on members of the microbiota

NOD-like Receptors (NLRs) and

microbiota

• recognize microbial molecules w/i cytopasm
• deficiency of a specific NOD reduced IL-18 levels which may alter the microbiota and lead to colitis

Acute Inflammation

Characteristic Tissue Changes

• expansion of capillary bed: hyperemia, due to change in permeability and slowing of flow
• increase i interstitial tissue: edema, d ue to an increase in vascular permeability and escape of protein containing fluid into the interstitium
• migration of inflammatory cells into the tissue: involves mediator modification of endothelium resulting in attachment and transmigration of neutrophils and macrophages into the tissue

Integrins and 

Inflammatory response

• interaction of mediators w/ slowed rolling induces activation of integrins, most notably LFA-1 or CD11/18, on neutrophil surface
• these integrins interact w/ endothelial surface ICAM-1 to hold neutrophils tightly in place so that migration of neutrophils into tissue can occur
• this tight binding is also called margination
• once bound, integrins expressed on surface interact w/ molecules at the junctions btw endothelial cells, most notably PECAM-1 or CD31
• neutrophils elongate and pass btw the cells, a process called diapedesis or transmigration 

Acute Phase Proteins

(inflammation)

• role in promotion of or protection during acute inflammatory rx
• pentraxins: increase markedly (100fold) in concetration ripdly, non-specific bacterial opsonins, and C-reactive protein (CRP) and amyloid protein
• complement proteins: 10 fold increases
• Proteinase inhibitors: alpha-1 antitrypsin and alpha 1 antichymotrypsin
• metal binding proteins: espicially iron, copper and zinc (removes from serum so bacteria cant use it)
• negative reactants: stops synthesizing albumin and transferrin

Acute inflamation in Meningitis

• organisms are present in cerebral spinal fluid (CSF) and that is where the acute inflammatory reaction occurs
• changes in chemical constituents reflect the changes in vascular permeability
• cells move into the CSF which normally does not contain significant numbers of cells
• because one is dealing with an enclosed fluid space the number of ogranisms can become quite large

Active Acute Inflammation

Termination Mechanisms

• witch from proinflammatory leukotrienes to anti inflammatory lipoxins
• cytokine scavengering by non-functional or soluble receptors
• release of anti-inlflammatory cytokines, including transforming growth factor beta (TGF) and IL-10 from macrophages
• production of antiinflammtory lipid mediators, called resolvins and protectins, derived from polyunsaturated fatty acid
• there are circulating cytokine antagonists that help to limit the extent and severity of the acute phase reaction

Community Acquired Staphylococcus

Protein A and Fc Cloaking

• virulent staphylococcus ahs a gene spa which produces protein A which is excreted 
•  protein A has high affinity for human IgG fc region and acts to cloak bacteria and prevent binding to phagocytes
• staph infecting hcikens lack this protein but chick Ig Fc differers greatly
• genetically engineered protein A is useful in human immunoglobulin capture and purification

Community Acquired Staphylococcus

Panton-Valentine Leukocidin

• Panton=Valentine leukocidin (PVL) is a polymer consisting of two peptides secreted by staph which can bind to and lyse white cells
• CA- MRSA which causes necrotizing pneumonia in otherwise healthy individuals is always associated with PVL production
• PVL may be why CA-MRSA is so virulent (evidence exists to both support and refute)

Sweet Syndrome

• sweet syndrome (acute febrile dematosis) w/ extensive necrotizing extracutaneous involvement (soft tissue, skeletal muscle, uterus anad placenta)
• sweet syndrome consists of abrupt onset of erythematous skin lesions on biopsy shows dense dermal neutrophil infiltrate, there is fever and neutrophilia. cultures are negative. responds to steroids
• underlying mechanism is incompletely understood-thought to be dysregulation of cytokinese especially GM-CSF. Levels are consistently very high in patients. sweet syndrome has been associated with neoplasms which secrete GM-CSF and occurs in marrow donors stimulated with GM-CSF
• studies of nucleotide polymorphisms suggest an underlying genetic predisposition related to a locus on chromosome 3

Inflammation Initiators

• tissue damage: release of interleukin 1, uncovering of alternative complement activation structures, release of proteases, phospholipases and other proteins and release of DAMPs(damage associated molecular pattern molecules
• infection
• immune responses (hypersensitivity): example poison ivy

M Cell

• internalizes antigens for priming immune response
• found in colon
• grabs stuff and brings it to a peyers patch

Recruited T Cells

• Th17 Cells: activated by DC (IL1 and TGFβ) or IL23; reinforce peithelial cella nd neutrophil function w/ cytokines
• Th1 cells: activated by DC and IL12p70; reinforce macrophage, DC, LC inflammatory responses, promote antibody class switch
• Treg Ce lls: always active, regulate other responses and produce TGF beta and IL10
• helper t cells and said dont need to know well

Variable Heavy (Vh)

Gene segments

• 3 gene segments
• V: variable gene segments code for about 90 amino acids
• D: diversity gene segments code for 10 amino acids
• J: junctional gene segments code for 15 amino acids
• 38 V gene segments, 27 D segments and 6 J segments

Recombination Active Genes

• Rag 1 and Rag 2 enzymes
• active only in cells that undergo rearangement of their DNA (developing B and T cells)
• both bind recognition signal sequences
• orientate the DNA allowing the V and J coding sequences to align
• unwanted DNA is looped out and excised
• coding sequences connect (junctional diversity)
• if you dont have Rag you cannot make B cells and T cells causing SCID or Omenn Syndrome

Mechanism of Junctional Diversity

• Rag allows for unwanted DNA to be excised leaving two blunt ends on exons
• phosphodiesterase hair pin bond forms between the two
• Rag genes will nip DNA to create a 3' overhang
• enzymes come in and new nucleotides are added that arent coded for by germline
• called the P region (palindrome)
• terminal deoxynucletidyl transferase addes these nucleotides that werent coded for (up to 20) (N region diversity)
• Ligase will connect everything
• w/ junctional diversity the total diversity for variable end of the antibody aproaches 10¹¹ 

Somatic Hypermutation

• following Ag Contact
• primary response it makes IgM
• B cells go into follicles of lymph node to germ center
• undergoes somatic mutation at or near variable end (meant to help you increase affinity)
• makes a bunch of mutations and the one with the highest would bind to the limited antigen brought there
• occurs in secondary follicles
• requires follicular T helper cells in the form of CD40 ligand

Vibrio

General

• short, curved, gram neg rods that are highly motile
• grow in alkaline conditions (selective media)
• oxidase positive
• V. cholerae, V pharahaemolyticus, V. vulnificus
• V. cholerae has O1 serogroup (and O139) and non O1 serogroups
• O1 serogroups have serotypes ogawa, inaba and hikojima and biotypes classical and El Tor

Vibrio Clinical manifistations

• V. cholerae serogroup O1: epidemic, pandemic cholera
• V. cholerae serogroup O139: cholera and milder diarrhea
• V. parahaemolyticus: gastroenteritis (seafood)
• V. vulnificus: wound infection

Vibrio

Virulence and treatment

• orally ingested
• gastric acid inactivates the organism (requires high inoculum)
• colonizes small intestine
• requires attachment ot cause diarrhea: toxin coregulated pilus (tcp A)
• elaborates enterotoxin - cholera toxin 
• treated with IV fluids, monitoring of output, oral rehydration and tetracyclin (TMP/SMX)

Vibrio

Cholera Toxin

• 1 a subunit, 5 b subunits
• A subunit 2 components: A1 is catalytically active and A2 binds to B
• B subunit binds to GM1 ganglioside
• activation of adenyl cyclase
• causes water to pour out into the lumen
• same as LT toxin of ETEC

non-cholera

Vibrio Infections

• Vibrio parahaemolyticus: gastroenteritis, shellfish associated
• virbio vulnificus: wound infections, severe cellulitis, water associated injuries and shellfish associated

Campylobacter

• gram negative comma shaped rods
• 5-10% O2, 10% CO2 (grows best in campy jar)
• selective media: campy- BAP
• campylobacter jejuni grows best at 42 degrees C
• survives at 4C for up to several days
• C. jejuni, coli, fetus, laridis and others
• Campylobacter reservoirs: cattle, swine, goats, sheep, poultry, pets (young), food and water
• transmitted by fecal-oral transmission
• usually surface bacteria on food 

Campylobacter

Clinical Manifistations and

post infections complications

• C. Jejuni: gastroenteritis: secretory or inflamm diarrhea, pseudoappendicitis and bacteremia (rare)
• C. Fetus-septicemia: opportunistic infection, meningitis and other organ systems
• post infection compl: arthritis, reiter syndrome, seizures (conjunctivitis), seizures, guillain barre syndrome (antibodies mimic host ganglioside structure and cause rising paralysis)

Campylobacter

pathogensis

• following for c. jejuni
• Lipooligosaccharide (immune avoidance, molecular mimicry)
• surface adhesins
• flagella: chemotaxis (AA of chick GI tract and components of mucus)
• toxin production: cytolethal distending toxin (arrest of cell cycle)
• C. fetus uses surface (s) protein: disrupts C3b binding, renders resistant to  phagocytosis and sustains bacteremia

Heliocobacter pylori

• microaerophilic curved gram negative rods
• multiple flagella
• produces large amounts of urease
• grows optimally at pH 6-7
• utilizes the mucus layer overlying mucosa (and adheres to mucosa)
• inhibits local acid production
• neutralizes pH with urease production (urea into NH4 and CO2)

H. pylori

Virulence factors

• induce inflammatory responses: various virulence factors involved
• CagA protein: CagA strains more virulent (inducer of IL-8); encoded by cag pathogen. idland and type IV secretory system that is highly complex
• vacuolating cytotoxin: secreted vacA gene product induces pore formation in the cell membrame, vaculation in tissue cultures and promotes apoptosis (peptidic ulcer disease)
• BabA/B - blood group antigen binding: adhesin enhances binding to gastric mucosa

Helicobacter pylori

clinical features

• acute infection: may persist 1 year (nausea, vomiting, abdominal pain)
• chronic infection: years lifelong: chronic superficial gastritis, gastric and duodenal ulcers, chronic arophic gastritis (gastric adenocarcinoma and lymphoproliferative disease)

H. pylori diagnosis and treatment

• invasive (endoscopy): culture (5% O2), PCR, and histology
• noninvasive: serology (ELISA), urea breath test and stool antigen detection
• relapse is common (in vitro not in vivo effectiveness)
• acquired resistance is a concern
• single antimicrobial regimens not effective
• standard aproaches: triple therapy (typically 2 antibiotics w/ acid supressing regimens
• quadruple therapy (2 antibiotics, PPI and bismuth salt therapy
• sequential therapy (PPI, antibiotic, PPI than two antibiotics

Cytokine Storm Inducers

• pathogen associated molecular patterns: cell wall components and double stranded RNA or DNA (virus)
• toxic Shock syndrome toxins (superantigens)
• sytemic viral infections (later in course)

Gram-negative vs. gram-postive inducers

• gram positives: cell wall structure: TLR2, inflammasome etc; and superantigen exotoxins
• Gram negative: LPS that sets off TLR 4 and is highly immunoreactive 

Toll Like Receptors (TLRs)

• innate immunity recognizes uniqure repetitiveness of microbial structures (PAMPs)
• ligand binding triggers intracellular transduction
• Ten TLRs identified in humans
• recognize similar structures - lipids nucleic acids
• interact direct interaction or via intermediate PAMP binding molecule
• ability tor ecognize structurally and biochemically unrelated ligands (LPS by TLR4)

Primary mediators of storm

• cytokines that activate macrophages: innate TNF alpha, IL1 and interferons alpha and beta
• immune cytokines: IL17 and IFNgamma

Responses to TNF-alpha

• induces production of IL-1, IL6 and acute phase proteins
• facilitates diapedesis of neutrophils
• loss of muscle, body fat, and appetite (cachexia)
• neutrophil activation
• kills cells
• NO production from macrophage
• decreased vascular tone and cardiac output
• FEVER

Sepsis

• clinical condition resulting from complex interactions btw pathogens and host immunity which results in systemic inflammatory and ocagulation responses
• sepsis and spetic shock highly complex
• Death secondary to a vigorous and exaggerated immune resposne due to: cytokines, chemokines, prostaglandins, lipid mediators and ROS
• vasodilation, upregulation of adhesion molecules, activation of WBCs and endothelial cells, myocardial suprression and coagulation system activation

s. pneumoniae

Sepsis

• cell wall, polysaccharide capsules, exotoxins all responsible for inflammatory response
• activate the alternative pathway of complement cascade
• bind the acute phase reactant C reactive protein
• activate procoagulant activity on the surface of endothelial cells
• induce production of cytokines, NO and platelet activating factor (PAF) upon binding to eptihelial and endothelial cells
• initiate the influx of neutrophils

Staphylococcus Toxic Shock

• fever: temp > 102
• rash
• desquamation
• hypotension
• multi-system involvement
• negative results: 
• blood, throat, CSF (blood could be positive)
• rise in RMSF, leptospirosis or measles titer

Superantigen

• bacterial exotoxins cross-link MHC class II molecules on APC outside peptide groove to TCR on T cell
• each superantigen is known to interact with a family of V (beta) elements of T cell receptor
• uncontrolled release of pro-inflamm cytokines (TNF-a, IL-1, IFNy)
• clinical sequelae: SIRS, Shock (toxic shock)
• paradoxical effects: powerful proliferative effect on t cells, but also produce a profound state of Tcell unresponsiveness and even death
• production of pores on cell membranes: endothelial contracile microfilaments and influx of ions and small molcs
• inhibit myocardial and pulmonary function: elevated pulm artery pressure, pulm edema and elveated ventilation pressure

Hemophilus influenzae

• colonize human respiratory tract
• encapsulated (serotypes a-f, most important Hib): conjugated capsular polysaccharide vaccine
• mucosal disease-pneumonia, brochitis, otitis and occasionally invasive disease
• small gram neg pleomorphic rod, facultative anaerobe and non motile
• fastidious, oxidase +, factor X and V
• capsule and outer membrane does adherence
• LPS elicits strong immunologic and inflamm resposne

Sepsis Therapeutics

• sepsis induces procoagulant state
• inflammatory cytokinesactivate the coagulation cascade and inhibit fibrinolysis-disseminated intravascular coagulation
• Treatments: activated protein C-potent anticoagulant and profibrinolytic enzyme
• inhibitors of SIRS, NO induced vascular dysfunction, apoptosis of lymphocytes and PMNs activation
• drotrecognin alfa (activated) 

Immunoreceptor Tyrosine-based Activation Motifs

(ITAM)

• Igα and Igβ transmit signals via this
• they are bumped by the Fc region of the heavy chain after activation whic causes them to transmit signal
• C3d on antigen can bring together CR@ molecule to also signal through CR2:CD19:CD81 as well as ITAM 
• no T cells are involved here

Clonal Selection 

• each B cell advertises its product on the membrane
• the B cells with the best Ig binds the antigen and gets stimulated
• as more cells make higher affinity IgM: strength of antibody increases
• the immune response matures

T-Cell Independent Antigens

• antigen and B cell activator: LPS
• antigen and receptor cross linking activation: bacterial polysach, polymerized flagellin, membrane glycolipids and Nucleic Acids
• facilitated by C3d
• facilitaed by TLR stimulation
• may require cytokines from acute phase or other capsules
• bacterial polysaccharides found in capsule or biofilm (Making IgM essential to elliminate these)

B Cell Class Switch

• requires T cell help
• B Cell-T cell interaction: T cell receptor inteaction w. B cell (CD40=CD40L
• cytokine determines type of antibody
• recombination of VDJ w/ new heavy chain gene regeion deletion out invervening sequence
• does not change the antigen binding regions (VDJ)
• want same specificity w/ a different functionality
• depending on whats deleted you can get: IgD and IgM becoming IgG, IgE or IgA (from chainging heavy chain genes) 
• binding of CD40 to B cell is by peptide so they only developed against a protein antigen

Afiinity maturation due to somatic hypermutation

• T cell help (CD40L-CD40) induces production of a mutation promoting enzyme
• T cell help promes B cell growth
• VDJ in Ig gene undergoes mutations (1/1000 bps)
• clonal selection (best BCR gets to grow!)
• T cell resue of best IgG producing B cells

Development of Antibody Response in Serum

• T independent antibody: IgM
• clonal selection enhances antibody strength
• T cells provide help to b cells: cytokines determine class switch and type of antibody
• Affinity maturation and clonal selection: somatic mutation of VDJ portion regardless of heavy chain in growing B cells
• lower affinity IgM producing cells cant compete with IgG, IgE or IgA producing B cells for clonal selection and dissapear: except for polysaccharide antigens!!!
• B cells differentiate into memory B cells and plasma cells

Primary Antibody Responses

• inducible by both T ind and T Dep Ag
• Starting from naive B and T cells (no memory cells)
• longer lag period (4-7d)
• gradual rise in Ab titer
• initally all IgM, later (6-8 days) class switching for IgG, IgE and IgA
• lower Ab affinity (limited affinity maturation)

Secondary Antibody Responses

• inducible by T dependent Ag only
• memory B and T expansion
• shorter lag period (1-3 days)
• rapid rise in Ab titer
• mostly IgG, IgA or IgE (due to class switching)
• a more persistent response
• higher Ab affinity with time (affinity maturation)

Primary B Cell Abnormaliites

(3 yo w/ history of bacterial infections)

• X linked agammaglobulinemia: defect in brutons tyrosine kinase, no naive b cells nor IgM
• X linked hyper-IgM syndrome: defect in CD40L in T cell and b cell can not mature (class switchm no memory); little IgG and high IgM
• common variable hypogammaglobulinemia: herogenous group, low amount of IgG and IgA

Structure of MHC I and II    

• structure: immunoglobulin-like strc; two different subunits
• MHC I (HLA A, B, C): heavy chian and beta 2 microglobulin, cloded ended peptide binding pocket and forms trimers
• MHC II (HLA DP, DQ, DR): Alpha and beta chains of similar size, open ended peptide binding pocket
• peptides that bind to MHC II and be larger and floppier (not as defined in size)
• get the sets from both mom and dad
• additional binding sites inside pocket that make them more specific for specific peptides (pathogens)Can only bind a peptide!!!!!
• size of binding peptide: MHC 1 (8-9 AA) and MHC II (11-12+)

Properties of MHC

• co dominant expression (sets from both mom and dad) increases number of different MHC molc that can present peptides
• polymorphic genes: many different alleles in population ensure that diff individiuals can respond to diff microbial peptides
• Class II proffesional APCs, macrophages and bcells (cd4 helper t cells interact w/ dendritic cells, macrophages and b cells)
• Class 1 (all nucleated cells): CD8 CTL can kill any virus infected cell
• each MHC displays only one peptide at one time
• low affinity but broad specificity (many dif peptides can bind to one MHC molc
• verly slow off rate (displays for long time)

MHC I Properties

• on all nucleated cells
• binds to CD8 molcs on TCells
• binds a single linear peptide of 8-9 amino acids
• peptide reflects intracellular antigens

MHC II Properties

• on antigen presenting cells: macrophages, DC, B cells
• binds to CD4 molecules on T cells
• binds a single linear peptide of 11-13+ amino acids
• peptides from exogenous material (debris)

CD1 (a-e)

• MHC I like structure: heavy chain and beta 2 microglobulin that binds glycolipids
• gene on chromosome 1 (not MHC locus)
• recognized by NKT and other t cells
• important for innate response  (especially against tuberculosis)

 MHC Locus

• major MHC locus: chromosome 6
• genetic locus containing immune response genes: MHC I (HLA, A, B, C) and MHC II (DP, DQ, DR)
• MHC molec are highly polymorphic (diff alleles in population)
• co-dominant expression (3 from each parent)
• other genes w/i MHC locus (associated w/ immune responses
• disease associates (increased risk 4-100 fold): immune response mediated and epitope presenting?

MHC II Antigen Presentation

• MHC II acquires antigenic peptides from lysosome degraded material -- Exogenous trash (debris)
• exogenous trash is only presented by antigen presenting cells (APC)
• APCs: dendritic cells, macrophages, B cells and others on special occasions

MHC II Synthesis and Antigen Acquisition

• proteins phagocytosed and endosome acts w/ lysosome
• In ER MHC II molecules are being made and invariant chian binds to cleft of MHC II molc and blocks things from going in
• complex moves from ER to golgi to Lysosome
• Invarient chain gets clipped producing the CLIP protein in the lysosome 
• HLA-DM helps put peptide into cleft and sends MHC II to cell surface
• now a CD4 T cell can read the peptide

MHC I Presentation of Antigen

• in all cells: MHC I acquires antigenic peptides from endogenous proteins which get transported into the ER
• In some APC: MHC I acquires some exogenous trash delivered to the ER for cross presentation (dendritic cells are the best at cross presentation)
• potentially any protein with in a cell
• proteins identified for degradation, misfolded, viral proteins in cell, tumor antigens, MHC molecules (transplants) and signal peptides

Which Peptides will become T Cell Antigens

• proteins in higher concentration in cell
• ptoential for ubiquitination
• potential for degradation by proteosome and traversal of TAP channel (into ER)
• able to bind to MHC I molecules

Cross Presentation

• phagocytosed proteins
• exogenous material is sent to the ER
• peptides are presented on MHC I
• allows activation of CD8 T cells by viral and tumor antigens
• occurs pirmarily in dendritic cells
• differers from endogenous because molecule leakes out of endosome or lysosome rather than just being in cell initially 

Dendritic Cells

• T cell interacting: myeloid, langerhans and plasmacytoid
• B cell interacting is follicular: antigen skticky not APC
• only matures when triggered by a danger signal
• mature DC have a lot longer half life
• regulate IL12, IL23, IL6, IL10, IL18

Myeloid (Interstitial) Dendritic Cells

• location: tissue
• precursors: monocytes or pre-DCs
• Cell surface markers: MHC II, CD4, CD11b, CD11c, CD13 and CD33
• receptors for microbial and cellular debris: iDC: TLRs, CD14 (LPS receptor), lectins, Fc receptors, complement receptors and apoptotic cells
• cytokine production DC1: IL23, IL12, IL6
• DC2: IL6 and other cytokines

Langerhans DCs

• Langerhans DCs: myeloid-like DCs located in the epidermal layer of skin
• contain Birbeck granules
• mature langerhans cells also express MHC II, CD4, CD11b, CD 11c, CD13 and CD33

Plasmacytoid DCs

• found in blood, spleen and lymph nodes
• precursors: pre-DCs
• MHC II and CD4 (CD123, and BDCA-2(blood dendritic cell antigen: C type lectin for sialic acid))
• purpose: cytokine production and antigen presentation
• cytokines: immature plasmacytoid DCs produce large amounts of interferon alpha in response to viruses, espeically envoloped viruses (Herpes simplex virus)
• also produce beta, IL-12 and inflammatory cytokines
• migrate to virus infection site

Follicular DCs

• follicular DCs are sticky cells present in the follicles of the lymph node and spleen and get coated with antigen for display to B cells rather than T cells (like a bulletin board)
• follicular DCs do not process antigen
• folliclular Dcs are important fro B cell stimulation and antibody production

Antibody Effector Deficiencies

• gets severe case of giardia diarrhea and is prone to respiratory infections: IgA deficiency
• IgM present but no IgG, IgE or IgA: hyper IgM syndrome due to lack of T cell helper signaling
• 3yr old prone to bacterial infectinos, esp staph and encapsidated bacteria: complement C3 def
• NK cells cannot kill antibody coated cells: NK cells w/ leukocyte adhesion def weakly bind but not kill antibody coated cells

Overview of Antibody Functions

• neutralization: blocking attachment to cellular receptors, hence function
• Fc mediated activities: complement, opsonization for phagocytes, NK cells,and Fc receptor mediated activites
• Immune Complexes: type III hypersensitivity (C')

Active Antibody Transport

• mucosal secretion of IgA (pIgR mediated): secretory component (cleaved J chian) mediated (one way transeptihelial)
• Bidirectional transport of IgG, IgE (FcRn mediated): across polarized epithelial cells and inflammatory cytokines promote FcRn expression (IgG transport)
• IgE goes from mildly acidic to neutral environment in GI tract  and is important during worm infection

Secretory IgA

• protection of respiratory and GI Mucosa: as first line of defense, can perform many IgG-like functions and regulates local flora
• bactericidal activity: against gram neg organisms in presence of lysozyme
• antiviral, antifungal, antiparasitic: neutralization of attachment
• passive immunotherapy: breast milk
• Synthesized by plasma cells as IgA dimer w/ J chain and is cleaved upon transepidermal passage to produce s component and cleavage of Fc binding site ensures one way transfer
• sIgA producing Bcells migrate to mucosa ass tissues
• Function: agglutination of bacteria and viruses and neutralization of toxins and adherence factors

IgG

• highest conc in blood/longest half life
• transported to EC spaces to protect tissues from infections
• transplacental and endothelial cell transport: mammalian babies have IgG antibody protectino while suckling and can make IgM
• neutralizes toxins and blocks binding of viruses and bacteria
• clumping of particulate antigens and helps precipitation of multi-epitope antigens (agglutination and aggregation)
• activation of complement via CH2 domain
• opsinization: Fc rec and activation of C'
• Antibody dep cell mediated cytotoxicity (ADCC): Fc receptor on NK cells (also eosinophils, neutrophils and macrophages)

IgM

• first ig produced following immunization: primary response, T cell independent and produced against carbohydrates (capsule)
• only calls of Ig syn by fetus and neonate (begins at 5 months gestation)
• primarily a serum atnibody (too big to leave bloodstream)
• most efficient I g for mediating complement fixation (CH3 Domain)
• highest avidity: most efficient agglutinating antibody
• blood group: naturally present antibody reactive w/ A/B blood groups

IgE

• meiates type I hypersensitivity reactions: mast cells and basophils have receptors for IgE Fc portion
• most serum IgE is cell associated
• Ag crosslinking IgE on surface induces degranulation, secreiton of histamine, heparin and other pharmacological agents from granules
• important in parasitic infections

Antibody Induced Pathology

• Allergy (Type 1 Hypersensitivity): IgE mediated
• Autoantibodies (Type 2 Hypersensitivity): complement mediated inflammation
• Immune Complexes (type 3 Hypersens): occurs when antibody-antigen complexes are not adequately cleared (macrophages have difficulty clearing small complexes)
• all lead to inflammation and tissue damage