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Immuno questions, Block 5, set 3
only from the lecture 15 prestudy guide, UTCOM class of 2014
159
Immunology
Professional
03/19/2011

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Term
What is hypersenstiivity?
Definition
state of heightened reactivity to antigen
Term
What is a hypersensitivity reaction?
Definition
immune responses to innocuous antigens that lead to symptomatic reactions upon REEXPOSURE
Term
What is important about hypersenstivity/"allergic" reactions?
Definition
they are dependent upon REEXPOSURE
Term
What type of immune reactant is involved in Type I hypersensitivity reactions?
Definition
IgE
Term
What type of antigen is involved in Type I hypersensitivity?
Definition
soluble antigen
Term
what is the effector mechanism of IgE type I hypersenstivity?
Definition
mast cell activation
Term
What are some examples of hypersensitivity reactions?
Definition
allergic rhinitis, (allergic) asthma, systemic anaphylaxis
Term
What is hypersenstiviity disease?
Definition
damage to host tissues caused by hypersenstiviity reactions to typically innocuous antigens
Term
How did Coombs and Gel classify hypersenstiivty reactions?
Definition
Type I, II, II, IV based on types of antigens that are recognized and the types of immune responses that are involves
Term
What else might people call a Type I hypersenstivity reaction?
Definition
"allergy"
Term
What does Type II hypersenstiivty involve (which immune reactant)?
Definition
IgG
Term
What are the two types of antigens involved in Type II?
Definition
cell or matrix associated antigen/cell surface receptor
Term
What is the effector mechanism involved in Type II and with what antigens are they involved?
Definition
Complement, FcR+ cells (phagocytes, NK cells) with cell/matrix associated antigen; antibody alters signaling in cell-surface receptors
Term
What are examples of hypersensitivity reactions?
Definition
some drug allergies (eg penicillin- complement effector mechanism); chronic urticaria (hives)- antibody against FCepsilonRIalpha receptor
Term
What is a type III hypersenstivity?
Definition
involves production of antigen-antibody complexes
Term
Which immune reactant is associated with Type III and what type of antigen?
Definition
IgG and soluble antigens
Term
What is effector mechanism of Type III?
Definition
copmlement phagocytes
Term
What are some examples of Type III?
Definition
serum sickness, arthrus reaction
Term
What is Type IV hypersensitivity?
Definition
T cell mediated hypersenstivity
Term
Which immune reactants are involved in Type IV?
Definition
Th1, Th2, CTL
Term
What type of antigens are associated with Type IV?
Definition
soluble antigens (Th1 and Th2); cell associated antigen (CTL)
Term
What are the effector mechanisms of Type IV?
Definition
Th1: macrophage activation; Th2: IgE production, eosinophil activation, mastocytosis; CTL: cytotoxicity
Term
What are examples of Type IV reactions?
Definition
Th1: contact dermatitis, tuberculin; Th2: chronic asthma, chronic allergic rhinitis; CTL: graft rejection
Term
What are antigens that selectively stimulate Th2 cells to drive an IgE response and why Th2?
Definition
those antigens are also known as allergens; they stimulate Th2 cells because those CD4s can induce class switching from IgM to IgE
Term
Describe some properties of allergens.
Definition
small proteins; highly soluble; carried on desiccated particles like pollen or mite feces; usually presented at very low doses
Term
What happens once allergens come into contact with the mucosa of the airways?
Definition
the soluble antigens elute from the delivery particles and iffuse into the mucosa
Term
What happens with antigens presented to Th0 cells at low doses?
Definition
elicit differentiation into Th2 CD$ cells
Term
What is the maximum exposure to the common pollen allergens of ragweed?
Definition
less than 1 microgram/year/person- even so, many people suffer irritating and even life threatening to TH2 driven IgE responses to these antigens
Term
Do all people exposed to a particular allergen have an allergic reaction?
Definition
no
Term
Do all allergens have enzymatic activity?
Definition
no, not all, but many common allergens have enzymatic activity
Term
Why might the enzymatic activity of allergens be important?
Definition
IgE is a very important isotype of antibody in the immune response to parasites and many parasites produce and secrete proteolytic enzymes that break down connective tissues to allow worms access to host tissues
Term
What is special about proteases?
Definition
believed to be particularly strong inducers of Th2 type responses
Term
How do Th2 cells stimulate class switching to IgE?
Definition
by delivering several molecular signals that favor class switching in B lymphocytes to IgE
Term
Describe the signaling process of Th2 stimulating class switching to IgE.
Definition
when the TCR of a Th2 cells becomes ligated, the Th2 cell produces and secretes IL-4, IL-5, and IL-13, upregulating surface expression of CD40L and CD23
Term
What do CD40L and CD23 do?
Definition
costimulatory molecules bind counter receptors (CD40 and CD2) on presenting B cell to induce class switching to IgE
Term
What is CD23?
Definition
low affinity receptor for IgE
Term
What are Type I reactions initiated by?
Definition
mast cells (eosinophils and basophils also involved
Term
What do mast cells, eosinophils, and basophils express that is important for Type I reactions?
Definition
they express the high affinity IgE receptor (FcEpsilonRI)
Term
What happens when IgE binds to mast cells/eosinophils/basophils?
Definition
crosslinked by specific antigen, degranulate, releasing a variety of inflammatory mediators that initiate inflammatory responses
Term
What are basophil mediators simmilar to?
Definition
the immunological mediators produced by eosinophils
Term
How are type I hypersenstivity reactions initated?
Definition
degranulation of mast cells; mediators initate inflammation and recruit eosinophils and basophils to the site of inflammation; eosinophils and basophils contribute to inflammatory response by releasing the contents of their granules
Term
Is there a genetic component to allergy?
Definition
yes, there is a genetic basis to allergic predisposition
Term
How do you describe the condition of being predisposed to allergies?
Definition
atopy
Term
Who is more likely to produce IgE responses to common environmental allergens?
Definition
40% of Caucasian population of North America and Europe
Term
How do atopic individuals differ from non-atopic individuals?
Definition
higher levels of soluble IgE and more circulating eosinophils than non-atopic individuals
Term
Which chromosomes are involved in allergic predisposition?
Definition
chromosome 11 encodes a gene for beta subunit of high affinity IgE receptor; chromosome 5 encodes a cluster of genes encoding IL-3,4,5,9,13 and GM-CSF
Term
What are the proteins encodd by chromosome 5 involved in?
Definition
isotype switching, eosinophil survival and mast cell proliferation
Term
What is correlated with elevated IL-4 levels in atopic individuals?
Definition
inherited sequence in the promoter region of the IL-4 gene
Term
Wha else might affect IgE response to certain allergens (HLA)?
Definition
HLA class II polymorphism; response to seveeral pollen antigens of ragweed correlate with expression of HLA class II allotype DRB1*1501
Term
What does HLA class II polymorphism involvement in IgE response to certain allergens suggest?
Definition
HLA class II:peptide combination predisposes to stimulation of Th2 response
Term
Can you test an individual's sensitivity to a particular allergen?
Definition
yes, it can be tested easily by observing a 2 step response
Term
What is the 1st step of the allergic response test?
Definition
injection of allergen into skin of a sensitive individual produces a chracteristic inflammatory reaction known as a wheal and flare at the injection site
Term
What is wheal and flare?
Definition
an immediate reaction (appearing within minutes) that is the result of mast cell-degranulation in the skin; released histamine and other mediators cause increased permeability of lcoal blood vessels (fluid enters tissue causing swelling or edema); swelling=wheal; increased blood flow causes redness=flare
Term
How long do immediate allergic reactions last?
Definition
30 minutes
Term
What is the 2nd step of the allergic response test?
Definition
6-8 hours post injection; a "late phase reaction" that occurs at the site of injection with more widespread swelling, mediated by leukotrienes, chemokines, and cytokines produced by mast cells following IgE mediated activation
Term
When reexposed to an allergen, what does the resulting Type I reaction depend upon?
Definition
when reexposed to an allergen, the resulting reaction depends upon tissues that come in contact with the allergen and only the mast cells residing at the site of allergen contact will be induced to degranulate (by IgE crosslinking with allergen)
Term
What are the various ways allergens gain access?
Definition
airborne and irritate mucose of respiratory tract; food borned and irritate mucosa of GI tract; gain access to connective tissue and blood via insect bites; gain access to blood via absorption via gut and respiratory mucosa
Term
What promotes degranulation?
Definition
crosslinking of allergen specific IgE bound to high affinity IgE receptor on mast cells
Term
What does degranulation of mast cells induce?
Definition
strong inflammatory response
Term
What is believed about IgE response?
Definition
evolved as a mechanism of defense against invertebrate parasites (worms); violent expulsion of airways (coughing and sneezing) and contents of stomach (vomiting) and intestines (diarrhea) initated by mast cells may have develops as a means of expulsion of parasites from body
Term
What is systemic anaphylaxis caused by?
Definition
allergens in the blood
Term
What is systemic anaphylaxis?
Definition
wide spread activation of mast cell degranulation causing both an incrase in vascular permeability and a widespread constriction of smooth muscle
Term
What is anaphylactic shock?
Definition
fluid leaving blood during systemic anaphylaxis causes dramatic reduction of blood pressure
Term
What happens to connective tissues during systemic anaphylaxis?
Definition
swelling due to influx of fluid
Term
What happens to organ systems during systemic anapylaxis?
Definition
damage can be sustained, impairing function
Term
What happens to airways/epiglottis during systemic anaphylaxis?
Definition
constriction of airways and swelling of epiglottis leading to asphyxiation/death (could result)
Term
How many deaths in the US from anaphylaxis?
Definition
160 per year
Term
How can potential allergens be intorduced directly into blood (systemic)?
Definition
insect sting; drug injections
Term
Can food or drugs taken orally incude anaphylaxis?
Definition
yes, if the allergen is absorbed rapidly from gut into blood; examples include peanuts and brazil nuts
Term
What is the most common cause of anaphylaxis?
Definition
IgE mediated allergy to penicillin or other drugs (ingestion or injection); 100 fatalities/year in US
Term
what are anaphalactoid reactions?
Definition
resemble anaphylactic reactions but do not involve interaction between allergen and IgE
Term
how do you treat anaphylactic and anaphalactoid reactions?
Definition
injection of epinephrine
Term
How does epinephrine work to help anaphylaxis?
Definition
stimulates reformation of tight junctions between endothlial cells, reducing the permeability of blood vessels, diminishing ttissue swelling, raising blood pressure; relaxes bronchial constriction and stimulates heart
Term
What should patients with anaphylactic sensitivity carry?
Definition
"epi-pen" (syringe full of epinephrine)
Term
What is rhinitis and asthma caused by?
Definition
inhaled allergens
Term
What is hay fever?
Definition
allergic rhinitis- mile allergic response chracterized by violent bursts of sneezing and runny nose in response to inhaled allergens
Term
What is allergic rhinitis caused by?
Definition
allergens diffusing across mucous membranes of nasal passages and activating mucosal mast cells beneath the nasal epithelium
Term
What characterizes allergic rhinitis?
Definition
local edema obstructing nasal airways + nasal dischrage of eosinophil-rich mucus; histamine release that causes general irritation of nasal passages
Term
What are secondary allergic rhinitis symptoms?
Definition
reaction can extend to ear/thraod leading to accumulation of fluid in sinuses and Eustachian tubes (conducive to bacterial infection) and conjunctiva of eye (allergic conjunctivitis)
Term
What is allergic asthma?
Definition
more serious condition than allergic rhinitis; when commonly inhaled allergens cause chronic breathing difficulties
Term
How is allergic asthma triggered?
Definition
when allergen/IgE interaction stimulates submucosal mast cells in lower respiratory tract
Term
What characterizes allergic asthma?
Definition
increase in fluid and mucus secretions into respiratory tract; bronchial constriction due to contraction of smooth muscle surrounding airways; chronic inflammation of airways involving persistent infiltration of leukocytes (Th2, eosinophils, neutrophils)
Term
What is the overall effect of allergic asthmatic attack?
Definition
trapping of air in the lungs making breathing more difficult (can be fatal)
Term
What is unique about allergic asthma?
Definition
initally driven by response to an allergen but chronic inflammation that develops can be perptuated in absence of further allergen
Term
What can almost totally occlude the airways in allergic asthma?
Definition
mucus plugs
Term
What develops in the airways in allergic asthma?
Definition
generalized hypersenstivity; chemical irritants that are commonly present in air (cigarette smoke, sulfur dioxide) can trigger attacks
Term
What can exacerbate asthmatic disease?
Definition
immune responses to bacterial or viral infection of respiratory tract, especially infection that elicit Th2 responses
Term
What is chronic asthma considered?
Definition
Type IV hypersenstivity
Term
What is urticaria?
Definition
hives; itchy swellings caused by release of histamine by mast cells in the skin, following activation by allergen; reaction is essentially a wheal and flare
Term
What is angioedema?
Definition
inflammation caused by activation by activation of mast cells in deep subcutaneous tissue; swelling is more diffusie than observed for utricaria
Term
What causes both urticaria and angioedema?
Definition
food or drug allergens carried to the skin via bloodstream; can occur during anaphylactic reaction
Term
What can food allergies cause?
Definition
systemic effects and gut reactions
Term
What is interesting about humans and their foodstuffs?
Definition
humans eat a wider variety of "foodstuffs" than other living things; food is composed of a number of different proteins (many potentailly immunogenic) but only a few proteins ilicit IgE Ab responses
Term
What foods cause food allergens (typically)?
Definition
grains, nuts, fruits, elgumes, fish, shellfish, eggs, milk
Term
What happens once a person is sensitized to a food allergen?
Definition
subsequent intake of that allergen leads to an immediate reaction in the GI tract
Term
What do food allergens do in the gut?
Definition
pass through wall of gut, bind to IgE on mast cells of GI tract, triggering degranulation
Term
What does histamine in food allergen/mast cell reaction do?
Definition
causes increase in permeability of blood vessels, leading to accumulation of fluid in gut lumen
Term
What do smooth muscles of stomach walls do in food allergen sensitivity? The itestine?
Definition
contract, producing cramps and vomiting; same reaction in intestine, causing diarrhea
Term
How can you treat/prevent allergic reactions?
Definition
modification of behavior; pharmacological; immunological
Term
Describe modificaiton of behavior to preventing allergies?
Definition
modify patient's behavior and/or environment to eliminate contact with allergen
Term
Describe the pharmacological approach to treating/preventing allergies?
Definition
use drugs that reduce impact of allergen contact; drugs that block effector pathways of allergic response and limit inflammation
Term
What are some examples of anti-allergy drugs?
Definition
antihistamines; corticosteroirds; cromolyn sulfate; epinephrine
Term
What do antihistamines do?
Definition
reduce rhinitis and urticaria by preventing histamine from binding to H1 histamine receptors on vascular endothelium
Term
What do corticosteroids do in anti-allergy treatment?
Definition
suppresses leukocyte function; treat chronic inflammation of asthma, rhinitis, eczema
Term
What does cromolyn sulfate do in anti-allergy treamtnt?
Definition
prophylactic inhalant; prevents degranulation of activated mast cells and granulocytes
Term
What does epinephrine do in anti-allergy treatment?
Definition
reverese anaphylaxis
Term
What does immunological treatment of allergies do?
Definition
prevents production of allergen specific IgE; modules immune resonse so that it shift from an IgE response to an IgG response
Term
Describe some of the immunological strategies for anti-allergy treatment.
Definition
1) desensitization: series of injections of increasing doses of the allergen; gradulaly changes a Th2 (IgE) response to a Th1 respone in which no IgE is produced; can reuslt in anaphylaxis so be careful; 2) vaccinte patients with allergen derived peptides known to be presented by HLA class II molecules to Th2 CD4 cells in an attempt to induce anergy
Term
What is unique about people who experience parasite infections?
Definition
rare develop allergic disease
Term
Why might people infected with parasites rarely develop allergic disease?
Definition
parasites induce very potent imune responses that are typically Th2 driven and produce large quantities of IgE
Term
How much IgE is parasite-specific?
Definition
small percentage
Term
What is true of the remainder of the IgE (that which is not parasite specific)?
Definition
highly heterogenous and represents product of non-specific polyclonal B and T cell activation by parasite
Term
What does nonspecific IgE dO?
Definition
outcompetes the parasite specific IgE for binding to high affinity IgE receptor on mast cells, basophils, and eosinophils (strtegy prevents parsite from triggering IgE mediated effector mechanisms, allowing parasite to evade immune response)
Term
What is a byproduct of the parasitic strategy to evade immune response?
Definition
people living in regions with high incidence of parasitic infections (and high concentrations of IgE experience reduced incidence of allergic disease compared to people that live in areas with low incidence of parasitic infections)
Term
What is type II hypersenstiivy?
Definition
reactions caused by antibodies specific for altered components of human cells
Term
What are some common examples of type II hypersensitivity reactions?
Definition
hemolytic anemia and thrombocytopenia (caused by destruction of red blood cells or platelets, respecitvely), following the administration of a drugs
Term
What can type II hypersenstiivty reactions be associated with?
Definition
Adminstration of drugs penicillin, quinidine (treats cardiac arrhythmia) and methyldopa (treats high blood prssure)
Term
What do the drugs do in Type II hypersensitivity reactions?
Definition
chemically active drugs bind to surface of red blood cells or platelets and create new epitopes to which immune system is not tolerant
Term
What happens in penicillin induced type II hypersensitivity?
Definition
new epitopes generated by penicillin stimulate production of IgM and IgG antibody specific for new epitopes; penicillin-modified RBCs must be coated with complement which facilitates phagocytosis by macrophages via complement receptors
Term
What is a side effect of complement activation by infection being treated with penicillin?
Definition
penicillin=modified RBCs must be coated with complement
Term
What do macrophages do in pencillin induced type II?
Definition
present newly formed epitopes to naïve CD4 T cells to produced armed effector Th2 cells
Term
What do effector Th2 cells do in penicillin induced type II?
Definition
those that are specific for new epitopes supply help to antigen-specific B cells, IgG specific for new epitopes is produced
Term
What do the IgG antibodies do in penicillin induced type II?
Definition
bind to altered RBCs and stimulate either complement activation or phagcytosis by macrophages
Term
What is the end result of penicillin induced type II?
Definition
altered RBCs are destroyed (lysed, phagocytosed)
Term
What causes type III hypersenstivity reactions?
Definition
immune complexes formed from IgG and soluble antigens
Term
When are antigen:antibody complexes generated?
Definition
in almost all immune responses (in most cases, they are cleared without causing tissue damage)
Term
What is the size of immune complexes?
Definition
very small (single complex of 1 antigen molecule and 1 Ab molecule) or very large (containing milions of each)
Term
What is true of large immune complexes?
Definition
they fix complement efficiently and are readily taken up by macrophages and removed without incident
Term
What is true of smaller immune complexes ?
Definition
less efficient at complement fixing; tend to remain in circulation and become deposited in blood vessel walls
Term
When does tissue damage (type III) occur?
Definition
whne sufficient immune complexes accumulate
Term
What happens once immune complexes accumulate?
Definition
circulating leukocytes recognize the immune complexes through their Fc and complement receptors, activating their inflammatory activities
Term
What is the Arthus reaction?
Definition
inflammtory response caused by antigen-specific IgG diffusing from blood into injection site tissues and combining with soluble antigen to form immune complexes and activating complement
Term
What causes systemic type III reactions?
Definition
caused by IV administration of large quantities of antigen
Term
What is serum sickness?
Definition
results from immune response to non-self material administered into bloodstream as treatment for a variety of illnesses
Term
What causes serum sickness?
Definition
systemic accumulation of immune complexes and eventual systemic inflammatory responses
Term
What characterizes serum sickness?
Definition
chills, fever, rash, arthritis, vasculitis, sometimes glomerulonephritis
Term
What are some examplse of serum sickness?
Definition
immune horse sera injected into patients to treat life-threatening bacterial infections such as diphtheria, tetanus, scarlet fever; monoclonal anti-T cell Ab in large doses to transplant patients to prevent rejection; large injections of bacterial enzyme streptokinase to degrade blood clots in heart attack patients; large IV injections of penicillin, even in people not allergic to pencillin- causes alteration of RBCs, eliciting Ab responses
Term
How else can type III hypersenstivity be caused?
Definition
continual inhalation of antigens that elicit IgG instead of IgE antibody reponses
Term
What does continued inhalation of antigens do?
Definition
accumulation of immune complexes in walls of lung alveoli, leading to inflammatory responses
Term
What does inflammation in lungs from continued antigen inhalation lead to?
Definition
accumulation of fluid, antigen, immune cells that prevent proper lung function
Term
What people are at risk for inhaled antigen diseases of Type III variety?
Definition
workers exposed daily to same airborne antigens; farmers; bird breeders
Term
What is farmer's lung?
Definition
type III condition describing constant exposrue to ahy dust and mold spores
Term
What is bird breeder's disease?
Definition
another common type III hypersensitivity disease of lungs caused by inhalation of avian antigens
Term
What is Type IV hypersensitivity?
Definition
reactions mediated by antigen specific effector T cells
Term
What is another term for type IV?
Definition
delayed type hypersensitivity (DTH)
Term
Why are DTH called "delayed?"
Definition
occur 1-3 days after contact with antigen in stark contrast to Ab mediated hypersensitivites which are usually apparent within minutes of antigen exposure
Term
How much antigen is required in DTH and why?
Definition
100-1000 fold larger quantities due to relative inefficiency of antigen processing/presentation
Term
What are the most common antigens eliciting DTH responses?
Definition
mycobacterial proteins, insect venoms, penadecacatechol (poison ivy), small metal ions
Term
What is the most well studied example of Type IV?
Definition
tuberculin reaction- clinical test to determine if a person has been infected with Mycobacteria tuberculosis
Term
How do you perform the tuberculin test?
Definition
small amount of protein from M. tuberculosis is injected subQ
Term
What happens in an individual who has been exposed to TB (they have produced immune response previously)?
Definition
he/she produces an inflammatory reaction around the site of injection 24-72 hours post-injection
Term
What mediates the inflammatory response in tuberculin test?
Definition
effector Th1 cells that recognize pepties (presented by MHC class II on macrophages) derived from injected protein; cells produce cytokines that activate and recruit macrophages to the site
Term
What is poison ivy?
Definition
term used to describe type IV hypersenstivity reaction produced against penadecacatechol (Pchol)
Term
What is Pchol?
Definition
small, highly reactive lipid-like molecule that is present in the roots and leaves of North American "poison ivy" plant, Rhus toxicodendron
Term
What happens upon initial contact with the poison ivy plant?
Definition
Pchol penetrates outer layers of skin and indiscriminately forms covalent bonds with extracellular proteins and skin cell surface proteins, forming new antigens that are recognized as non-self;local APCs (macrophages and Langerhans cells) take up new antigens, return to secondary lymphoid tissue, and prsent peptide antigens on MHC class II to naive CD4 cells
Term
What happens as a result of Pchol's ability to penetrate cell membranes and modify intracellular proteins?
Definition
modified proteins can be processed and presented via MHC class I molecules to naïve CD8 cells as well
Term
What happens in initial contact with poison ivy?
Definition
production of effector T cells and immunological memory but little if any inflammatory resopnse
Term
What happens in subsequent contact with poison ivy plants?
Definition
unpleasant rash of skin mediated by antigen-speicfic effector CTLs (kill cells exposed to Pchol) and antigen-specific effector Th1 cells that produce cytokines that activate macrophages and induce inflammation
Term
What is poison ivy an example of ?
Definition
contact sensitivity because contact of allergen with skin is required to initiate allergic response
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