• diagnosed with x-linked agammaglobulin
• treated with IV gammaglobulin

Antibodies are made up of variable and constant regions

In any given Ig molecule, the light chains are identical, as are the heavy chains?

CDR = complementarity determining regions =

epitope binding sites.

These are what physically contact antigenic epitopes

• Antibody immunoglobullins
• recognize macromolecules, proteins, polysaccharides, lipids, nucelic acids, small chemicals, and conformational and linear epitopes
• T-cell receptors
• recognize peptides displayed by MHC, and linear epitopes

• Ab immunos
• unique clonal specificity with greater than 10⁹ distinct specificities
• TCRs
• also unique clonal specificity
• even greater than 10¹¹ distinct specificities

• Ab Immunos
• mediated by variable V regions of heavy and light chains of membrane Ig
• TCRs
• mediated by variable V regions of alpha and beta chains

upside down "y"

slide 9

important for:

1. diagnosing infections and their stages
2. identifying B cell tumors
3. diagnosing immunodeficiencies

1. they are cell surface receptors for the Fc regions of antibodies
2. they are crucial for antibody-mediated opsonization
3. The most important FcRs are found on phagocytes, APCs, mast cells, and eosinophils

How are the different types of Abs and TCRs made? What catalyzes this process?

• Abs and TCRs result from the recombination of gene segments in lymphocytes. 
• This process is catalzed by V(DJ) recombinase

1. multiple V, D, J segment combination possibilities
2. multiple heavy chains (9 kinds) and light chains (2 kinds) [isotype combinations]
3. juncitonal (J) diversity
4. somatic hypermutation possible combinations (10¹⁴)

Slide 17

• What Ig expression takes place in the "mature" stage of B-cell development? 
• Where are mature B-cells found?
• Why are they still considered naive (virgin) at this point

• Membrane IgM and IgD are present on the B-cell's surface. 
• they are found in primary lymhoid follicles (thymus and bone marrow)
• they are still naive because they have YET to encounter and bind to an antigen

• Precursor T-cells travel from bone marrow to the thymus for development
• mature T-cells are made in the thymus, then travel to secondary lymphoid tissues

slide 19

Trace the path of T-cell maturation in the Thymus (answer is only the parts marked in red on slide 20).

Answer = total of 6 steps

1. Stem cell leads to
2. double negative CD4- and CD8- pro T-cell, leads to
3. double positive CD4+ and CD8+ immature T-cell, leads to
4. Positive selection, leads to
5. Mature, single positive, naive T-cell, which then
6. migrates to Thymic medulla and thence to the periphery. 

slide 20

Define the following characteristics with regards to a Primary antibody response?

• lag time after immunization
• peak response
• antibody isotype
• antibody affinitiy

• lag time after immunization = usualyl 5-10 days
• peak response = smaller response
• antibody isotype = usually IgM is greater than IgG
• antibody affinitiy = lower average affinity; more variable 

Define the following characteristics with regards to a Secondary antibody response?

• lag time after immunization
• peak response
• antibody isotype
• antibody affinitiy

• lag time after immunization = 1-3 days, shorter than primary Ab response
• peak response = larger than primary Ab response
• antibody isotype = relative increase in IgG, and sometimes an increase in IgA and or IgE as well (heavy chain isotype switching)
• antibody affinitiy = higher average affinity (affinity maturation)

slide 22

• proteins are greater than carbohydrates and lipids
• antigen is large
• route of immunization involves subcutaneous, intranasal, and intramuscular instead of intraperitoneal, IV, or oral

Conformational determinant/epitope binds to an antibody, causing the protein to denature, which causes the antibody to no longer bind to the protein.

An example are proteins. 

Slide24

• external linear determinant/epitope binds to an antibody, and continues to remain bound after the protein is denatured.
• example is bacterial cell wall

Slide 24

• called multivalent antigens
• common, since most antigens are multivalent

• multivalent antigen with different epitopes
• multivalent antigen with a repeated epitope

slide 25

True or False

"Antibody cross-reactivity can occur when antigens are shared or are structurally similar"

• To bind to an antibody, haptens must be coupled with a larger molecule, often a protein called a carrier (e.g. RBC)
• Haptens, with their carriers, can bind to both B and T cells

True or False?

"Haptens can bind to antibodies without assistance"

False

Haptens can’t provoke antibody responses by themselves. They need to be bound to a carrier molecule

1. Antigen recognition in the primary lymphoid follicle
2. clonal expansion via helper T-cells in the secondary lymphoid follicle-germinal center
3. differentiatio of B-cell into a "high-affinity Ig-expressing B cell"
4. further differentiation into a memory B-cell
5. Memory B-cell goes into the blood and lymphoid tissues for secondary responses

What are the phases of humoral immune response from a naive B-cell to a cell that induces "isotype switching" and "affinity maturation"? Where does these types of B-cells go?

1. Antigen recognition in the primary lymphoid follicle
2. clonal expansion via helper T-cells in the secondary lymphoid follicle-germinal center
3. differentiation of B cell into either an "IgG-expressing B cell" or a "high affinity Ig-expressing B cell"
4.  IgG expressing cell leads to a state of "isotype switching" 
5. High-affinity Ig-expressing B-cell leads to a state of "affinity maturation" (with high affinity IgG)
6. both types of B-cells proceed to secondary follice-germinal center

What are the phases of humoral immune response from a naive B-cell to a state of "antibody secretion"?

1. Antigen recognition in the primary lymphoid follicle
2. clonal expansion via helper T-cells in the secondary lymphoid follicle-germinal center
3. differentiation of B cell into antibody-secreting plasma cell, which induces "antibody secretion"

• What type of antibodies do follicular B cells have before and after a reaction with protein antigen+helper T-cell. 
• What do follicular B-cells become after ther reaction?

• before reaction = IgD, IgM
• after reaction = IgG, IgA, IgE (AGE acronym)
• after reaciton, follicular B-cells become isotype-switched, high affinity antibodies, and long-lived plasma cells

• before reaction = IgM antibodies present
• after reaction = mainly IgM antibodoes; short-lived plasma cells are also present

• before reaction = IgM and CD5 present
• after reaction = mainly IgM; also short-lived plasma cells

What is the relation of plasma cells to the following:

• surface Ig
• surface MHC class II
• high-rate Ig secretion

• surface Ig = not present on plasma cells
• surface MHC class II = not present on plasma cells
• high-rate Ig secretion = PRESENT on plasma cells

• TD antigens undergoe isotype switching (IgM to IgG and IgA, 
• TI antigens have little or no isotype switching (if any occurs, IgM forms some IgG)
• example of TD antigen are vaccines
• example of TI antigen are pneumococcal polysaccharides

slide #31

1. entry into cell and mitosis (clonal expansion)
2. increased expression of cytokine receptors (respond to cytokines produced by helper T-cells)
3. Low-level IgM seretion (early phase of humoral response)

With the help of helper T-cells, it undergoes a germinal center reaction and becomes activated and differentiates

slide #33

1. B-cell recognition of native protein antigen
2. receptor-mediated endocytosis of antigen
3. antigen processing and presentation
4. T-cell recognition of antigen

slide #34

B-cell APCs require interaction of 2 molecules and 2 cytokines from the T-cell in order to activate and class swtich

• molecules = CD40 & CD40L (ligand)
• cytokines = IL4 & IL5

slide #35

1. Where does somatic hypermutation take place?
2. What is somatic hypermutation's effect on the B-cell?

1. Somatic hypermutation occurs in germinal centers, not in TcRs.
2. Its a site for affinity maturation and diversity-generation after the B-cell has contacted the antigen. This increases B-cells' antibody-affinity for antigens, thus leading to production of only the best-binding antibodies

slide #36

With increasing immunizations, more mutations accrue in the V regions of B-cell antibodies.

This is accompanied by increasing affinity for antigens

slide #36

1. IgM, IgG (subclasses IgG1, IgG3), IgE, IgA [remember "AME G"
2. This changing process is called "class isotype switching"

slide #37

1. Fc receptor-dependent phagocyte responses; complement activation; neonatal immunity (remember babies say "gaga", so IgG)
2. its subclasses are IgG1, and IgG3

"E" for "evil", and evil is in "hell", so

IgE provides immunity from HELminths.

Also mast cell degranulation

1. What is IL4?
2. What is it's function
3. Which antibodies does it inhibit?
4. Which antibodies does it induce?
5. Which antibodies does it have no effect on?

1. IL4 is a cytokine released by T-helper cells
2. It stimulates class switching
3. Inhibits IgM, IgG3, & IgG2a
4. Induces IgG1 & IgE
5. No effect on IgG2b & IgA

1. What is IL5?
2. What is it's function
3. Which antibodies does it inhibit?
4. Which antibodies does it induce?
5. Which antibodies does it have no effect on?

1. IL5 is a T-helper cell-derived cytokine
2. induces Ab class switching
3. inhibits none
4. augments production of IgA
5. has no effect on IgM, IgG3, IgG1, IgG2a, IgG2b, and IgE

slide #39

Where are the following immunoglobulins distributed in the body?

• IgG
• IgM
• IgA
• IgE

• IgG = blood, tissues
• IgM = blood
• IgA = body cavities
• IgE = epithelial surfaces, gut, lung

• IgM pentamer is found in the blood
• IgA dimer is found in bodyily secretions, but not in blood
• Both are held together by "J chains"

• maternal antibodies protect them
• this process is called natural passive immunity

1. neutralization of microbe and toxins via phagoctyes
2. opsonization and phagocytosis of microbes via Fc-receptors
3. antibody-dependent cellular cytotoxicity via NK cell

slide #44

1. lysis of microbes
2. phagocytosis of microbes opsonized with complement fragments (e.g. C3b)
3. inflammation

1. block penetration of microbe through the epithelial barrier
2. block binding of microbe to cell surface, thus preventing infection
3. block binding of toxin to cellular receptor

1. How do antibodies prepare pathogens for phagocytosis?
2. How does the phagocyte bind to the pathogen?

1. Abs opsonize extracellular pathogens for phagocytosis
2. Phagocytes bind to the opsonized pathogen via the phagocytes Fc receptors

1. killing of the ingested microbe occurs by acidification, oxygen radicals, NO, defensins, and hydrolytics enzymes.

slide #46

1. IgE antibodies are bound to mast cells. 
2. multivalent antigen binds to, and crosslinks, IgEs on mast cell surface. 
3. crosslinking ativates mast cell, which causes the release of granule contents (histamine, inflammatory mediators)

1. Which antibody is on the surface of eosinophils?
2. How are eosinophils activated?
3. What is the effect of this activation on the microbe?

1. IgE antibodies are on the surface of eosinophils
2. eosinophils are activated by the binding of helminths to the IgE Abs, which also crosslinks them
3. this activation causes microbe (e.g. helminth) death

Memory B cells are more abundant and make higher affinity (i.e, “better”) antibodies than do naïve B cells

1. Igm binds to antigens on bacterial surface
2. C1q binds to IgM on bacterial surface.
3. This activates C1R, which initiates the Classical C pathway

• What catalyzes the Membrane Attack Complex (MAC) in the Classical C Pathway?
• What is the end effect of catalyzing MAC?

• MAC is catalyzed by C5b/C6/C7/C8

• Catalyzing MAC leads to lysis of the pathogen

C4b/C2b/C3b  or C3b/Bb cleaves C5 into C5a and C5b

How is C3b formed, and what are its contributions to the Complement C Pathway in dealing with microbes?

(4 steps)

1. C3b is formed by the cleaving of C3 into C3a and C3b via the C4b/C2a complex.
2. C3b then binds to microbe's surface
3. This binding forms MAC
4. MAC causes osmotic lysis of the microbe

C3b contributes to lysis of microbes int the Classical C Pathway.

1. What is this process called when C3b performs on its own?
2. What is this process called when C3b's functions are performed in concert with antibodies

1. On its own, C3b's function is known as "Complement-mediated cytolysis"
2. In concert with antibodies, the process is known as "Complement fixation"