Humoral Immunity

Question 1

How do B cells in the blood and in the lymph enter into 2ndary lymphoid tissue?

Answer 1

B cells in the blood enter through HEV and cells from the lymph enter through the subcapsular sinus

Question 2

What is the process by which antigens moving through the lymph are captured and presented to B cells in the lymph nodes?

Answer 2

Antigens are caught by specialized macrophages in the subcapsular sinus; capture is mediated by the antigen being coated with complement fragments which macrophages and follicular dendritic cells have receptors for

Question 3

What complement receptors are found on follicular dendritic cells and what are their ligands?

Answer 3

CR1- C3b; CR2,3,4- iC3b; CR2 also C3dg

Question 4

How does a B cell that enters a lymph node from the blod travel through the node?

Answer 4

Enters through HEV into the T cell zone and then move into a B cell zone (follicle)

Question 5

What attracts naive B cells to follicles?

Answer 5

B cell express CXCR5 which is attracted to CXCL-13

Question 6

How is a B cell activated by strictly antigen?

Answer 6

Cross linking over numerous (at least 2) BCR

Question 7

What are the 3 principal functions of the BCR?

Answer 7

1) Recognition and binding of pathogen 2) Intracellular signaling for activation 3) Internalization of the antigen for processing and presentation via MHC II

Question 8

What are thymus-independent antigens? What is a common example?

Answer 8

They are antigens that can generate an antibody response without T cell co-activation of the B cell; Usually highly repetative determinants (e.g., polysaccharides of bacterial coat) that can bind to very many BCR and amplify the signal

Question 9

What are the two signals required for B cell activation with thymus-dependent antigens?

Answer 9

1) cross-linking of BCR and 2) CD40 and CD40L ligation [Interactions between the MHC and TCR also augment the activation signal

Question 10

How do B cells and Tfh cells move from their respective areas in the lymph node to one another

Answer 10

Signal 1 of BCR activation induces CCR7 expression on the B cell drawing it to the CCL19, CCL21 gradient in the T cell zone; Tfh cells activated by dendritic cells reduce their expression of CCR7

Question 11

What results from full activation of a B cell in a lymph node?

Answer 11

Formation of a germinal center

Question 12

What is the process of affinity maturation?

Answer 12

The process by which an activated B cell undergoes somatic hypermutation in which there is rapid proliferation, producing clones that can have mutations in the antigen binding site which improve or decrease the affinity. Those clones with improved affinity continue to die, but the decreased affinity clones die such that the resulting population has a higher and higher affinity to the antigen

Question 13

What is the cause of X-linked Hyper IgM?

Answer 13

CD40L deficiency

Question 14

What is the intermediate stage between activated B cells and plasma cells?

Answer 14

Plasmablasts

Question 15

Where does terminal differentiation of plasmablasts to plasma cells occur?

Answer 15

In the tissue

Question 16

Where are the majority of serum antibodies produced?

Answer 16

Plasma cells living in the bone marrow

Question 17

What is the approximate length of time after a primary infection that a antibody can be measured in the serum? At what time point does the production peak?

Answer 17

1 week ; 2 weeks

Question 18

Which portion of the antibody confers effector function?

Answer 18

Fc region

Question 19

How does a neutralizing antibody work? Which classes are the best neutralizers?

Answer 19

The Ab binds to the outer surface determinant that is required by the pathogen (or toxin) to enter the cell; IgA, IgG, and IgM

Question 20

How do antibodies facilitate the elimination of soluble immune complexes? Which Ab classes are used for this?

Answer 20

Antibody:antigen complexes form and complement deposition occurs due to the affinity of Cb3 to the Fc portion of IgG or IgM. RBCs express CR1 which binds the C3b and transports the connected IC to Kupffer cells for phagocytosis

Question 21

Which Ab classes are best at fixing complement? Why?

Answer 21

IgG and IgM- They have a C1q binding site on their Fc portion

Question 22

Which Ab classes are best at Opsonization?

Answer 22

IgA or IgG

Question 23

Which Ab class is used against parasites? How does it work?

Answer 23

IgE Fc portion binds to FceR on eosinophils and binding triggers degranulation

Question 24

Which cells are always coated with noncomplexed IgE and why? How are these cells activated?

Answer 24

Mast cells and basophils because they express high affinity FceR; Activated by cross-linking the IgE

Question 25

What is immunological ADCC?

Answer 25

Antibody-dependent cellular cytotoxicity by NK cells

Question 26

What is the process by which ADCC occurs?

Answer 26

An infected cell expresses a pathogenic antigen that is recognized by and binds to IgG; Cross-linking of the Fc(gamma) receptors overrides the NK cell brakes and they destroy the IgG bound host

Question 27

How do NK cells kill?

Answer 27

Release of perforin and granzymes

Question 28

What is the mechanism by which Rituximab works?

Answer 28

Rituximab is a IgG MOAb against CD20 (on B cell lymphoma)which activates NK cell Fcgamma receptors and kills the cancer cells

Question 29

Which cells are considered most important for Fc-mediated destruction of bacteria?

Answer 29

Macrophages/monocytes and neutrophils

Question 30

Which cells are considered most important for Fc-mediated destruction of parasites?

Answer 30

Eosinophils, Mast cells, and basophils

Question 31

Which cells are considered most important for Fc-mediated destruction of virus-infected cells?

Answer 31

NK cells

Question 32

What is the function of FcRn?

Answer 32

Transports maternal IgG across the placenta to the fetus

Question 33

What is the function of pIgR?

Answer 33

Transportation o dimeric IgA antibodies acrocc epithelial barriers and into secretions

Question 34

What is the most prevalent form of Ig in breast milk?

Answer 34

IgA