Humoral Immunity

Question 1

B Cells & Non-Protein Antigens

Answer 1

Naive B cells can directly bind to non-protein antigens and proliferate and differentiate into plasma cells.

• Polysaccharides and lipids stimulate IgM synthesis.

Question 2

B Cells & Protein Antigens

Answer 2

Naive B cells can directly bind to protein antigens but needs CD4+ T cells for full activation to produce other antibodies (IgG, IgA, IgE).

Question 3

Isotype Switching

Answer 3

Making different antibodies all with the same specificity.

• IgM –> IgG, IgA, or IgE

Question 4

Affinity Maturation

Answer 4

Helper T cells stimulate the production of antibodies with higher affinity for the antigen.

• Only occurs when antigen is peptide since CD4+ T cell (requires MHC II+peptide) is needed for affinity maturation.

Question 5

Antibody Structure

Answer 5

Fab Region: Antigen binding fragment

Fc Region: Crystallizable fragment
- Phagocytic cells, NK cells, and other inflammatory leukocytes have Fc receptors and can bind to Fc region on Immunoglobulin.

Question 6

IgA

Answer 6

Found in body surfaces that are exposed to outside world (such as nose, respiratory tract, GI tract, ears, eyes, and vagina).

• can transport across epithelium.
• two forms: monomer & dimer (secreted form)

Question 7

IgG

Answer 7

Found in all Body fluids and is most common. IgG functions in opsonization.

• IgG is the only antibody that can cross the placenta to protect the fetus and diffuse into extravascular site (extracellular space).

Question 8

IgM

Answer 8

Found in blood and lymph fluid and is largest in size.

• First type of antibody made in response to an infection; activate complement system
• two forms: monomer & pentamer (secreted form)

Question 9

IgE

Answer 9

Found in the lungs, skin, mucous membranes.

• Involved in allergic reactions (high in ppl with allergies).

Question 10

IgD

Answer 10

Found on the surface of newly matured B cells.

Question 11

What are 3 types of Mature B Cells?

Answer 11

1. Follicular B Cells
2. Marginal Zone B Cells
3. B-1 Lymphocytes

Question 12

What is Follicular B Cells?

Answer 12

Mature B Cells found in lymph node and spleen FOLLICLES.

• Follicular B Cells are the APC B Cells that present MHC II + peptides to CD4 T cells.

Question 13

What is Marginal Zone B Cells?

Answer 13

Mature B Cells found at the MARGINS of splenic follicles.

Question 14

What is B-1 Lymphocytes?

Answer 14

Mature B cells in lymphoid organs and peritoneal cavity that develop from a different progenitors of follicular B cells.

Question 15

Separate Zones for B vs. T Cells in Lymph Nodes

Answer 15

B Cells are in the cortex region (where follicles are)

T Cells are in the paracortex region (inner side of lymph node)

Question 16

How does complement system helps in B-Cell Activation?

Answer 16

C3d (a breakdown product of C3b) binds B cell at CR2 receptor to enhance B cell activation.

Question 17

What is CD40 ligand?

Answer 17

It is a protein presented on “activated” CD4+ T Cell that activates B Cells through secreted cytokines.

Question 18

Where does actual proliferation and differentiation of B and T cells Occur?

Answer 18

Germinal Center within the lymphoid follicle

Question 19

CD4+ T Cells & B Cell Class Switching

Answer 19

• Non-protein antigen –> IGM
• Th1 –> IgG
• Th2–> IgE
• Th17 –> IgA