Summary Chapter 4

Immunology Chapter 4 – Antibody structure and the generation of
B-cell diversity
Lines of defense
1. Barriers (chapter 2)
2. Innate immune system (chapter 2/3)
3. Adaptive immune system  in this chapter
a. B-cell
b. T-cell

Pathogens
1. Extracellular pathogens (bacteria): handled by proteins
that can stick to them
o Innate immune system: complement system
o Adaptive immune system: antibodies that are
produced by B-cells
2. Intracellular pathogens (virus): handled by killing the whole cell
o Innate immune system: NK cells
o Adaptive immune system: Cytotoxic T cell

The helper T-cells will help the B- and T-cell response.

The big difference between B- and T-cells
 B cell receptor: recognize intact antigens (proteins, carbohydrates, DNA)
 T cell receptor: recognize process (small) antigen that is presented in
MHC by dendritic cell

 B cell: recognition and effector molecules (plasma cells) are identical:
BCR-antibody
 T cell: recognition and effector molecules (cytokines) are different:
TCR-cytokines

The structure of antibodies
5 classes of antibodies differ in their constant region
1. Immunoglobulin G (IgG): most common antibody
a. 4 different subclasses (IgG1- IgG4)
2. Immunoglobulin M (IgM)
Extra domain in constant region and less flexible hinge region
3. Immunoglobulin D (IgD)
4. Immunoglobulin A (IgA)
a. 2 different subclasses (IgA1-IgA2)
5. Immunoglobulin E (IgE)
Extra domain in constant region and less flexible hinge
region

Structure:
- Constant region: close to the membrane
- Variable region: on the top – antigen-biding site. Every
TCR/BCR is different in variable region.
3 variable regions which have high variation in
sequence: