- The B stands for Bursa of Fabricius and not bone marrow
- Expression of B-cell receptor genes
- Membrane-bound immunoglobulins serve the receptor functions
- Some B cells will become memory cells after any given encounter
- The memory cells will then escalate to the next immunoglobulin type the next time they are exposed to the same antigen
B Cell receptors
- aka BCR
- B Cells recognize antigens in their natural form through the surface antigen receptors known as B cell receptors
- Each receptor consists of a recognition, signaling, and coreceptor unit
- Essentially a membrane-bound immunoglobulin
- Has the same structure as immunoglobulins
- Recognizes structures known as antigenic determinants or epitope
- Recognition involves hydrogen bonding between CD3 of the immunoglobulin and the antigen epitope
- Includes at least two types of chains: Igα and Igβ
- A molecular complex formed by CR2 (binds complement components), CD19 (binds intracellular signaling molecules), and TAPA-1 (function unknown) molecules
- The construction of the heavy and light chains always happens sequentially (Heavy, then light).
- This is done so that the molecule ends up with only one specificity
- This is called allelic exclusion -- making sure that only one specificity is expressed
- Also see Janeway Figures 7.1, 7.3, 7.5, 7.14, 7.18, 7.25, 7.26, 7.37, 7.40, 7.45
- First part of cell development
- Joins VH - DH - JHand then tests to see if the strands check out.
- Once joined, VHDHJH is then joined to Cμ, which is then also tested.
- Once the heavy chain is validated, the light chain is formed
- Joins a Vlightκ to Jlightκ, then to Lκ
- Once the κ light chain is constructed, then the heavy λ chain will be constructed
- This is why there is always more variation in κ light chains than in λ light chains
- There is always a number of cells that express antibodies against self -- a screw-up in development
- Somatic hypermutation - aims to increase the affinity of immunoglobulins.
- Called somatic because it is not in the germ line (e.g. does not occur during development)
- If a B cell does not see an antigen in three days, then the B cell dies
- If it does see an antigen, then clonal selection begins