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Combinatorial joining of gene segments
The joining of gene segments to form the components for Ig receptors.
Human kappa receptor formation
DNA has various V (variable) and J (joining) regions.
1) Transcription causes specific V, J and C (constant) region to come together.
2) RNA splicing removes excess RNA.
3) Translation produces light chain.
Heavy chain receptor formation
V, D, and J region.
1) D and J form first, and then V joins DJ.
2) 51 V, 6 J, and 27 D different genes.
During joining of antibody gene fragments, nucleotides are lost from the ends of recombining gene fragments. Insertions can happen too.
6 alleles total, 3 from paternal and 3 from maternal.
Only two will be activated and the others will not be used during B cell development.
B cell development
1) Combinatorial joining of gene segments.
2) Junctional diversification during joining of gene segments.
3) Combinatorial joining of light/heavy chains (allelic exclusion).
4) Somatic hypermutation
- 1) Antigen-specific.
- 2) Defend vertebrates against infection.
- 3) Membrane bound receptors and never secreted.
- 1) Heterodimer of a and b chain
- 2) Each chain has 2 Ig like domain
- 3) Each chain encoded by V, D, and K
- 4) No somatic hypermutation.
- 5) Low binding affinity (Ka ~10^6 L/mol).
Cytotoxic T cell
Directly kill cells infected with pathogen.
Helper T cells
Stimulate response of others such as macrophages, B cells, and Tc.
T cell responses vs. B cell responses
1) Once T cell activated to become effector cells, they act only at short range with target cell and either kill or signal.
2) Antigen causes proliferation only when it is displayed by antigen-presenting cells.
Antigen presenting cells in lymphoid organs
- 1) Dendritic cells (innate)
- 2) Macrophages (innate)
- 3) B cells (humoral)