VETS2006 Lecture Notes - Lecture 7: B Cell, Immunoglobulin Light Chain, Antigen
B Cells
- B cells (B lymphocytes) are produced in the bone marrow
- They are found in the lymph nodes, spleen and the boone marrow.
- Small numbers of B cells circulate in the blood
- B cells have B cell receptors (BCR) on their surface. The BCR is almost identical to an
antibody molecule, but has a protein that anchors it to the cell.
B Cells and Antibodies
- The BCR on each B cell is specific for only one antigen (the cognate antigen)
- Each B cell has a different BCR, which recognizes and binds to one cognate antigen.
- Following activation, most B cells become plasma cells (antibody-producing factories)
- The atiody produed y a idividual plasa ell is idetial to the BCR o the paret B
cell, i.e. It will bind to the same cognate antigen.
B Cell and Antibody Diversity
- Individual animals have an enormous diversity of BCRs (10-100 million)
- This ensures that there will be a B cell with a specific BCR capable of responding to the
millions of different antigens an animal is exposed to during its lifetime
- The diversity of BCR (and the subsequnt antibody produced by the derived plasma cell) is
created during B cell development in bone marrow.
Immunoglobulin Gene Segments
- Variable regions of antibodies are encoded by 3 (heavy chain) or 2 (light chain) gene
segments (exons)
- Constant regions for light and heavy chains are each encoded by 1 exon.
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Generation of BCR diversity
- A aial’s geoe hroosoes otais ultiple opies of gee segets that ode
for the variable regions of the light and heavy chains.
- During development from bone marrow stem cells, a process of gene selection and deletion
occurs within each B cell.
- The results in a genetic sequence that codes for a unique BCR
- This unique BCR recognizes and binds to only one antigen (its cognate antigen)
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Light Chain Gene Rearrangement
- The process of gene rearrangement in light (L) chain gene segments occurs in the same
manner as for heavy chains.
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