| Themes > Science > Life Sciences > General Biology > Immunology > Recognition Systems in Immunity > Antigen Recognition: B Cells and Antibodies > B cell development |
B cell development in mammals takes place in the bone marrow. When B cells develop from their precursors they initiate a programme of differentiation which leads to rearrangement of the heavy chain gene segments. In order to allow the cell to test the functional integrity of the rearranged gene (only 1/3 are "in-frame"), Pre-B cells express 2 single domain Ig-like protein of invariant sequence which substitute for the light chain. The formation of the complex of the mu heavy chain with these surrogate light chains somehow tells the cell to stop rearranging the heavy chain locus and start rearranging the kappa locus. Similarly if a successful light chain rearrangement is achieved and the light and heavy chains form a complete antibody then this complex tells the cell to stop rearranging light chains, thus ensuring that only a single specificity is produced (allelic exclusion). Correspondingly those developing B cell clones which fail to make a productive rearrangement at both one of their heavy chain alleles and a light chain locus will die. There are also mechanisms for ensuring the death of any newly produced B cells whose antibody reacts strongly with self proteins on the surface of host cells (self tolerance; see lecture 12). |
|
|