Question

1. What if a mutation occured in a certain V segment, would it be bad for all B cells?

2. B cells are capable of allelic exclusion but how are we able to have cells with the same heavy chain but different light chains?

Answer 1

1. If a mutation occurs in a certain v segment, it will NOT be bad for all B cells.

For examole: point mutations induced by somatic hypermutation creates the diversity which is useful for selection of enhanced binding of antigen. This occurs only in mature B cells having rearranged V- region genes. The mutations only occurs in mature B cells therefore only mature B cells are affected.

2. The proces by which B cell actively rearranges one light chain and one heavy chain allele thus allowing to express one H and one L chain pairing in an antibody with one specificity is called allelic exclusion.

The proces of secondry rearrangement firstly removes the gene originally encoding the autoreactive light chain and then provides a newly arranged VL-JL l gene that encodes for a non-autoreactive L chain. Thus, providing a cell with same heavy chain but different light chain.