The B cell then divides and differentiates into plasma cells, which secrete antibodies, and memory cells, which are held in reserve until next appearance of antigen. L chains have 2 domains of 110 amino acids each, the variable region and the constant region. There are only a few different constant regions, but more variable regions than would fit in the genome. Needs mechanisms to create antibody diversity. In pre-B cell, DNA splicing joins one V with one J region.
Random mutations occur in hypervariable regions of the V regions.
The splicing and mutation mechanisms often lead to a defective protein. When this happens, the cell tries splicing the gene on the homologous chromosome. All H start out as IgM, but switch to IgG, IgA, etc. using a DNA splicing mechanism for the C region. Similar to Ig's, but only 1 antigen binding site. Two chains, alpha and beta, with V and C regions on each.