ABSTRACT
B lymphocyte can change the class of antibody being expressed by moving a new C gene segment into position after the recombined VDJ segment, deleting the intervening deoxyribonucleic acid (DNA). The new heavy chain has a different constant region but retains the same antigen-binding specificity of the previous heavy chain. In the germ-line, each light chain gene exists as multiple V and J gene segments upstream of a single C gene segment. During B-lymphocyte differentiation, one V gene segment joins with one J gene segment to assemble the complete light chain gene, usually by deletion of intervening DNA. During maturation of the B lymphocyte, the V and C region DNAs are moved next to each other and are joined together to create a functioning light chain gene. This somatic recombination usually occurs by deletion of the DNA between the germ-line V and C regions but can also occur in some cases by an inversion mechanism.
