During the so-called immunoglobulin class-switching process, the heavy chain constant region changes while antigen specificity is maintained. Immunoglobulin class switch takes place within germinal centers contained within B-cell follicles of the secondary lymphoid organs. Another process that occurs within germinal centers is somatic hypermutation, which results in the sequential accumulation of point mutation in the Ig variable region gene. If the point mutations(s) result in increased binding affinity to the inducing antigen, the B-cell blasts (centrocytes) survive, proliferate, and eventually give rise to memory B cells and plasma cells that secrete high-affinity antibody (this process is called maturation). Through these processes, memory B cells are generated within germina centers.