[Molecules involved in characteristics of naive/memory B cells]

Memory B cells, which carry immunoglobulin somatic hypermutations, generate immunoglobulins rapidly and vigorously in the secondary immune response. We recently highlighted studies confirming that CD27 surface antigen is a memory B-cell marker. By using the memory B-cell marker, peripheral blood B cells were clearly distinguished into naive and memory B cells. The B cells are further separated to three populations by the expressions of CD27 and IgD: IgD+CD27- naive B cells (circulating B cell 1: cB1), IgD+CD27+ unclass-switched memory B cells (cB2, so-called IgM memory B cells) and IgD-CD27+ class-switched memory B cells (cB3, switched memory B cells). Here we show molecules which are involved in characteristics of naive/memory B cells and their functions. This functionally distinct B cell subset and molecules involved in the subset may represent an important mechanism by which quiescent human B cells can initiate and propagate rapid and vigorous immune memory responses, and regulate the synthesis of low/high affinity antibodies.