Abstract
The germinal center is a unique site of the lymphoid tissues where positive selection of B cells takes place in response to T-cell-dependent antigens, resulting in apoptosis of a large number of B cells. Although various molecules have been reported to be involved in this selection, only a few comprehensive studies have been performed in terms of apoptosis-related molecules implicated in apoptosis of germinal center B cells. In this review, we mention the expression of apoptosis-related molecules in the germinal centers, based on our own data especially focusing on Bcl-2 family proteins. In contrast to an antiapoptotic protein, Bcl-2, which was strongly expressed in mantle cells, but absent in most germinal center B cells, the other antiapoptotic proteins, Bcl-XL and Mcl-1, and the death-inducer proteins, Bax and Bak, were expressed in germinal center B cells. This expression pattern was comparable to that of Fas and CPP-32 (caspase-3). These results suggest that apoptosis of germinal center B cells is regulated by the concerted action of Bcl-2 family proteins and other apoptosis-related molecules including Fas and that the balance between antiapoptotic and death-inducer proteins caused by homodimerization and heterodimerization is important.
