B-1 lymphocytes in mice and nonhuman primates.

B-1 cells comprise subpopulations of B lymphocytes in mice that display developmental, phenotypic, and functional characteristics that are distinct from those of conventional B cell populations (B-2 cells). Despite the known importance of murine B-1a (CD5(+) ) and B-1b (CD5(-) ) cells in the production of natural antibodies and rapid antigen-specific humoral responses to infection, evidence for B-1 cells in primates, including humans, is very limited. Identifying these cells in humans proves challenging given the limited number of cells that can be obtained from sites expected to harbor increased frequencies of these cells (i.e., peritoneal and pleural cavities) and the need to perform functional analyses on these cells, which, in the case of B-1b cells, must be carried out in vivo. My laboratory has used cynomolgus macaques and African green monkeys to bypass these limitations and to identify and extensively analyze primate B cell populations with the phenotypic and functional characteristics of mouse B-1a and B-1b cells. Our results reveal striking similarities between primate and murine B-1 cells, including a conserved functional role for primate B-1b-like cells in immunity to T cell-independent type 2 antigens.