Innate B cell helpers reveal novel types of antibody responses.

Antibody responses are classified according to whether B cells receive help from T cells--that is, whether they are thymus-dependent (TD) responses or thymus-independent (TI) responses. The latter can be elicited by microbial ligands (TI type 1) or by extensive crosslinking of the B cell antigen receptor (BCR; TI type 2). The hallmark of a TD response is the induction of germinal centers in which follicular helper T cells (T(FH) cells) select B cells with somatically mutated high-affinity BCRs to become memory cells. Studies have shown that B cells can also receive innate TD help from natural killer T cells (NKT cells) and innate TI help from cells such as neutrophils but that the outcome of such help differs from conventional TD and TI responses. Here we update the classification of antibody responses to take into account these emerging types of B cell helpers.