Age (autoimmunity) associated B cells (ABCs) and their relatives

B cells affect human and animal health in numerous ways. They are the precursors for the antibody-secreting plasma cells and they also take up antigen, particularly antigen for which they bear-specific receptors, very efficiently and thus present antigen to T cells. The T cell–B cell interactions that thus occur serve not only to affect the B cell, but also, the T cell partner of the interaction. B cells are known to be quite heterogeneous. The different subpopulations of B cells contribute to different types of immune responses. Over the last 20 years it has become apparent that some B cells unexpectedly express a transcription factor, T-bet (Tbx21) that is conventionally associated with T cells. B cells expressing T-bet have been found in elderly female mice, in humans and mice infected with many different types of organisms, and in autoimmune mice. Where examined, the T-bet expressing B cells, or related cells, affect the course of the disease. For example, in patients of mice with autoimmunity the T-bet positive B cells, and their relatives, are the precursors for autoantibody production. Here we discuss the heterogeneity of T-bet expressing B cells and related cells.