The normal thymus contains a small population of B cells; however, their origin and function has been rather unclear. In the Proceedings of the National Academy of Sciences, Huang and colleagues observe that those B cells develop from progenitors in the thymus with minimal contribution from the peripheral B cell pool. The thymic B cell population is phenotypically distinct from both follicular B cells and B-1 cells. Thymic B cells also have high expression of major histocompatibility complex class II and costimulatory molecules and are adept at antigen presentation. Thymic B cells are present at the cortico-medullary junction, which suggests that they may be involved in the negative selection of T cells. Indeed, through the use of a system with transgenic expression of BCRs and TCRs, the authors find that autoreactive B cells can contribute to the negative selection of T cells. Therefore, thymic B cells may be involved in 'pruning' certain subsets of autoreactive T cells.

Proc. Natl. Acad. Sci. USA (15 October 2013) doi:10.1073/pnas.1313001110