Blimp-1 was initially identified as a zinc finger-containing protein that drives the maturation of B lymphocytes into immunoglobulin-secreting cells. Together with X-box-binding protein 1 (XBP1), Blimp-1 is induced upon terminal differentiation of plasma cells. The transcriptional repressor activity of Blimp-1 has also been found to regulate T cell homeostasis and function, possibly by suppressing the expression of the cytokines IL-2 and interferon-gamma during T cell development. More recent experiments have suggested that Blimp-1 also plays a major role in the formation of primordial germ cells (PGC) in developing mammalian embryos. In these experiments, Blimp-1-deficient mutant mouse embryos form a cluster of PGC-like cells which fail to show the expected migration, proliferation, and repression of homeobox genes that normally accompany specification of primordial germ cells. Blimp-1 exists as at least two different isoforms.