B lymphocyte induced maturation protein-1 (Blimp-1) mRNA is induced upon antigen-dependent activation of both T and B lymphocytes, in spite of the fact that it plays very different roles in the two lineages. B cells have at least four different mechanisms to repress Blimp-1 and repression is relieved before induction. Only one repressor, Bcl-6, is known in T cells. Activators must also be present to induce Blimp-1 in both T and B cells. Cytokines IL-21, IL-10, and IL-6, activating STAT3, are crucial in B cells along with toll-like receptor (TLR) signals, whereas IL-2 is crucial in T cells. AP-1, NF-kappaB, and IRF4 also activate Blimp-1.