Blimp-1 is a 98 Kd protein containing five Kuppel-type zinc finger domains that confer sequence specific DNA binding. It has been postulated to be a master regulator of terminal B cell differentiation. In the BCL-1 lymphoma model of differentiation from mature B cells to plasma cells, ectopic expression of Blimp-1 is sufficient to cause terminal differentiation manifested by loss of surface immunoglobulin, IgM secretion, expression of syndecan-1 and cessation of cell division. Recently, it is reported that Blimp-1 is also involved in T cell differentiation and T cell homeostasis and suppression of IL-2 production.