Human B cell activating factor (BCAF): production by a human T cell tumor line.

In a previous study, we demonstrated that supernatants from human T cell clones stimulated by a pair of anti-CD2 monoclonal antibodies cause resting human B cells to become activated and to proliferate in the absence of any other signals. The activity responsible for these effects was shown to be different from already characterized lymphokines and in particular from IL-2 and IL-4, and was named B Cell Activating Factor or BCAF. In this paper, we describe the production of BCAF by a human T cell tumor line T687 after phorbol myristate acetate (PMA) stimulation; this production can be potentiated by phytohemagglutinin (PHA). We further show that the stimulatory phase can be separated from the secretory phase thereby avoiding contamination of BCAF-containing supernatant by PMA and PHA. Supernatants produced under these conditions do not contain either IL-4 or IFN but contain traces of lymphotoxin and 2 to 10 ng/ml of IL-2. The T687 cell line will allow us to obtain a large volume of supernatant for biochemical study and purification of the molecule(s) responsible for BCAF activity.