B cell growth factor and T cell growth factor produced by mitogen-stimulated normal human peripheral blood T lymphocytes are distinct molecules.

Using a recently described assay for inducing and measuring the proliferation of normal human B cells in the absence of differentiation, we have demonstrated that B cell growth factor (BCGF) activity can be obtained from the culture of human peripheral blood mononuclear cells in the presence of mitogens. Using Sephacryl S-200 gel filtration, BCGF activity was demonstrated in the 20 to 30K m.w. fractions of mitogen-stimulated peripheral blood mononuclear cells. However, this fraction also showed substantial T cell growth factor (TCGF) activity. Despite this overlapping of m.w., BCGF activity could clearly be separated from TCGF activity by selective absorption of factor-containing supernatants with the interleukin 2 activity by using interleukin 2-dependent cells without any diminution of BCGF activity, strongly suggesting that these two factors may be distinct molecular entities.