B-cell growth factor: distinction from T-cell growth factor and B-cell maturation factor.

A T-cell hybridoma was derived by somatic cell hybridization between concanavalin A-activated BALB/c spleen cells and the AKR thymoma BW 5147. Media conditioned by hybridoma cells, even at high dilutions (1:1,000) support the growth of lipopolysaccharide-stimulated B-cell blasts but not that of T-cell growth factor (TCGF)-reactive T-cells. This activity, herein designated B-cell growth factor (BCGF), has a Mr of approximately equal to 20,000 and it can readily be separated from TCGF (Mr approximately equal to 30,000) by gel filtration. BCGF is constitutively produced by the hybridoma cells, it is removed from conditioned media by incubation with target cells at +4 degrees C, and it is equally effective on B-cell blasts carrying different major histocompatibility complex and Ig haplotypes. BCGF shows no T-cell replacing factor (TRF) activity, and it is poor in supporting the development of Ig-secreting plaque-forming cells in B-cell blast cultures. Terminal maturation, however, can be induced in BCGF-dependent blasts by addition of conditioned media from normal helper T cell cultures, suggesting that two distinct factors are involved in the helper cell-dependent growth and maturation of B lymphocytes.