Proliferation and differentiation of single hapten-specific B lymphocytes is promoted by T-cell factor(s) distinct from T-cell growth factor.

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Abstract
Hapten-specific B lymphocytes reactive to fluorescein were prepared from mouse spleen, placed singly in 10 .mu.l culture wells and stimulated with fluorescein-polymerized flagellin in the presence of conditioned media (CM) from various concanavalin A-stimulated cloned T-cell tumors or hybridomas. Antigen plus appropriate CM triggered 5-9% of the B cells into both clonal proliferation and differentiation into antibody-forming cells. Antigen alone stimulated 0.5-0.8% of B cells and CM alone stimulated < 0.1%. This bioactivity was termed B cell growth and differentiation factor(s) (BGDF). Four CM rich in T cell growth factor (TCGF), namely, CM from spleen and the lines EL4, T6 and 123, contained BGDF. The lines T19.1 and WEHI-3 lacked BGDF and TCGF. Four lines of evidence suggested that BGDF and TCGF were distinct molecules. The BGDF/TCGF ratios in the various CM varied. On gel filtration TCGF eluted as a sharp peak corresponding to a MW of .apprx. 35,000, BGDF eluted over a range corresponding to a MW of 25,000-60,000. The activity of TCGF in EL4-CM was markedly reduced by treatment with guanidine HCl while BGDF activity was not. BGDF showed more heterogeneity than TCGF on hydrophobic chromatography. All CM or fractions active in promoting B cell division also promoted differentiation to antibody-forming cells. Thus, antigen and a T cell product can synergize to directly activate a single B lymphocyte.