Characterization of human B cell growth factor (BCGF) from cloned T cells or mitogen-stimulated T cells

Abstract

An assay system for the measurement of human BCGF was established by employing anti-id-stimulated B-CLL cells, anti-mu-stimulated normal B cells, or a transformed B cell line. PHA-Sup from PHA-stimulated T cells induced proliferation of anti-lg-stimulated B cells or augmented proliferation of a B cell line, and the activity was dose-dependent. BCGF, IL 2, and BCDF activities in PHA-Sup were eluted in a 17K fraction by gel filtration in 0.5 M NaCl. BCDF activity (pl 5.8) was isolated by chromatofocusing, but BCGF and IL 2 activities (pl 6.5 and 6.9) were not separated. Absorption with an IL 2-dependent T cell line or anti-id-stimulated B-CLL cells showed BCGF and IL 2 were distinct molecules. An IL 2-dependent helper T cell clone, d4, secreted BCGF with the m.w. of 50K. The 50K-BCGF fraction had no IL 2 activity and was eluted in a 19K fraction by gel filtration in 4 M urea and 1 M NaCl. PMA stimulation of normal T cells induced 50K-BCGF, the m.w. of which was reduced to 19K in 4 M urea and 1 M NaCl. 50K-BCGF from d4 cells and 17K-BCGF from PHA-Sup showed a synergistic effect on the proliferation of anti-lg-stimulated B cells. The results show the existence of two distinct kinds of BCGF and the presence of the synergism between them.