Isolation and characterization of B cell differentiation factor (BCDF) secreted from a human B lymphoblastoid cell line.

A subclone of a human B lymphoblastoid cell line, CESS-2, spontaneously secreted a kind of BCDF (B-BCDF) in their culture supernatant without any stimulation. B-BCDF induced IgG and IgM secretions in human B lymphoblastoid cell lines, CESS cells and CL-4 cells, respectively. BCDF-responsive CESS cells expressed IgG on their surface, whereas CESS-2, which were able to secrete B-BCDF, did not express surface IgG. B-BCDF could induce Ig-secretion in SAC-stimulated low density peripheral B cells, but did not induce Ig secretion in nonstimulated B cells. B-BCDF did not show any IL 2, BCGF, or gamma-interferon activities. B-BCDF was highly purified by gel filtration on an AcA-34 column, by chromatofocusing and ion exchange chromatography on an HPLC system, and by gel filtration on an HPLC column. Highly purified preparations showed a single protein band in SDS-PAGE analysis. The m.w. and isoelectric points of the factor were 20,000 and pH 5.1 to 5.2, respectively. The minimum protein amount required for Ig induction in B cell lines was 16 ng/ml.