Identification and partial purification of a B cell growth-promoting material utilizing the BCL1 cell line

A B cell growth-promoting factor (BCGF) can be detected in the culture supernatants of activated murine and human spleen cells, human peripheral blood lymphocytes, and a murine thymoma cell line by the use of the B cell leukemic cell line BCL1, which is induced to proliferate in response to this factor. Although this BCGF stimulates BCL1 cells to proliferate, it is not mitogenic for resting B cells but synergizes with dextran sulphate to induce proliferation of the latter cells. This factor has no T cell-replacing activity in an antibody response. BCGF co-purifies with interleukin 2 (IL 2) by gel chromatography and isoelectric focusing but can be separated by phenyl-Sepharose chromatography.