Biochemical characterization of B cell stimulatory factors for lipopolysaccharide-preactivated B cell blasts: distinction from other known lymphokines.

We have performed a biochemical characterization of B cell stimulatory factors (BSF) produced by Con A-stimulated mouse spleen cells that stimulate growth of lipopolysaccharide (LPS)-preactivated B cells (designated BSF-LPS). Two biochemically distinct forms of BSF-LPS were identified in preparative isoelectric focusing, one acidic form having a pI of 3.9-4.4 and a more basic form with a pI 5.2-5.9. The biochemical heterogeneity of the BSF-LPS activity from Con A-stimulated spleen cells was further demonstrated by ion exchange chromatographies using a fast protein liquid chromatography (FPLC) system. The acidic and the basic forms of BSF-LPS could be totally separated from each other and both are distinct from interleukin-2 (IL-2). Moreover, extending the characterization of the BSF-LPS, together with the use of various murine assay systems for BSF, we could formally exclude that IL-4 or IL-5 accounted for the BSF-LPS activities. In summary, our data provide evidence for the existence of heterogeneous BSF-LPS which maintain growth of LPS-preactivated B cell blasts, and show that these factors can be distinguished from the other lymphokines which have been involved in the control of the cell growth of murine B lymphocytes.