Monoclonal SBF produced by a hybridoma: in-vitro and in-vivo suppression of B tumour-cell proliferation.

A suppressive B-cell factor (SBF)-producing hybridoma termed TS-4.44 was established by fusion of B cells which possessed receptors for the Fc portion of IgG (FcR gamma + B cells) and thymidine kinase defective fibroblasts, 3T3-4E cells. The biological properties of hybridoma-produced SBF (Hyb-SBF) are almost the same as those of conventionally prepared SBF (Conv-SBF). Hyb-SBF suppresses (i) plaque-forming cell (PFC) responses in an antigen non-specific manner, (ii) DNA synthesis of lipopolysaccharide (LPS)-activated B cells, but neither concanavalin A (Con A) nor phytohaemagglutinin (PHA)-induced activation of T cells, and (iii) the proliferation of B, but not non-B tumour cells. Once absorbed with L-1210 cells, Hyb-SBF failed to inhibit both PFC and LPS responses. It is important is that Hyb-SBF suppresses the proliferation of L-1210 cells not only in vitro, but also in vivo. The physicochemical properties of Hyb-SBF such as sensitivity to trypsin, pronase and neuraminidase and its molecular weight (43,000), as judged by gel filtration and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) are in accord with those of Conv-SBF. Moreover, it is eluted from a DEAE cellulose column with 0.1-0.3 M phosphate buffer. Thus, monoclonal SBF is thought to be identical with Conv-SBF and could provide us with sufficient material for the analysis of FcR-dependent immunoregulation including surveillance mechanisms controlling the proliferation of B tumour cells.