Functional studies on B cell hybridomas with B cell surface antigens. IV. Direct effects of cytochalasin B on...

We previously established B cell hybridomas between M12.4.1 B lymphoma of BALB/c mice and normal B cell of C57BL/6 (B6) mice. These hybridomas express Iab, Iad, and IgM molecules on the cell membrane, and can induce the generation of IgM secretion when treated with purified goat anti-mouse-mu antibody (anti-mu) without T cell factors. In this study, TH2.54, a subclone of a B cell hybridoma, was treated with cytochalasin B (CB), a fungal product that disrupts microfilaments, and the direct effect of CB on the proliferation and differentiation of TH2.54 was examined. CB considerably suppressed the spontaneous proliferation of hybrid cells. This product, however, did not inhibit the generation of IgM secretion by TH2.54 treated with anti-mu. Surprisingly, CB could directly induce the development of IgM-secreting cells by TH2.54 at a relatively high frequency. Among cytochalasins, dihydrocytochalasin B (H2CB), cytochalasin C (CC), and cytochalasin D (CD) showed marked effects on the induction of IgM secretion as well as CB. In addition, the differentiative effect of CB was greatly inhibited by N6, O2-dibutyryladenosine 3':5'-cyclic monophosphate (dbc-AMP), but not by N2, O2-dibutyrylguanosine 3':5'-cyclic monophosphate (dbc-GMP). Analysis by flow microfluorometry (FMF), cytotoxicity assays, and quantitative absorption tests demonstrated that CB treatment of TH2.54 resulted in a significant decrease in the expression of Iab, Iad, and IgM molecules on the cell membrane. In contrast, parental M12.4.1 neither generated any IgM secretion nor changed Iad expression on the cell membrane under the same conditions. The present study suggests very strongly that microfilament-microtubule systems are not involved in the differentiative process of TH2.54 induced by anti-mu. The results also indicate that CB can provide the initiative signal for differentiation of TH2.54 into the maturation lineage; this is followed by a significant change in the expression of Ia and IgM molecules on the cell membrane.