Functional studies on B-cell hybridomas with B-cell surface antigens. III. Differentiative response to phorbol esters.

Phorbol esters have been shown to induce differentiation of human lymphoid cells into the mature stage. Murine lymphocytes, however, have not been found to be induced the terminal differentiation by these products. In this study, TH2.52, a subclone of B-cell hybridomas between M12.4.1 B lymphoma of BALB/c mice and normal B cells of C57BL/6 (B6) mice was treated with 12-O-tetradecanoylphorbol-13-acetate (TPA) and the differentiative effect of TPA was examined. TPA treatment inhibited the spontaneous proliferation of TH2.52 and induced significant IgM secretion by the hybrid. In contrast, M12.4.1 did not develop any IgM secretion when treated with TPA. The differentiative effect of phorbol esters on TH2.52 closely correlated with their tumor-promoting activity. In addition, the differentiative response of TH2.52 to TPA was completely blocked by retinoic acid (RA). Moreover, TH2.52 cells treated with TPA were demonstrated to decrease the expression of Iab, Iad molecules as well as IgM molecules on the cell membrane by analyses of flow microfluorometry (FMF) and quantitative absorption tests. On the other hand, Iad expression of M12.4.1 did not change under the same conditions. The result clearly demonstrates that TH2.52 cells can be induced to differentiate into IgM-secreting cells after treatment with TPA, followed by the decrease in the expression of B-cell surface antigens on the cell membrane.