Suppression of Lymphocyte Signal Transduction by Murine Mastocytoma Ascites

The lymphocyte signal transduction, as determined by intracellular free Ca²⁺ mobilization of concanavalin A-stimulated T lymphocytes and of anti-immunoglobulin μ chain antibody-stimulated B lymphocytes, was suppressed in spleen cells from mice injected with murine Pl.HTR mastocytoma-induced ascites and in spleen cells treated with the ascites in vitro, The suppression was observed both at the peak level and in the reactive pattern of Ca²⁺ influx. in the suppression, the ascites were replaceable with tumor culture supernatants or tumor homogenates. Correspondingly, primary and secondary cytotoxic T lymphocyte (CTL) responses of DBA/2 mice to allogeneic antigen were also significantly suppressed by injection of the syngeneic Pl.HTR tumor-derived ascites. This new finding suggested that the mechanism of the tumorous ascites or of the tumor-derived factor-mediated immunosuppression involves at least in part the suppression of the early event of the signal transduction for lymphocyte activation.