RELEASE OF IMMUNOSUPPRESSIVE FACTOR(S) BY MOPC-315 MURINE PLASMACYTOMA CELLS - A POSSIBLE MECHANISM OF DEFENSE

Supernatants were collected from suspensions of MOPC-315 tumor cells h arvested from ascitic tumors and kept for 24 hours in culture medium a nd from cultures of an MOPC-315 tumor-cell kept for a long period of t ime in vitro. The MOPC-315 supernatants were tested for immunosuppress ion of mitogenic stimulation of BALB/c spleen cells by ConA or LPS, of allogeneic response of effector BALB/c spleen cells against target C5 7BL spleen cells, of generation of antibody response against SRBC and of induction of LAK activity. The immunosuppression was marked in all the test systems, was not related to secretion of either C-type partic les or of anti-TNP antibodies and was also induced by MOPC-315 tumor c ells kept in serum-free medium. It is suggested that release of immuno suppressive factor(s) by MOPC-315 tumor cells might play a role in the mechanism(s) of defence of the tumor against the host.