Immunosubversive role of PGE2 in tumor bearing mice.

: The immunosuppressive activity of tumor cells was studied in vivo and in vitro using C57BL/6 mice and Lewis lung carcinoma (3LL) cells. The SRBC immunization of tumor-bearing mice in vivo gave a lower number of PFC than the control mice. In vitro, employing the Mishell and Dutton technique, the primary immune response of splenocytes from tumor-bearing mice was significantly reduced. The in vitro primary immune response of normal splenocytes was also reduced when the tumor cells or supernatants of tumor cell cultures were present during SRBC immunization. 3LL cells synthesize a large quantity of PGE2 which was also demonstrated in the supernatants of 3LL cell cultures. Nevertheless, as the addition of indomethacin, a potent inhibitor of the prostaglandin synthesis, only partially reduces the tumor cell immunosuppressive action, prostaglandins are conceivably only one of the factors responsible for the immunodepression exerted by the tumor cells.