Tumor-mediated immunosuppression: prevention by inhibitors of prostaglandin synthesis.

The addition of MC16 tumor cells (a prostaglandin E2-producing cell line induced in C57BL/6J mice by methylcholanthrene) to cultures of cells to sheep red blood cells. This inhibition can be blocked by adding to the cultures prostaglandin synthetase inhibitors, such as indomethacin, flufenamic acid and aspirin. These MC16 tumor cells are also immunosuppressive in vivo. Mice bearing the syngeneic MC16 tumor become unresponsive to sheep red blood cells as the tumor grows. As in the in vitro test system, inhibitors of prostaglandin synthetases seem to block the immunosuppressive activity of MC16 cells in vivo since tumor-bearing mice, treated therapeutically with indomethacin, responded normally in their production of antibody to sheep red blood cells.