Active suppression of host-versus-graft reaction in pregnant mice VIII. The uterine decidua-associated suppressor cell is distinct from decidual NK cells

The fetus resulting from allogeneic mating expresses a variety of antigens that may serve as targets for rejection by the maternal immune system. Accumulation of non-T suppressor cells into the uterine decidua of allopregnant mice may serve to prevent such rejection. It has been previously shown that the suppressor activity in decidua during the second half of murine pregnancy is predominantly associated with a population of small lymphocytes with cytoplasmic granules that lack T-cell markers and inhibit the generation of cytotoxic lymphocytes (CTL) against paternal alloantigens both in vitro and in vivo. Since natural killer cells (NK) also possess cytoplasmic granules and may regulate the murine immune response, we examined the hypothesis that the decidua-associated non-T suppressor cell may represent a regulatory type of NK cell. Similar to NK cells, the decidua-associated suppressor cell expressed FcR for IgG. Unlike NK cells, the decidua-associated suppressor cell proved resistant to treatment with anti-asialo GM1 + C'. Sedimentation velocity examination demonstrated that decidua-associated NK activity was associated with cell population with a modal sedimentation of 4 mm/hr that was larger than the decidua-associated suppressor population. Potent suppressor cell activity was also recovered from the decidua of NK deficient allopregnant bg/bg mice. Therefore, decidua-associated NK cells and suppressor cells represent two distinct populations.