Characterization of hormone-dependent suppressor cells in the uterus of mated and pseudopregnant mice
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The survival of the implanted "fetal allograft" has been attributed to the action of local decidua-associated suppressor cells. These suppressor cells are Fc-receptor positive small lymphocytic cells lacking T-cell markers which arise following implantation, are localized at the implantation site, and block the action of IL-2 that stimulates NK and T effector cells. Kinetic studies have demonstrated the occurrence of an earlier peak of suppressive activity occurring 2-3 days after mating prior to implantation. The cells associated with pre-implantation suppression differs significantly from post-implantation suppressor cells. Velocity sedimentation studies show that early suppression is associated with large cells sedimenting at a modal velocity of 6-7 mm/hr. Suppressive activity from cells of similar size is also present in the uterine lining of hormonally-treated, pseudopregnant mice. In addition, suppressor cells can be demonstrated in the non-pregnant uterus at the time of estrus. These observations suggest suppressor cell activity may be hormonally regulated. The suppressor cell(s) in pseudopregnant mice bears Lyt 2.1 and Thy 1.2 surface antigens and suppressor(s) present in the pregnant animals bears Lyt 2.1 and Lyt 1.1. Although the suppressor cell was large, it did not appear to be a macrophage because it was resistant to antibodies to Mac-1 and FcR cell surface markers but susceptible to anti-T cell reagents. Furthermore, suppression was not mediated by a soluble factor that has been associated with the small lymphocytic suppressor. Thus, the suppressor activity present in the pre-implantation uterine lining appears to differ significantly from the suppressor cell activity found after implantation. The possible role of a hormone-activated suppressor T cell in the success of the pregnancy is discussed.