Active suppression of host-vs-graft reaction in pregnant mice. VII. Spontaneous abortion of allogeneic CBA/J x DBA/2 fetuses in the uterus of CBA/J mice correlates with deficient non-T suppressor cell activity.

The mammalian fetus has been viewed as an unusually successful type of "allograft" and "unexplained" spontaneous abortion as a possible example of maternal rejection. Previous studies have shown the presence of small lymphocytic suppressor cells in the murine decidua which block the generation and reactivation of anti-paternal cytotoxic T lymphocytes (CTL) and lymphokine-activated killer cells (LAK) by elaborating a factor that inhibits the response to interleukin 2 (IL 2). A deficiency of these suppressor cells was associated with implants of xenogeneic Mus caroli embryos in the Mus musculus uterus which are infiltrated by maternal lymphoid cells and aborted. We have also shown a deficiency of such suppressor cells in the lymph nodes draining the uterus of CBA/J females in the process of aborting their semi-allogeneic CBA X DBA/2 F1 progeny. CBA/J females possess significantly lower levels of decidua-associated non-T suppressor cells on day 8.5 to 10.5 of allopregnancy than do mothers that will produce large litters of live babies. The F1 embryos are infiltrated by maternal lymphocytes prior to abortion, and the infiltration and abortion rate appears to be augmented by pre-immunization with paternal DBA/2 spleen cells. Susceptibility to spontaneous abortion is dependent upon maternal age and strain of male mate, and the high abortion rate of CBA/J mated to DBA/2 males can be reduced by immunization with BALB/c spleen cells. The CBA/J x DBA/2J mating combination provides a model of spontaneous abortion in which immunologic factors play an important role and demonstrates that the association between deficiency of decidua-associated suppressor cells and xenopregnancy failure also holds true for the failure of allopregnancies resulting from natural within-species mating.