Systemic active suppression is not necessary for successful allopregnancy.

To investigate the role of systemic suppression during allopregnancy, CBA/J female mice were immunised against H-2d prior to mating. Cytotoxic T lymphocyte (CTL) activity was tested at days 14-16 of pregnancy. A reduction of CTL activity was observed only in multiparous animals. Although a nonspecific suppression was detected in isopregnancy, suppression was more marked in allopregnancy. Conversely, the CTL activity observed in the spleen during the first pregnancy (iso or allo) was always significant in mice presensitized with 2 or 3 alloimmunizations prior to pregnancy. Such animals have in vivo effector cells, since allografts of Sarcoma Sa1 were rejected in secondary fashion in alloimmunized mice, while the fetus remained unharmed. These observations demonstrate that allospecific anti-MHC CTLs are specifically impaired in multiple allopregnancy, but also tend to rule out theories postulating that systemic suppression of CTL generation and function is required for successful allopregnancy.