Studies of the rosette inhibition test in pregnant mice: evidence of immunosuppression?

The rosette inhibition test has been utilized as a measure of immunosuppression following organ transplantation, and we have recently demonstrated that it can also be used in detecting a state of depression of lymphocyte reactivity occurring in pregnant mice. If the depression of lymphocyte reactivity provides an indication of immunosuppression, then this study has shown that, in the mouse, the spleen lymphocytes are immunosuppressed as early as 4 h after fertilization. This state persists for 13–15 days, with a return to normal 4–6 days before full term. A similar depression of normal spleen lymphocytes can be induced in vitro by incubating these lymphocytes with serum taken from pregnant mice 6 and 24 h after mating. The serum factor detected was shown to be stable when heated at 56 °C but not at 72 °C, and to be non-dialysable. It was detected in serum to a dilution of 1 in 64. Further work is being undertaken to investigate this phenomenon and to pursue the purification and identification of the pregnancy factor.