Effect of pregnancy on stimulation of alphavirus immunity in mice.

The state of pregnancy was associated with a marked enhancement of both proliferative and cytotoxic T cell antiviral immune responses after infection of mice with avirulent Semliki Forest virus. Strong responses were obtained from the spleen and the para-aortic lymph nodes that drain the uterus. This immune enhancement seemed to be in response to the increased antigenic challenge that originated from infected placental and fetal tissue and was released during the process of abortion. Immune enhancement was not observed in pregnant mice similarly infected with Ross River virus, which also established an intrauterine infection but does not cause abortion.