Immunosuppresive effect of alpha-fetoprotein at different stages of pregnancy in mice

A possible immunoregulatory role of alpha-fetoprotein (AFP), both as contained in amniotic fluid and in isolated form, was investigated at different stages of pregnancy. Virgin, as well as pregnant mice on days 6, 9, 12 or 16 of gestation were immunized by a single intraperitoneal injection of sheep red blood cells (SRBC). Antibody responsiveness in these animals treated with mouse amniotic fluid (MAF) or isolated AFP, was assessed by measuring YM splenic plaque-forming cells (PFC) 4 days after primary immunization. There was a significant suppression of plaque-forming activity in MAF and AFP treated non-pregnant mice. Similar suppression was evident also in animals in which SRBC were injected on days 6 or 9 of pregnancy followed by treatment with MAF or AFP. Conversely, the same treatment did not result in suppression of antibody response to SRBC, injected on days 13 or 16 of gestation. One of the possible explanations of such lack of AFP effect could be increasing production of endogenous AFP which itself already restrained the mother's immune reactivity. The decreased number of PFC in the last week of gestation in non-treated mice may support this assumption.