Modification of thymocytes subsets during pregnancy analysed by flow microfluorometry: role of the alloantigenic status of the conceptus.

Modifications of thymus subsets during pregnancy were monitored using flow microfluorometry and fluorescein-labelled lectins or antibodies. Essentially, it was found that the percentage of peanut lectin-negative (PNA-) cells increased significantly during pregnancy. More interestingly, in the strains tested, the percentage of PNA- cells was more increased in allogeneic than syngeneic pregnancy. This PNA- increase could be mimicked by extracts from syngeneic placenta, but the largest increase in PNA- cells was always observed by injection of allogeneic placental extract, or syngeneic placental extract plus allogeneic cells. These findings suggest that the alloantigenic status of the conceptus does play a role in induction/maintenance of thymus involution, suggesting that it is not a mere hormonal phenomenon and that it could play a role in the events leading to the acceptance of the allogeneic conceptus by the maternal immune system.