Functional modifications of the CD4+ and the CD8+ subset due to maternal serum

Numerous experiments have been performed to try to explain the successful gestation of the semiallogeneic mammalian fetus in the immuno-competent mother. A popular hypothesis is that localized intra uterine suppression mediates the immune response and contributes directly to the survival of the fetus. Suppressive factors synthesized at the fetomaternal interface may be transported by the bloodstream and be found in the retroplacental and peripheral blood circulation. In this report we aim to study these modulating factors by exposing a proteinaceous antigen (Candidine or human mono nuclear cells) to unrelated human lymphocytes in the presence of a pool of maternal serum, retroplacental (MAT SR) or peripheral (MAT SP), or to a pool of male or calf serum (MALS or CS). A significant downregulation of the candidine mediated lymphocytic stimulation was observed in the case of the maternal serum. In order to further characterize this inhibition, a quantitative evaluation of the expression of the CD4 and CD8 positive subpopulations was performed. A selective inhibition of the CD4 positive subset was observed. In the PHA stimulation assay in the presence of maternal serum there was an inhibition of the thymidine uptake of unrelated lymphocytes. When studying the different subsets which were stimulated in the presence of maternal serum and control media it was shown that the CD4 positive subpopulation remained unchanged while there was a slight inhibition of the CD8 positive subset in the first case (maternal serum treated). The same CD4 positive inhibitive property of maternal serum was observed when a neoplastic cell line (HUT cells) was used as target for candidine in a stimulation test. This CD4 inhibited expression remained constant as long as the maternal serum was renewed. Maternal lymphocytes however remained resistant to the inhibitive action of maternal serum and did not show any change in their CD4 and CD8 positive subpopulation. By investigating the different blood components, it was shown that the suppressive factor was included in the IgG fraction and synthesized at the placental level. Appearing quite early during the gestation (at the 5-6th week), this factor was vanishing 2 weeks after the delivery.