Immunological aspects of maternal-foetal interactions in mice

Abstract: Mammalian pregnancy is an immunological paradox. The foetus, which expresses both paternal and maternal cell-surface molecules, has to be protected from rejection by the maternal immune system. At the same time, the mother has to have an efficient immune defence and must provide her offspring with antibodies.The first part of this thesis investigates some of the mechanisms involved in the foetal avoidance of maternal rejection reactions. Placental absence of MHC class II expression, as well as a bias for Th2-cytokines at the maternal-foetal interface are suggested to be important for foetal survival. The results showed that placental MHC class II expression cannot be induced in vivo. Transfections of trophoblast cells with MHC class II genes, however, resulted in detectable MHC class II cell-surface expression, indicating that a post-transcriptional block does not exist in these cells.By using IL-4- and IL-10-double deficient mice, it was shown that neither maternal nor foetal expression of these cytokines were crucial for completion of allogeneic pregnancy.In the second part of the thesis, the effect of transmission of immunoglobulin G (IgG) from the mother to the offspring was studied. It was observed that viable maternal Ig-secreting cells occasionally infiltrated the B cell-deficient offspring and remained functional for long periods. In this study "green fluorescent mice" were used as a tool. Furthermore, neonatal ingestion of wild type milk increased the survival of adoptively transferred B-lineage cells in B cell-deficient mice, suggesting that suckling of IgG-containing milk could be used to facilitate B cell-reconstitution in B cell-deficient mice. Finally, results from studies on normal mice showed that absence of maternal IgG-transmission during their neonatal development resulted in elevated serum-IgG production, as well as enhanced immune reactions upon immunisations in adult life. This showed that maternal IgG can have long-term immunoregulatory effects in the offspring.