Immune regulation during pregnancy in relation to allergy and in women undergoing in vitro fertilization

During pregnancy, the fetus expresses both maternal and paternal antigens. To the mother, the paternal antigens are foreign, providing her immune system with an interesting challenge. The fact that the fetus is not normally attacked and rejected implies that mechanisms of tolerance must exist. Pregnancy has long been considered to cause a redirection of the maternal immune responses towards a less aggressive type. Allergic disease has also been associated with that same redirection of immune responses, suggesting that this deviation may be more pronounced in allergic women during pregnancy. Several observations support the concept of a role of the immune system in the etiology of unexplained infertility, associating a redirection of the immune responses towards a more aggressive type with pregnancy loss and pregnancy failure. The aim of this thesis was to investigate the immune responses during pregnancy in allergic and non-allergic women, and in infertile women undergoing IVF treatment. We hypothesized that allergic women would have a more pronounced Th2-deviation than non-allergic women towards paternal antigens during pregnancy and that an unsuccessful outcome of IVF treatment would be associated with aberrations in circulating leukocyte populations and a paternal antigen-specific Th1 and Th17 bias. An increased number of both spontaneous and paternal antigen-induced Th2-like cytokine-secreting cells in peripheral blood was associated with pregnancy in 54 women with pregnancies defined as normal. The allergic pregnant women did not have a more pronounced Th2-deviation than the non-allergic women, as measured by numbers of cytokine-secreting cells. However, when analyzing cytokine levels in cell supernatants, we did observe lower Th1 responses towards paternal antigens in the allergic compared with non-allergic women. Additionally, allergy was associated with a reduced capacity to induce anti-inflammatory IL-10 responses towards paternal antigens. In 25 infertile women undergoing IVF, the peak levels of the majority of paternal antigen-induced cytokines and leukocyte populations investigated coincided with the maximal levels of gonadotropins administered during IVF treatment, suggesting that controlled ovarian hyperstimulation has a general stimulatory effect on the immune system and that it may be regarded as an inflammatory state. During the treatment, no differences were found regarding cytokine responses to paternal antigens in peripheral blood or the numbers or proportions of circulating leukocyte populations between women with a successful or unsuccessful outcome of IVF. We did see higher numbers of Th2-associated cytokine secreting cells and a lower proportion of lymphocytes in the pregnant compared with the non-pregnant women four weeks after embryo transfer, however, in line with previous findings of immune modulation during pregnancy. In conclusion, normal pregnancy seems to be characterized by a less aggressive type of immune responses, possibly more pronounced in allergic women. This may be of importance for the in utero influences on childhood allergy development. An unsuccessful outcome of IVF does not appear to be associated with a more aggressive type of immune responses towards paternal antigens or aberrations in circulating leukocyte populations, although this should be confirmed in a larger study. The results in this thesis also indicate that the hormonal therapy during IVF treatment has a stimulatory effect on the immune system, generating an inflammatory state.