Effector Activity of Decidual CD8+ T Lymphocytes in Early Human Pregnancy1

The fetal allograft revisited: does the study of an ancient invertebrate species shed light on the role of natural killer cells at the maternal-fetal interface?

Human pregnancy poses a fundamental immunological problem because the placenta and fetus are genetically different from the host mother. Classical transplantation theory has not provided a plausible solution to this problem. Study of naturally occurring allogeneic chimeras in the colonial marine invertebrate, Botryllus schlosseri, has yielded fresh insight into the primitive development of allorecognition, especially regarding the role of natural killer (NK) cells. Uterine NK cells have a unique phenotype that appears to parallel aspects of the NK-like cells in the allorecognition system of B. schlosseri. Most notably, both cell types recognize and reject "missing self" and both are involved in the generation of a common vascular system between two individuals. Chimeric combination in B. schlosseri results in vascular fusion between two individual colonies; uterine NK cells appear essential to the establishment of adequate maternal-fetal circulation. Since human uterine NK cells appear to de-emphasize primary immunological function, it is proposed that they may share the same evolutionary roots as the B. schlosseri allorecognition system rather than a primary origin in immunity.

Expression and function of PDCD1 at the human maternal-fetal interface

The failure to reject the semiallogenic fetus by maternal T lymphocytes suggests that potent mechanisms regulate these cells. PDCD1 is a CD28 family receptor expressed by T cells, and its ligand CD274 is strongly expressed by trophoblast cells of the human placenta. In this study, we examined whether human maternal T cells express PDCD1. Immunofluorescence examination of uterine tissues revealed PDCD1 expression on CD3+ cells was low in nonpregnant endometrium but increased in first-trimester decidua and remained elevated in term decidua (P < 0.05). In addition, higher relative proportions of term decidual CD8 bright, CD4+, and regulatory T cells expressed PDCD1 in comparison to autologous peripheral blood (P < 0.05). Term decidual T cells also expressed full-length and soluble PDCD1 mRNA isoforms more abundantly than their peripheral blood counterparts (P <or= 0.05). We also examined the effects of PDCD1:CD274 interactions in decidual T cells. Jar choriocarcinoma cells were transfected with CD274 and cocultured with activated decidual CD4+ or CD8 bright T cells for 72 h followed by analysis of cytokine concentration and decidual T cell apoptosis. Compared with empty vector-transfected cells, CD274-transfected Jar cells caused a significant suppression of interferon gamma and tumor necrosis factor alpha production by CD4+ (P < 0.05) but not CD8 bright T cells, while having no effect on secretion of IL10 or T cell apoptosis. These results suggest that the PDCD1:CD274 pathway functions in modification of maternal decidual lymphocyte cytokine secretion during pregnancy.