Comparative T-cell responses during pregnancy in large animals and humans

PROBLEM: Placentation in different large animal species shows a remarkable diversity in the level of trophoblast invasion into the maternal endometrial tissues. We wish to determine the influence of implantation on T-cell responses during pregnancy. METHOD OF STUDY: Review of the literature and current data. RESULTS: alpha beta -TCR (+) T cells are only prominent during early pregnancy in species with relatively non-invasive placentation (pig and horse) but are rapidly downregulated in species with more invasive placentae. gamma delta -TCR (+) T cells are prominent in species with moderate trophoblast invasion (ruminants) where they increase dramatically during mid and late pregnancy. gamma delta -TCR (+) T cells remain prominent during late gestation in species with highly invasive placentation (humans) and, in addition, a distinct gamma delta T-cell population is present in first trimester decidua where it may play a regulatory role in controlling natural killer cell activity. The gamma delta -TCR (+) population present in both ruminants and humans shows large granular morphology and contains antimicrobial proteins, suggesting their function may be to protect the uterine environment from infection during pregnancy and parturition. CONCLUSION: The comparative analysis of T-cell responses during pregnancy in different large animal species supports an increasing role for cells of the innate immune response (NK and gamma delta T cells) and a downregulation of the adaptive immune response with increasingly invasive placentation.