T cell apoptosis at the maternal-fetal interface in early human pregnancy, involvement of galectin-1

The human fetus is not rejected by the maternal immune system despite expressing paternal antigens. Natural killer cells, the major lymphocyte population of the human decidua (dNKs), express genes with immunomodulatory potential. These include galectin-1 (gall), a lectin with apoptotic activity on activated CD8(+) T cells, Th1 and Th17 CD4(+) cells. Although many cell types at the maternal-fetal interface also produce gall, its production by dNKs has been used here to study its function in pregnancy. Media conditioned by dNKs containing gall induced apoptosis of activated T cells. This effect was blocked by anti-gall antibodies. Decidual T(dT) cells but not peripheral T (pT) cells bound gall and presented a distinct glycophenotype compatible with sensitivity to gall. Annexin V staining, TUNEL, and hypodiploidy showed a substantial proportion of apoptotic dT cells. Immunohistochemistry revealed widespread expression of gall as well as periglandular apoptotic dT foci that colocalized with dNKs. Thus, secretion of gall by dNKs and other decidual cells contributes to the generation of an immune-privileged environment at the maternal-fetal interface.