[NK cells in the physiology of the fetomaternal relationships]

The NK cells are large granular lymphocytes that are found as approximately 2-15% of the global peripheral lymphocytes. As endometrial granulocytes, they represent 70% of the decidual leukocytes during the first trimester of pregnancy, with a progressive decreasing until term. The complex actions of these numerous and active cells, consist in: 1) placental regulation and control, based on the receptors for the HLA--G and HL--C antigens, that are trophoblast specific and act as universal inhibitors of the NK cells; 2) secretion of a large range of cytokines as IL-1, TNF alpha, IL-8, TGF, IFN gamma, GM-CSF, CSF1 which regulate the trophoblastic proliferation, differentiation and invasion; 3) removal of abnormal trophoblastic cells, which may appear in such a proliferating cell population; 4) infectious protection of the placental unit, due to their unspecific cytotoxic effect. In conclusion, the NK lymphocytes have important implications in the formation of the decidua, as the maternal side of the fetomaternal interface and they are deeply involved in the evolution of normal pregnancy concerning the nutritional, hormonal and immunologic aspects.