NK Cells and Fertility Immunological Aspects Review

Abstract

The basic functions of NK cells circulating in peripheral blood and present in immune organs are production of proinflammatory cytokines and cytotoxicity against transformed cells after viral infection, during neoplastic process. Tissue resident NK cells (liver, lungs, lymph nodes, uterus) are phenotypically and functionally distinct in relation to the tissue. Uterus NK cells (uNK) are involved in endometrial transformation during the embryo implantation and progressing pregnancy. There are divided into subpopulations – endometrial NK (eNK) and decidual NK (dNK1, dNK2, dNK3) and memory NK cells after pregnancies (PMdNK). The study of NK cells showed different combination of phenotype markers and relation to function – shifted for cytokines production or for the cytotoxicity. The interesting type of receptors important for uNK function are killer-immunoglobulin-like receptors (KIR) with inhibitory or activating properties. The inhibitory profile KIR receptors (KIR AA) are believed to be unfavourable marker for the embryo implantation and pregnancy as activation of uNK is needed for proper decidual vascularisation (remodelling of spiral arteries), the embryo implantation, induction and regulation of local maternal-foetal tolerance. The disorders of NK number and function are associated with pregnancy complication like recurrent implantation failure (RIF) or recurrent pregnancy loss (RPL). The diagnostic and therapeutic approaches in women with RIF or RPL are including the NK cells characteristics and activity.