Endometrial microbes and microbiome: Recent insights on the inflammatory and immune "players" of the human endometrium

In recent years, extended scientific works shed light on the important role played by\r\nthe endometrium in early pregnancy. This review examines our current knowledge\r\nabout the delicate balance between microbial and cellular immune agents at endometrial\r\nlevel: All of them might affect endometrial receptivity. In contrast to the classical\r\nthinking of human endometrium as a sterile tissue, several recent studies have\r\ndrawn attention to a resident population of microorganisms, which reaches only a\r\n30% of concordance with those of the cervical‐vaginal flora. At present, the understanding\r\nof the microbiome in relation to human reproduction is in its infancy and\r\nfurther studies are needed to clarify the activity of endometrial microbiome and the\r\npossible effects of a “reproductive tract dysbiosis” on fertility. Moreover, in the\r\nhuman endometrium, there is a complex system works preventing the risk of infection\r\nas well as enabling, when pregnancy occurs, the acceptance of the blastocyst. In\r\nthis way, the endometrium plays a central role in the uterine immune surveillance. A\r\nbetter understanding of the different agents that may affect endometrial receptivity\r\nwould improve the diagnosis and treatment of obstetric complications related to defective\r\nimplantation and placentation.