Beyond Uterine Natural Killer Cell Numbers in Unexplained Recurrent Pregnancy Loss: Combined Analysis of CD45, CD56, CD16, CD57, and CD138

Changes in the number and cytotoxic potential of uterine Natural Killer (uNK) cells have been associated with reduced fertility. To provide a better characterization of immunophenotypes in the endometrium of women with uRPL (unexplained recurrent pregnancy loss), we examined the applicability of a set of five immune cell markers. The concentration (cells/mm(2)) of CD45(+) leukocytes, CD56(+) uNK cells, and CD138(+) plasma cells as well as of CD16(+) and CD57(+) cells, which indicate high cytotoxic uNK cells, were assessed by immunohistochemistry in endometrial biopsies from 61 uRPL patients and 10 controls. Control fertile endometria presented 90–300 CD56(+) uNK cells/mm(2). uRPL cases were classified in subgroups of low (uRPL-CD56(low) < 90 cells/mm(2)), normal (uRPL-CD56(normal) 90–300 cells/mm(2)), and high uNK cell counts (uRPL-CD56(high) > 300 cells/mm(2)). Some cases from the uRPL-CD56(low) and uRPL-CD56(normal) subgroups showed elevated proportions of cytotoxic CD16(+) and CD57(+) cells in relation to CD56(+) cells. In the uRPL-CD56(high) subgroup, the CD57/CD56 ratio was reduced in most samples and the CD16/CD56 ratio was unaltered. Analysis of CD138 excluded the influence of chronic endometritis on these observations. Our results reinforce a link between uRPL and a dysfunctional endometrial environment associated with distinct immune cell profiles.