Menstrual blood contains immune cells with inflammatory and anti-inflammatory properties.

AIM: Successful pregnancy requires balanced regulation of immune cells at the feto-maternal interface. Systemic monitoring of the immune system cannot precisely outline local immune status in the uterus. In this survey, endometrial immune milieu was investigated using a non-invasive method of analysis of menstrual blood (MB). The results were compared with peripheral blood (PB).

METHOD: PB and MB of healthy fertile women (n = 15) were collected simultaneously on the second day of their menstrual cycle. T and natural killer T cell subpopulations were immunophenotyped by flow cytometry.

RESULTS: Among examined cell populations, the frequency of CD4 + Foxp3+, CD4 + Foxp3 + CD25-, CD4 + Foxp3 + CD25+ and IL17+ T cells (P = 0.022, 0.028, 0.017 and 0.005, respectively) and TCRαβ+, CD45RO+, CD16-, IFNγ + and IL17+ NKT (CD56 + CD3+) cells (P = 0.010, 0.037, 0.038, 0.015 and 0.021, respectively) were significantly higher in MB compared with PB. Conversely, PB contained a higher percentage of CD16+ T cells (P = 0.025) in comparison with MB.

CONCLUSION: MB contains cells of an inflammatory and anti-inflammatory nature, implying the existence of finely tuned cell homeostasis during menstruation. Our results imply that MB could be viewed as an easy-to access specimen for monitoring endometrial immune cells, especially those that have preferential endometrial localization.