Objective: To study the lymphocytes, perforin protein and mRNA expression in endometrium of different phases in the menstrual cycle and to explore the regularity and role of the lymphocytes and perforin in the reproductive system.
Methods: Immunohistochemical and in situ hybridization techniques were employed to demonstrate the population, phenotype and mediator (perforin) of lymphocytes in the proliferative and secretory endometrium.
Results: In different phases of the endometrium, there were very few CD3+ typical T lymphocytes, CD4+ helper lymphocytes and CD8+ suppressor/cytotoxic T lymphocytes, while CD56+ lymphocyte (also named NK-like cell) were abundant. CD56+ lymphocytes were absent in postmenopausal endometrium. A double immunohistochemical labelling method demonstrated the co-expression of perforin protein and CD56 antigen of cells in different phases of the endometrium. Quantitative analysis of CD56+ lymphocytes and perforin-positive cells increased in number from the proliferative to the secretory endometrium (P < 0.05). In situ hybridization analysis showed that perforin mRNA positive cells formed islands in proliferative endometrial stroma, but were scattered in secretory endometrium. There was difference between perforin gene expression and protein expression in the proliferative endometrium.
Conclusions: Lymphocytes and perforin expression in the endometrium at different phases of the menstrual cycle are specific and may play an important role in the reproductive system. They may exert a positive influence on embryo implantation and be involved in endometrial stroma breakdown during menstruation.