Chemokine and cyclooxygenase-2 expression in human endometrium coincides with leukocyte accumulation

The endometrium contains a resident population of leukocytes, the number and subtype of which vary throughout the menstrual cycle and in early pregnancy. Factors controlling these fluctuations are unknown, but a combination of proliferation in situ and migration from the vasculature has been proposed. Locally acting inflammatory mediators, including specific chemokines and prostaglandins, have been implicated in these processes. Interleukin-8 (IL-8) and monocyte chemoattractant protein-1 (MCP-1) are potent chemoattractants and activators for neutrophils and monocytes respectively. Locally acting prostaglandins modulate vascular permeability, and a synergistic action of prostaglandin E (PGE) with IL-8 has been described. In the present study IL-8, MCP-1 and cyclooxygenase-2 (COX-2), the inducible isoform of prostaglandin synthase, were all localized in the endometrium by immunohistochemistry throughout the menstrual cycle and in early pregnancy. All three inflammatory mediators were localized to the perivascular cells of blood vessels in endometrium and decidua, and additional immunoreactivity for COX-2 was identified in the glandular epithelium. The intensity of immunostaining was reduced in the periovulatory, early and mid-secretory phases and significantly increased premenstrually. These results further support the hypothesis that there is a premenstrual migration of leukocytes into the endometrium mediated by chemokines.