PROBLEM: Recent evidence emphasizes the role of natural killer cells (NKs) as potential effectors of peritoneal immune surveillance directed against the outgrowth of endometrial cells, refluxed with menstrual debris, in ectopic sites. This NK-mediated cytotoxicity toward autologous endometrial antigens seems to be significantly decreased in endometriosis patients.
METHOD: We set up experiments to clarify which molecules are involved in NK-endome-trial cell interaction. In particular, we evaluated the surface expression and functional activity of intercellular adhesion molecule-1 (ICAM-1), a cell surface glycoprotein that has been identified as one of the ligands for lymphocyte function-associated antigen-1 (LFA-1), present on almost all leucocyte cell types. Immunofluorescence flow cytometry was used to assess ICAM-1 expression on resting and IL 1β-activated endometrial stromal cells in culture. Dermal fibroblasts were used as control cells. Cytotoxicity and binding assays by 51Cr release in presence and absence of a specific monoclonal antibody (mAb) against ICAM-1 were then performed in order to determine the effect of this molecule on NK-mediated cytotoxic and binding activity toward endometrial stromal cells.
RESULTS: The results of this study indicated that ICAM-1 expression on endometrial stromal cells seems to be constitutively higher than on dermal fibroblasts and can be up-regulated upon exposure to IL 1β. Furthermore, a mAb against ICAM-1 strongly inhibits the binding but not the cytotoxicity of NKs toward endometrial cells. No difference in the expression of this molecule was observed throughout the cycle.
CONCLUSIONS: The presence of ICAM-1 on human endometrium might relate to the action of the immunocompetent cells in human specific reproductive events.