Menstrual cycle dependent expression of CD44 in normal human endometrium

CD44 is a cell surface glycoprotein known to be a hyaluronate receptor, which functions in lymphocyte homing and cancer metastasis. We have previously shown that CD44 molecules are expressed in normal endometrial tissue. In this study we immunohistochemically examined expression of CD44 glycoproteins in normal human endometrial tissue to gain insight into roles of CD44 molecules. No expression of the CD44 standard form was observed with 11 endometria in the proliferative phase. On the contrary, 13 of 19 secretory phase endometria were stained intensely by anti-CD44 standard form antibody; all CD44-positive cases were in the mid and late secretory phases. Among the 13 CD44-positive endometria, four also were positive for the CD44 variant with exon v6. CD44 molecules were present at all but the luminal cell surfaces. These results indicate that expression of CD44 depends on menstrual cycle, suggesting that CD44 molecules might be involved in implantation of fertilized ovum in endometrium.