The expression of α(v) and β₃ integrin subunits in the normal human Fallopian tube epithelium suggests the occurrence of a tubal implantation window

The co-expression of α₁β₁, α₄β₁ and α(v)β₃ integrins in the human endometrium coincides with the implantation window. The α(v)β₃ integrin is expressed in the apical surface of the luminal epithelium and may serve to anchor trophoblast cells in the adhesion phase of implantation. Using immunohistochemistry, we compared the expression of α(v), α₁, α₄ and β₃ integrin subunits in samples of normal human Fallopian tube and endometrium obtained from five women in the non-receptive period (luteal phase days 2-4) and from another five women in the receptive period (luteal phase days 6-8). The staining was quantified visually on a scale of 0 to ++, according to the intensity and density of stained cells. The α(v) subunit is expressed in the Fallopian tube epithelium during both periods in a pericellular distribution. The β₃ subunit is also expressed in the same location, but it is up-regulated during the period of endometrial receptivity. The other subunits are expressed in localizations which are not relevant to trophoblast adhesion and exhibit little or no difference in the level of expression between the non-receptive and receptive periods. Based on these results we postulate that the expression of the β₃ subunit in the human tubal epithelium is under the same systemic controlling signals as in the endometrium and that the normal tubal epithelium may have an implantation window, at about the same time as the endometrium, that affords the opportunity for trophoblast attachment should a 5-7 day embryo be unduly retained in the tube.