EXPRESSION OF HEMATOPOIETIC-CELL MARKERS BY RETINAL-PIGMENT EPITHELIAL-CELLS

Purpose. We investigated the expression of various isoforms of the hem atopoietic cell marker CD45 on retinal pigment epithelial cells in rel ation to their expression of CD68 and the cytokine-reactive intercellu lar adhesion molecule-1 (ICAM-1). We also determined the effect of the pro-inflammatory cytokines IL-1 beta, TNF alpha and IFN gamma on the expression of these molecules by RPE cells in culture. Methods. Monola yers of RPE cells between 3rd and 7th passages were cultured in the pr esence or absence of cytokines, followed by immunohistochemical staini ng for CD45 (170-220 kD), CD45RA (205 and 220 kD), CD45RO (180 kD), CD 68 and ICAM-1, using the alkaline phosphatase-anti-alkaline phosphatas e (APAAP) technique. Total (membrane and cytoplasmic) expression of ea ch of the three CD45 isoforms was determined by enzyme-linked immunoas says (ELISA). Results. The majority of RPE cells expressed all isoform s of CD45 on their membranes and the pattern of expression of these mo lecules was not modified by culture. The greatest intensity of membran e staining was consistently observed with antibodies to CD45RA (205 220 kD), while CD45 (170-220 kD) showed to be the predominant isoform within he whole cell, as judged by ELISA assays. Unlike the membrane e xpression of CD45, only 20% of RPE cells stained for the macrophage su rface molecule CD68 following 4 h of culture, but progressive increase in the proportion of CD68 positive cells was observed by extending th e culture to 24 and 48 h. Neither the expression of CD68 nor the vario us isoforms of CD45 we:re modified by incubation with pro-inflammatory cytokines. Staining for ICAM-1 was observed in 21-25% of RPE cells th roughout the 48 h culture. However, incubation with 50 pg/ml of IL-I b eta, TNF alpha and IFN gamma caused a marked increase in the RPE cell expression of ICAM-1 following 4, 24 and 48 h culture. Conclusions. Th e observations suggest that hematopoietic cell markers are constitutiv ely expressed on RPE cells and that functions governed by these molecu les are not influenced by pro-inflammatory signals. Expression of hema topoietic molecules by RPE cells may influence the macrophage-like pro perties of these cells and may also aid in the identification of RPE c ells during pathological processes, particularly in the proliferative retinopathies, where these cells undergo phenotypic and functional cha nges.