FURTHER-STUDIES ON THE IDENTIFICATION OF THE PHAGOCYTOSIS RECEPTOR OFRAT RETINAL-PIGMENT EPITHELIAL-CELLS

We have previously produced a polyclonal antiserum (R(1)S(5)) against a plasma membrane-enriched fraction of rat retinal pigment epithelial (RPE) cells which inhibits the phagocytosis of photoreceptor outer seg ments (OS) by these cells, This antiserum has now been used to purify a subset of RPE membrane glycoproteins. Using a combination of lectin affinity chromatography, and chromatography on an affinity column made with R(1)S(5)-IgG, we have enriched an RPE membrane extract about 100 -fold. This enriched extract contains only 12 components, all of which are glycoproteins, and retains the ability to adsorb out the inhibito ry activity of antiserum R(1)S(5). This shows that one or more of thes e glycoproteins recognizes an inhibitory IgG in R(1)S(5) and suggests that on- or more of these glycoproteins may participate in the phagocy tosis of OS by RPE cells, possibly as the phagocytosis receptor. We ha ve performed N-terminal microsequencing of seven of these glycoprotein s: four of the seven, with Mrs of 34, 36, 51 and 55 kDa, show no seque nce homology to any known proteins. (C) 1996 Academic Press Limited