Fig. 9.

CD81 overexpression promotes POS binding only in the presence of αvβ5 integrin. Primary RPE isolated from β5^+/+ mice, β5^−/− mice, and RCS rats were transfected with CD81 expression plasmid or empty vector as control. 48 hours after transfection, we evaluated protein expression (A,B) and phagocytic activity (C) of transfectants were examined. (A) Total cell lysates, of equal numbers of cells, were analyzed by western blotting for proteins as indicated. (B) Quantification of western blots shows that CD81 plasmid transfection specifically increased CD81 protein to 1.4–1.6 fold of control cells. Bars show relative CD81 levels in β5^+/+ (black), β5^−/−(dark gray), and RCS RPE (light gray) (mean ± s.d., n=3). (C) Quantification of surface-bound POS following 1 hour of FITC-POS challenge shows that CD81 overexpression increased POS binding by β5^+/+ and RCS RPE, but had no effect on β5^−/− RPE. Bars represent mean ± s.d., n=3, percentage POS bound by CD81 overexpressing RPE cells compared to control transfected cells of the same genotype. POS binding by CD81 transfected β5^+/+ and RCS RPE was significantly increased compared to respective control uptake (P<0.05, Student’s t-test). Remarkably, CD81 transfected β5^−/− RPE did not differ in POS binding from control β5^−/− cells (P>0.5).