SUMMARY
Pupose:
To evaluate the pattern of expression of MHC Class II in vitro in human retinal pigment epithelium (RPE) explant cultures treated with interferon-gamma (IFN-γ), and in vivo in rabbit RPE after subretinal injection of IFN-γ.
Methods:
Class II expression was studied on RPE by immunohistochemistry in explant cultures of 6 adult human eyes (all over 70 years), 4 fetal human eyes, and in 12 albino rabbit eyes. The human explants were stimulated with IFN-γ (50 U/ml) for 72 hours prior to immunostaining for Class II. The rabbit eyes were injected in vivo subretinally with 500 U of IFN-γ and analyzed immunohistochemically 3 days later.
Results:
A heterogeneous pattern of Class II expression was present on IFN-γ stimulated RPE in both in vivo and in vitro experiments. In aged human eyes the percent of Class-II positive cells was higher in the periphery than the posterior pole (macular region) (P<0.01), however there was no such difference in the fetal eyes.
Conclusion:
RPE cells are heterogeneous in their expression of HLA Class II after stimulation with IFN-γ in both in vitro and in vivo studies. Regional differences in Class II are seen in aged human eyes but not in fetal human eyes. This study provides evidence of functional heterogeneity of RPE and it is supportive of previous studies demonstrating phenotypic RPE heterogeneity.