ONTOGENY AND CELLULAR EXPRESSION OF MHC AND LEUKOCYTE ANTIGENS IN HUMAN RETINA

We have investigated the ontogeny of MHC class I, class II, CD45, and macrophage antigens in wholemounts of normal human fetal retina at 10- 25 weeks gestation (WG) using monoclonal antibodies and immunogold his tochemistry. MHC class I antigens were expressed on retinal vascular e ndothelial cells and provided a useful marker of vessel organization f rom 14-25 WG. Microglial cells expressed immunoreactivity to MHC class I, class II, and CD45 antigens from 10 WG (pre-vascularization) and m acrophage S22 (Mac S22) antigen from 14 WG (post-vascularization), alt hough none of the antigens tested were detected on neuronal or macrogl ial elements. Microglia expressing MHC, CD45, and macrophage antigens occurred in both ramified and rounded forms with no close correlation being observed between morphology and antigenicity. The numbers of imm unoreactive cells labeled with each of the four markers increased stea dily throughout gestation in all specimens studied. Equivalent numbers of microglia expressed MHC class I, class II, and CD45 antigens in re tinae at similar gestational ages; however, our data indicate that mic roglia expressing Mac S22 antigen comprise approximately 40% or less o f the population of MHC and CD45-immunoreactive cells during developme nt. Topographical analyses suggest that MHC class I, class II, and CD4 5-positive microglia enter the retina from both the peripheral retinal margin and the optic disc from at least 10 WG; Mac S22-positive cells appear in association with the development of the retinal vasculature and enter the retina via the optic disc after 14 WG. (C) 1995 Wiley-L iss, Inc.