HUMAN RETINAL MICROGLIA EXPRESS PHENOTYPIC CHARACTERISTICS IN COMMON WITH DENDRITIC ANTIGEN-PRESENTING CELLS

Neural tissue has been considered to be immunologically privileged and major histocompatibility complex (MHC) class II antigens not expresse d in normal human brain grey matter and retina. In the present study w e compare phenotypic characteristics of human retinal microglia and de ndritic Langerhans cells, including their morphologies and distributio n, MHC class II and CD45 antigen expression and nucleotidase reactivit y. Levels of class II expression were measured using optical densitome try in combination with standard immunohistochemical techniques applie d to retinal flatmounts. The results indicate that ramified retinal mi croglia have features in common with dendritic antigen presenting cell s of cornea and conjunctivum, including the constitutive expression of MHC class II antigens.