MODULATION OF MHC CLASS-II EXPRESSION IN THE ABSENCE OF LYMPHOCYTIC INFILTRATES IN ALZHEIMERS RETINAE

This study describes the expression of MHC class II antigens in retina l flat mounts from normal donors and patients with Alzheimer's disease (AD). We confirm previous observations of MHC class II immunoreactivi ty on microglia in normal retinae, while observing insignificant level s of reactivity on endothelial cells (EC). A significantly increased l evel of MHC class II expression was detected in AD retinae. This incre ased immunoreactivity was found to occur in the absence of lymphocytic infiltrates, suggesting that the pathogenesis of AD in the retina may be distinct from that reported to occur in some regions of the brain. MHC class II expression, measured using computerized optical densitom etry, appeared to be increased principally as a result of induced MHC class II immunoreactivity on EC. Ramified microglia and perivascular m acrophages, although hypertrophied, appeared to show unchanged levels of MHC class II expression. These findings are consistent with earlier suggestions that both aberrant MHC class II expression and suppressor activity of resident macrophages may restrict immune responses.