INTEGRIN MAC-1 AND BETA-AMYLOID IN MICROGLIAL RELEASE OF NITRIC-OXIDE

The beta-amyloid protein associated with Alzheimer's disease (AD) has been well characterized biochemically; however, its primary biological function and mode of action in AD has not been determined. We have sh own previously that beta-amyloid (beta 25-35), in combination with int erferon-gamma (IFN-gamma), can induce nitric oxide release from cultur ed hippocampal microglial cells. In the present study, binding of beta -amyloid with the leukocyte integrin Mac-1, a cell surface receptor on microglia, was studied by observing (1) inhibition of beta-amyloid (b eta 25-35)-mediated release of nitric oxide from cultured microglial c ells following exposure to monoclonal antibodies against Mac-1 (antj-C D18 and anti-CD11b) and (2) competitive binding of fluorochrome-labele d beta 25-35 with anti-CD18 or anti-CD11b using fluorescent flow cytom etry. Wt.3 (anti-CD18 antibody) and OX42 (anti-CD11b antibody) were as effective as opsonized zymosan at inducing the release of nitric oxid e from microglia. Furthermore, Wt.3 and OX42 acted synergistically to induce maximum nitric oxide release. An interaction between beta-amylo id and CD18 of Mac-1 was evidenced by the suppressive action of beta 2 5-35 on Wt.3-mediated release of nitric oxide and the synergistic acti on between OX42 and beta 25-35 in inducing nitric oxide release from m icroglia. The tissue culture study was supported by competitive bindin g assays of fluorochrome-labeled beta 25-35 and Mac-1 antibodies (Wt.3 or OX42). The majority of microglial cells (71%) did bind biotinylate d beta-amyloid in the presence of cytochalasin B, suggesting that beta -amyloid binding to microglia is a receptor-mediated event. Furthermor e, pre-exposure to Wt.3, but not OX42, significantly decreased binding of biotinylated beta 25-35 to microglia. These findings suggest that CD18 of Mac-1 may play a role in beta-amyloid-mediated release of nitr ic oxide. (C) 1997 Elsevier Science B.V.