ALPHA-2-MACROGLOBULIN EXPRESSION IN NEURITIC-TYPE PLAQUES IN PATIENTSWITH ALZHEIMERS-DISEASE

Because it has been suggested that alpha2M could be involved in the ge neration of amyloid peptide, attention was given to a possible associa tion of alpha2M expression and amyloid accumulation in the brain. Ther efore, we investigated the presence of the proteinase inhibitor alpha2 -macroglobulin (alpha2M) in the cerebra of 4 patients with Alzheimer's Disease (AD). One case of a patient with Down's syndrome, 2 cases of patients with Dementia of the Lewy Body type (DLB), 1 case of an aged, clinically nondemented person who displayed many amyloid plaques, and 3 normal aged control brains were also studied. The results obtained by immunocytochemistry with monoclonal antibodies directed against two different epitopes of human alpha2M showed an association of alpha2M. only with neuritic-type plaques in patients with AD. No alpha2M immun oreactivity was found in either preamyloid-type plaques or burned out- type plaques in AD, DLB, or aged nondemented controls. The results do not support a direct role of this proteinase inhibitor in the formatio n of amyloid. Because alpha2M is observed to be associated with reacti ve microglia in the outer border of the neuritic plaques, the data sug gest that alpha2M could be a marker for an inflammatory cellular proce ss in these neuritic plaques.