Expression of immune system-associated antigens by cells of the human central nervous system: relationship to the pathology of Alzheimer's disease.

HLA-DR is a class II major histocompatibility complex antigen which in the periphery confers antigen presenting capability. We have previously shown that this marker is profusely expressed in cortex of elderly and Alzheimer's disease (AD) patients, as is the receptor for the lymphokine interleukin-2. We now report presence of additional immune-related antigens in AD, and distributional differences from normal elderly controls. In gray matter, HLA-DR immunoreactivity is normally sparse, except in AD where it co-localizes with virtually all neuritic plaques. HLA-DR positive T cells can be demonstrated in Alzheimer's disease brain tissue, as can instances of apposition between putative brain microglia and T cells. In addition, cells with the morphologic characteristics of astrocytes label for natural killer cell antigen (Leu-11), and apparent lymphocytes bearing T helper and T cytotoxic/suppressor cell antigens are observed. These and other data suggest that the glial proliferation and scavenger activity characteristic of Alzheimer's disease may occur in an immune context and may play an important role in the pathogenesis of the disorder.