Expression of the histocompatibility glycoprotein HLA-DR in neurological disease.

Reactive microglia or macrophages expressing the histocompatibility glycoprotein HLA-DR were detected in many neurological diseases including Alzheimer's, Parkinson's, Pick's and Huntington's diseases, parkinsonism-dementia of Guam, amyotrophic lateral sclerosis, Shy-Drager syndrome, multiple sclerosis and AIDS encephalopathy. Reactive astrocytes, also present in these conditions, were established as a population distinct from the HLA-DR positive microglia by double immunostaining for glial fibrillary acidic protein and HLA-DR. A distinctive pattern of HLA-DR positive cells was seen in each disease entity. Areas known to contain pathology always stained positively, and, in several cases, reactive microglia appeared in areas that would otherwise not have been suspected of being involved in the pathological process. HLA-DR staining, which outlines the surface membranes of positive cells, was so strong that lesioned areas could frequently be identified in sections with the naked eye. In adjacent sections stained with H&E or sections destained of HLA-DR and then restained with H&E, gliosis was often hard to identify except on close microscopic inspection. The results suggest that HLA-DR staining may be a valuable addition to standard neuropathological methods and might be useful in investigating diseases where pathology has not yet been identified.