LONG-LASTING PERIVASCULAR ACCUMULATION OF MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-II POSITIVE LIPOPHAGES IN THE SPINAL-CORD OF STROKE PATIENTS - POSSIBLE RELEVANCE FOR THE IMMUNE PRIVILEGE OF THE BRAIN

Six cases of middle cerebral artery occlusion are presented in which t he cellular changes accompanying descending degeneration of the latera l corticospinal tract were studied at different time points (5 days-10 years) following the insult. Microglia and perivascular cells were fo und to ingest large amounts of myelin degradation products, while expr essing high levels of major histocompatibility complex (MHC) class II molecules. Activation of perivascular macrophages, as indicated by inc reased class II expression, lasted for many years and appeared to foll ow down-regulation of both phagocytic activity and class II expression on parenchymal microglia. TUNEL labeling was absent from both microgl ia and perivascular cells at all time points investigated. Indirect ev idence is presented that microglia may transfer myelin degradation pro ducts to the perivascular space. Perivascular cells which express MHC class II molecules constitutively do not appear to leave the perivascu lar compartment in large numbers and could release myelin degradation products into the cerebrospinal fluid. The possible immunological cons equences of these findings are discussed with respect to their possibl e relevance for antigen presentation and autoimmune central nervous sy stem disease.