Presence of T-cytotoxic suppressor and leucocyte common antigen positive cells in Alzheimer's disease brain tissue.

Cells expressing leucocyte common antigen (LCA) as well as T-cytotoxic-suppressor (T8) and T-helper-inducer (T4) antigens were detected in significant numbers in the hippocampus and temporal cortex of Alzheimer but not normal brain tissue. Leucocytes and reactive microglia strongly expressed LCA, as well as the class II major histocompatibility complex (MCH) glycoprotein HLA-DR, but astrocytes stained negatively. Such staining indicates the immunocompetent status of microglia, as well as their phenotypic linkage to blood borne mesodermal lines. T8 and T4 positive lymphocytes were detected in capillaries and the surrounding matrix in smaller numbers than LCA positive cells. The MHC class I (HLA-A,B,C) antigens were detected on capillaries in both Alzheimer and control tissue. The significance of LCA, T4 and T8 cells in Alzheimer's disease is unknown but may be indicative of a cell mediated immune response in the disease.