Immunohistochemical staining of human brain with monoclonal antibodies that identify lymphocytes, monocytes, and the Ia antigen

Using immunoperoxidase histochemistry, human brain sections obtained at biopsy were labeled with monoclonal antibodies which identify human lymphocytes subsets, monocytes, and the Ia antigen. Staining of a population of cells in white matter was present with the anti-Ia and the anti-M1 (monocyte-associated) antibodies but not with any of the 8 monoclonal antibodies which react with human T-cell subsets (anti-T1, 3, 4, 5, 6, 8, 10 and 12). The Ia antigen was present on 1–2% of cells in white matter, and approximately 5% of cells in white matter were M1-positive. Ia-positive cells demonstrated a pattern of diffuse surface membrane staining whereas the M1 antigen appeared to cluster at proximal cell processes. Definitive identification of these cells as microglial cells, astrocytes or oligodendrocytes was not possible. These findings demonstrate that: (1) cells which beam the Ia and M1 determinants can be found in histologically normal human white matter, and (2) human oligodendrocytes do not react with monoclonal antibodies (anti-T5 and anti-T8) that identify human suppressor/cytotoxic cells.