Microglial cells in human brain have phenotypic characteristics related to possible function as dendritic antigen presenting cells

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Abstract
The resting human microglia have previously been shown to be cells of dendritic morphology expressing class II MHC antigens and macrophage specific antigens by immunocytochemical techniques. To examine the relationship between the microglia and the family of dendritic antigen presenting cells (APC), normal white matter from eight normal adults with no neurological disease at autopsy was examined by immunocytochemical techniques to localize antibodies to leukocyte common antigen (LCA), HLA‐DR, CDI (T6), CD4 (T4), and glial fibrillary acidic protein. In addition, enzyme histochemical staining for ATPase, non‐specific esterase (NSE), and acid phosphatase (ACP) was performed. The normal microglia are ATPase + ve, NSE −ve, ACP‐ve, HLA‐DR + ve, LCA + ve, CD1 (T6) + ve and weakly CD4 (T4) + ve. This specialized phenotype closely resembles that of Langerhans cells and suggests that microglia are not simply quiescent phagocytes, but may have a primary role as microenvironmentally specialized APC. The finding of weak anti‐CD4 (T4) immunoreactivity supports suggestions for a central role for this cell in infection of the central nervous system by human immunodeficiency virus type 1.