Immunological analysis of human microglia: lack of monocytic and lymphoid membrane differentiation antigens

While it is certain that reactive microglia (phagocytes in damaged brain tissue) originate from monocytes, the derivation of resting microglia (argentophilic cells in undamaged brain tissue) is not clear. In order to examine a possible lymphocytic and/or monocytic origin for resting microglia, cryostat sections of presumably normal human brain tissue were treated with anti-lymphocyte, anti-monocyte and anti-beta 2-microglobulin sera and then stained with the immunoperoxidase technique. No positive reaction was obtained. It must be concluded that resting microglia are not derived from mononuclear blood cells.