Reactive microglia with membrane features of mononuclear phagocytes.

An inflammatory response was induced by the implantation of cover-slips into the brains of rabbits. The cytomorphology of the glass-adhering cells, their phagocytic properties and their enzymatic activity were characterized and these features were correlated with the presence of membrane markers. Mononuclear cells with foamy cytoplasm, with marked phagocytic potential and strong activity of nonspecific esterases consistently showed IgG- and C-receptor activity. Multinuclear giant cells, which increased in number after prolonged implantation, exhibited comparable features. In contrast, mononuclear cells of fusiform appearance with a low activity of nonspecific esterases and a poor phagocytic potential lacked the IgG-receptor. A close relationship between the mononuclear phagocytic cell and reactive microglia is postulated. The authors conclude that the inflammatory response observed under their test conditions was characterized by the prevalence of phagocytic cells with membrane characteristics of the monocyte-macrophage series.