Identification of Fc gamma RI, II and III on normal human brain ramified microglia and on microglia in senile plaques in Alzheimer's disease.

Using monoclonal antibodies to the three known human leukocyte IgG receptors, Fc gamma R, we examined the expression of Fc gamma R in normal brains and in Alzheimer's disease. We found Fc gamma RI, II and III immunoreactivity in senile plaques and on ramified microglia throughout the cortex and white matter of normal and Alzheimer's disease brains. Fc gamma RI expression was independently confirmed by a murine isotype binding study. These findings suggest that intrinsic Fc gamma R may play an important role in normal and disordered immune-related processes in the brain. They support the idea that microglia are brain macrophages.