Microgliosis and Impaired Cognition

There is growing evidence that immune responses within the CNS help to determine the course and severity of neurological diseases (1). Microglia, mononuclear phagocytes endogenous to the CNS, are the principal immune cells of the brain. Although normally found in a quiescent state, microglia are activated by a variety of disease-associated signals to release cytokines and cytotoxins. These factors, in turn, promote wound healing or, alternatively, induce neuron injury. Groups of reactive microglia are found scattered throughout the brain following infection by human immunodeficiency virus-1 (HIV-1) or clustered about senile plaques found in Alzheimer’s disease (AD) (Fig. 1; refs. 2 and 3). We propose that chronic reactive microgliosis destroys neurons and contributes to loss of cognitive function. Blockade of activated microglia may slow cognitive deterioration occurring with inflammatory dementia.