Activation of microglia in HIV-1 infected brains is not dependent on the presence of HIV-1 antigens.

The activation pattern of microglia in the cerebral cortex of AIDS patients with the neuropathological diagnosis of HIV-1 encephalitis was investigated by immunohistochemistry and morphometry. The number of activated microglial cells in the grey and white matter of five cortical regions was determined. In the grey and white matter of all cortical regions a significant increase in the number of microglial cells was demonstrated in HIV-1 infected brains. Moreover, the activation of microglia was not correlated with the presence of HIV-1 antigen in the brain region. The data show a significantly increased number of microglia in HIV-1 infected brains. These activated microglial cells could, among others, be those cells producing cytotoxic factors which, in turn, cause brain damage.