Purple acid phosphatase of human brain macrophages in AIDS encephalopathy

Brains from AIDS patients with an HIV-induced encephalopathy but without opportunistic infections or indications for an inflammation were studied by immuno- and enzyme-histochemical methods. It was found that the macrophages of these brains expressed a lysosomal tartrate-resistant acid phosphatase which gave a good immunological cross-reaction with an antibody to the well-characterized iron-containing bovine spleen purple acid phosphatase, belonging to the group of purple phosphatases, which are regarded as a marker for a special phenotype of activated macrophages. It was discussed that the numerous brain macrophages found in AIDS encephalopathy derive from latently infected monocytes which are believed to be drawn to the brain from the bloodstream.