Morphology and distribution of HIV-1 gp41-positive microglia in subacute AIDS encephalitis - Pattern of involvement resembling a multisystem degeneration

Among 100 brains from patients with acquired immunodeficiency syndrome (AIDS), 33 brains (21 adults and 12 children) with histological evidence of subacute AIDS encephalitis were immunostained with one of the most sensitive antibodies to HIV-1 antigen, anti-gp41. Twenty-six (20/21 adults, 6/12 children) of the 33 brains showed pg41 positivity. Brains from children had fewer gp41-positive cells than brains from adults. The distribution of gp41-positive cells was characteristic. They were frequently detected and most numerous in the globus pallidus (medial > lateral). Although gp41-positive cells were prevalent, fewer were detected in the corpus striatum and thalamus. Of infratentorial areas involved, the ventral midbrain, especially the substantia nigra, and the dentate nucleus contained many positive cells. Lower levels of infections, often patchy, were noted in the cerebral and cerebellar white matter and pontine base. Gp41-positive cells were rarely seen in the cerebral cortex, medulla, spinal cord, leptomeninges, choroid plexus, ependyma, subependymal areas and endothelia. Besides immunoreactive macrophages and multinucleated cells, gp41-positive microglia with various morphological alterations were abundant in the deep cerebral gray matter, ventral midbrain and dentate nucleus. Most of these microglia were undetectable with conventional histological methods. We discuss the significance of the distribution of HIV-1-infected cells, especially microglia, with respect to cellular tropism and involvement of deep gray matter nuclei in a pattern reminiscent of a multisystem atrophy.