Several members of the chemokine receptor family are used together with CD4 for HIV-1 entry into target cells. T cell line-tropic (T-tropic) HIV-1 viruses use the chemokine receptor CXCR4 as a co-receptor, whereas macrophage-tropic (M-tropic) primary viruses use CCR5 (refs 2-6). Individuals with defective CCR5 alleles exhibit resistance to HIV-1 infection, suggesting that CCR5 has an important role in vivo in HIV-1 replication. A subset of primary viruses can use CCR3 as well as CCR5 as a co-receptor, but the in vivo contribution of CCR3 to HIV-1 infection and pathogenesis is unknown. HIV-1 infects the central nervous system (CNS) and causes the dementia associated with AIDS. Here we report that the major target cells for HIV-1 infection in the CNS, the microglia, express both CCR3 and CCR5. The CCR3 ligand, eotaxin, and an anti-CCR3 antibody inhibited HIV-1 infection of microglia, as did MIP-1beta, which is a CCR5 ligand. Our results suggest that both CCR3 and CCR5 promote efficient infection of the CNS by HIV-1.

Down's syndrome (DS) or trisomy 21 is the most common genetic cause of mental retardation. Development of the DS brain is associated with decreased neuronal number and abnormal neuronal differentiation, and adults with DS develop Alzheimer's disease. The cause of the neurodegenerative process in DS is unknown. Here we report that cortical neurons from fetal DS and age-matched normal brain differentiate normally in culture, but DS neurons subsequently degenerate and undergo apoptosis whereas normal neurons remain viable. Degeneration of DS neurons is prevented by treatment with free-radical scavengers or catalase. Furthermore, DS neurons exhibit a three- to fourfold increase in intracellular reactive oxygen species and elevated levels of lipid peroxidation that precede neuronal death. These results suggest that DS neurons have a defect in the metabolism of reactive oxygen species that causes neuronal apoptosis. This defect may contribute to mental retardation early in life and predispose to Alzheimer's disease in adults.