Macrophage tropism of human immunodeficiency virus type 1 isolates from brain and lymphoid tissues predicts neurotropism independent of coreceptor specificity

The viral determinants that underlie human immunodeficiency virus type 1 (H IV-1) neurotropism are unknown, due in part to limited studies on viruses i solated from brain. Previous studies suggest that brain-derived viruses are macrophage tropic (M-tropic) and principally use CCR5 for virus entry. To better understand HIV-1 neurotropism, we isolated primary viruses from auto psy brain, cerebral spinal fluid, blood, spleen, and lymph node samples fro m AIDS patients with dementia and HIV-1 encephalitis. Isolates were charact erized to determine coreceptor usage and replication capacity in peripheral blood mononuclear cells (PBMC), monocyte-derived macrophages (MDM), and mi croglia. Env V1/V2 and V3 heteroduplex tracking assay and sequence analyses were performed to characterize distinct variants in viral quasispecies. Vi ruses isolated from brain, which consisted of variants that were distinct f rom those in lymphoid tissues, used CCR5 (R5), CXCR4 (X4), or both corecept ors (R5X4). Minor usage of CCR2b, CCR3, CCR8, and Apj was also observed. Pr imary brain and lymphoid isolates that replicated to high levels in MDM sho wed a similar capacity to replicate in microglia. Six of 11 R5 isolates tha t replicated efficiently in PBMC could not replicate in MDM or microglia du e to a block in virus entry. CD4 overexpression in microglia transduced wit h retroviral vectors had no effect on the restricted replication of these v irus strains. Furthermore, infection of transfected cells expressing differ ent amounts of CD4 or CCR5 with M-tropic and non-M-tropic R5 isolates revea led a similar dependence on CD4 and CCR5 levels for entry, suggesting that the entry block was not due to low levels of either receptor. Studies using TAK-779 and AMD3100 showed that two highly M-tropic isolates entered micro glia primarily via CXCR4. These results suggest that HIV-1 tropism for macr ophages and microglia is restricted at the entry level by a mechanism indep endent of coreceptor specificity. These findings provide evidence that M-tr opism rather than CCR5 usage predicts HIV-1 neurotropism.