A CCR5/CXCR4-independent coreceptor pathway on human macrophages supports efficient SIV Env-mediated fusion but not infection: Implications for alternative pathways of viral entry

Several coreceptors in addition to CCR5 and CXCR4 support immunodeficiency virus entry in transfected cells, but whether they could play a role in HIV -I pathogenesis is uncertain. To probe whether human macrophages express po tentially functional alternative entry pathways, we analyzed cell-cell fusi on and infection of primary macrophage by several SIVmac Envs. All Envs fus ed with normal macrophages. One, SIVmac316, also fused efficiently with mac rophages lacking CCR85, CCR5-independent fusion was not mediated by CXCR4 a nd was CD4 dependent, while CCR5-mediated fusion was partly independent of CD4. However, pseudotype virions carrying the SIVmac316 Env and HIV-I core could not infect macrophages through the CCR5-independent pathway, although they did infect wild-type macrophages. Thus, human macrophages possess an alternative coreceptor pathway that mediates SIV Env fusion but does not su pport infection. Macrophage entry pathways other than CCR5 and CXCR4 may ha ve limited potential in pathogenesis given their restricted capacity for in fection despite efficient fusion, (C) 2001 Academic Press.