The long sought co-receptors for primate lentiviruses were identified as belonging to a large family of cell surface proteins - the seven transmembrane proteins. These proteins normally function as cell surface receptors for chemokines and other ligands. The families of genetically divergent Simian Immunodeficiency Viruses (SIV), which include the origins of HIV-1 and HIV-2, use simian and human chemokine receptors as their co-receptors. SIVmac, SIVsm, SIVagm and SIVcpz use monkey and human CCR5 for cell fusion and entry. Human-derived STRL33 (BONZO) and human-derived GPR-15 (BOB) are also used, but with variable efficiency. True primary strains of SIVsm, obtained from the naturally infected simian host, the sooty mangabey, use simian and human CCR5 in a strongly CD4 dependent manner. However, some brain and lymphoid isolates from the experimental simian host, the macaque use CCR5 independently of CD4. Unlike T cell line adapted (TCLA) CXCR4-tropic HIV strains (XR4 HIV), only a few laboratory SIV strains use CXCR4 for entry. Macaque and mangabey CXCR4 are fully functional, because they are highly efficient for entry of XR4 HIV. The CCR5 co-receptor is used by three of four SIV families tested thus far. The fourth family, represented by the isolate, S1Vrcm95GB1, is unique among SIV and HIV in its use of CCR2b but not CCR5.
Copyright 1998 Academic Press.