Co-receptors for HIV-1 entry.

HIV-1 enters its target cells by fusion at the plasma membrane. The primary cellular receptor for HIV is CD4, but this molecule is insufficient to permit viral fusion. During 1996, the necessary entry co-factors (co-receptors or second receptors) were identified as being members of the seven-transmembrane-spanning receptor family fusin: CXCR4 for T-tropic strains and CCR5, principally, for M-tropic strains. The co-receptor functions of these proteins are inhibited by their natural alpha- and beta-chemokine ligands.