CD4 and HIV-1 infection: Published reports focusing on the utilisation of the CD4 receptor and the CCR5 and CXCR4 co-receptors for HIV-1 infection in trophoblast cells are contradictory: some evidence suggests that the virus makes use of the receptors for membrane fusion [27], while other reports suggest that HIV-1 entry in trophoblast cells occurs independently of the CD4 receptor [28] or via an, as yet undefined, endocytic pathway [27,29,30].