CXCR4 and infection: Inhibition of HIV-1 IIIB (a virus utilizing CXCR4 as cellular coreceptor = X4 virus) and HIV-1 BaL (a virus utilizing CCR 5 as cellular receptor = R5 virus) [8,26] infection, respectively, of TZM-bl cells [19] by polymeric candidate microbicides in the absence or presence of SP (final concentration 33.3%) was investigated.