Target cells were incubated with or without HD5 or HNP1 at 14.7 μM in RPMI-0 for 2 hours at 37C° and then stained with two anti-CXCR4 mAbs that inhibit infection by X4 HIV-1 strains [37]: 12G5, a conformation dependent mAb directed against a bridging epitope spanning the first and second extracellular loops of CXCR4 [38], and 44717.111, a conformation-dependent mAb that recognizes CXCR4 with higher efficiency that 12G5 on both PM1 and primary T lymphocytes [39]. This evidence concerns the gene CXCR4 and infection.