Infection of NP-2/CD4/CCR5 cells with CBL23 and mndGB-1, but not with the GUN-7WT or HCM342 strains, was also partially blocked by the peptide, suggesting that the fMLF peptide may have inhibitory effects on infection of CCR5-positive cells by several strains of HIV/SIV. Here, CD4 is linked to infection.