Stromal-cell-derived factor 1 prevents the emergence of the syncytium-inducing phenotype of HIV-1 in vivo.

In a correlative study, the mean plasma level of the chemokine stromal-cell-derived factor 1 (SDF-1) was lower in subjects with syncytium-inducing (SI) than in subjects with non-syncytium-inducing (NSI) HIV isolates, regardless of the CD4 cell count or when compared with HIV-negative individuals. Individuals with high SDF-1 had an 81% probability of having an NSI virus phenotype compared with individuals with lower SDF-1. Increased expression of SDF-1 may help explain why the more pathogenic SI HIV-1 variants do not appear in some individuals.