The CXC chemokine stromal cell-derived factor 1 is not responsible for CD8(+) T cell suppression of syncytia-inducing strains of HIV-1

Primary CD8(+) T cells from HIV+ asymptomatics can suppress virus production from CD4(+) T cells acutely infected with either non-syncytia-inducing (NSI) or syncytia-inducing (SI) HIV-1 isolates. NSI strains of HIV-1 predominantly use the CCR5 chemokine receptor as a fusion cofactor, whereas fusion of T cell line-adapted SI isolates is mediated by another chemokine receptor, CXCR4. The CCR5 ligands RANTES (regulated on activation, normal T cell expressed and secreted), macrophage inflammatory protein 1 alpha (MIP-1 alpha), and MIP-1 beta are HIV-1 suppressive factors secreted by CD8(+) cells that inhibit NSI viruses. Recently, the CXC chemokine stromal cell-derived factor 1 (SDF-1) nas identified as a ligand for CXCR4 and shown to inhibit SI strains. We speculated that SDF-1 might be an effector molecule for CD8(+) suppression of SI isolates and assessed several SDF-1 preparations for inhibition of MV-1(LAI)-mediated cell-cell fusion, and examined levels of SDF-1 transcripts in CD8(+) T cells. SDF-1 fusion inhibitory activity correlated with the N terminus, and the alpha and beta forms of SDF-1 exhibited equivalent fusion blocking activity. SDF-1 preparations having the N terminus described by Bleul et al. (Bleul, C.C., Fuhlbrigge, R.C., Casasnovas, J.M., Aiuti, A. & Springer, T.A. (1996) J. Exp. Med. 184, 1101-1109) readily blocked HIV-1(LAI)-mediated fusion, whereas forms containing two or three additional N-terminal amino acids lacked this activity despite their ability to bind and/or signal through CXCR4. Though SDF-1 is constitutively expressed in most tissues, CD8 T cells contained extremely low levels of SDF-1 mRNA transcripts (<1 transcript/5,000 cells), and these levels did not correlate with virus suppressive activity. We conclude that suppression of SI strains of HIV-1 by CD8(+) T cells is unlikely to involve SDF-1.