Requirements for lymphocyte activation by unusual strains of simian immunodeficiency virus

When residues 17 and 18 in nef of simian immunodeficiency virus strain SIVmac239 were changed from RQ to YE, the resultant virus was able to replicate in peripheral blood mononuclear cell cultures without prior lymphocyte activation and without the addition of exogenous interleukin-2, caused extensive lymphocyte activation in these cultures, and produced an acute disease in rhesus and pigtail macaques (Z. Du, S. M. Lang, V. G. Sasseville, A. A. Lackner, P. O. Ilyinskii, M. D. Daniel, J. U. Jung, and R. C. Desrosiers, Cell 82:665-674, 1995), These properties are similar to those of the acutely lethal pathogen STVpbj14 but dissimilar to those of the parental SIVmac239, We show here that the single change of R to Y at position 17 in nef of SIVmac239 is sufficient to confer the full, unusual phenotype, Conversely, the lymphocyte-activating properties of STVpbj14 were lost by the single change of Y to R at position 17 of nef, The change of R17F or Q18E in STVmac239 nef did not confer the unusual in vitro properties, Since SIVpbj14 has a duplication of the NF-kappa B binding sequence in the transcriptional control region, we also constructed and tested strains of SIVmac239/R17Y with zero, one, and two NF-kappa B binding elements, We found no difference in the properties of SIVmac239/R17Y, either in cell culture or in vivo, whether zero, one, or two NF-KB binding sites were present, Thus, tyrosine at position 17 of nef is absolutely necessary for the unusual phenotype of SIVphj14 and is sufficient to convert SIVmac239 to a virus,vith a phenotype like that of SIVpbj14. Multiple NF-kappa B binding sites are not required for the in vitro properties or for acute disease.