Infection of Neonatal Mice with Sindbis Virus Results in a Systemic Inflammatory Response Syndrome

Laboratory strains of viruses may contain cell culture-adaptive mutations which result in significant quantitative and qualitative alterations in pathogenesis compared to natural virus isolates. This report suggests that this is the case with Sindbis virus strain AR339. A cDNA clone comprising a consensus sequence of Sindbis virus strain AR339 has been constructed (W. B. Klimstra, K. D. Ryman, and R. E. Johnston, J. Virol. 72:7357–7366, 1998). This clone (pTR339) regenerates a sequence predicted to be very close to that of the original AR339 isolate by eliminating several cell culture-adaptive mutations present in individual laboratory strains of the virus (K. L. McKnight et al., J. Virol. 70:1981–1989, 1996). It thus provides a unique reagent for study of the pathogenesis of Sindbis virus strain AR339 in mice. Neonatal mouse pathogenesis of virus (TR339) generated from the pTR339 clone was compared with that of virus from a cDNA clone of the cell culture-passaged laboratory AR339 strain, TRSB, and virus from a clone of a more highly cell culture-adapted strain, HRsp (Toto 50). The sequence of TRSB differs from the consensus at three coding positions, while Toto 50 differs at eight codons and one nucleotide in the 5′ nontranslated region. Both cell culture-adapted strains contain mutations associated with heparan sulfate (HS)-dependent attachment to cells (W. B. Klimstra, K. D. Ryman, and R. E. Johnston, J. Virol. 72:7357–7366, 1998). TR339 caused 100% mortality with an average survival time (AST) of 1.7 ± 0.25 days. While TRSB also caused 100% mortality, the AST was extended to 2.9 ± 0.52 days. The more extensively cell culture-adapted virus Toto 50 caused only 30% mortality with an AST extended to 11.0 ± 4.8 days. TRSB and TR339 induced high serum levels of alpha/beta interferon, gamma interferon, tumor necrosis factor alpha, interleukin-6, and corticosterone and induced pathology reminiscent of lipopolysaccharide-induced endotoxic shock, a type of systemic inflammatory response syndrome. However, the reduced intensity of this response in TRSB-infected mice correlated with the increased AST. Toto 50 failed to induce the shock-like cytokine cascade. In situ hybridization studies indicated that TR339 and TRSB replicated in identical tissues, but the TRSB signal was less widespread at early times postinfection. While Toto 50 also replicated in similar tissues, the extent of replication was severely restricted and mice developed lesions characteristic of encephalitis. A single mutation in TRSB at E2 position 1 (Arg) conferred HS-dependent attachment to cells and was associated with reduced cytokine induction and extended AST in vivo.