[1] NIH, Viral Pathogenesis Sect, Viral Dis Lab, Bethesda, MD 20892 USA
[2] Washington Univ, Sch Med, Dept Pathol, St Louis, MO 63110 USA
[3] Washington Univ, Sch Med, Dept Immunol, St Louis, MO 63110 USA
[4] Washington Univ, Sch Med, Dept Med, St Louis, MO 63110 USA
[5] Washington Univ, Sch Med, Dept Mol Microbiol, St Louis, MO 63110 USA
[6] Purdue Univ, Dept Biol Sci, W Lafayette, IN 47907 USA