[1] Vanderbilt Univ, Sch Med, Elizabeth B Lamb Ctr Pediat Res, Nashville, TN 37232 USA
[2] Vanderbilt Univ, Sch Med, Dept Microbiol & Immunol, Nashville, TN 37232 USA
[3] Vanderbilt Univ, Sch Med, Dept Pediat, Nashville, TN 37232 USA
[4] Univ N Carolina, Dept Biochem & Biophys, Chapel Hill, NC 27599 USA