[1] Univ Alabama, Dept Med, Birmingham, AL 35294 USA
[2] Univ Alabama, Dept Pediat, Birmingham, AL 35294 USA
[3] Univ Alabama, Dept Pathol & Microbiol, Birmingham, AL 35294 USA
[4] Howard Hughes Med Inst, Birmingham, AL 35294 USA
[5] Univ Tennessee, Sch Med, Dept Pediat, Dept Immunol,St Jude Childrens Res Hosp, Memphis, TN 38105 USA