[1] Univ Washington, Sch Med, Dept Immunol, Seattle, WA 98195 USA
[2] Univ Massachusetts, Sch Med, Howard Hughes Med Inst, Worcester, MA 01605 USA
[3] Univ Massachusetts, Sch Med, Dept Biochem & Mol Biol, Program Mol Med, Worcester, MA 01605 USA
[4] Yale Univ, Sch Med, Howard Hughes Med Inst, New Haven, CT 06520 USA
[5] Yale Univ, Sch Med, Immunobiol Sect, New Haven, CT 06520 USA