[1] Columbia Univ Coll Phys & Surg, Dept Microbiol, New York, NY 10032 USA
[2] Yale Univ Med, Immunobiol Sect, New Haven, CT 06520 USA
[3] Univ Penn, Dept Pathobiol, Philadelphia, PA 19104 USA
[4] Yale Univ Med, Dept Cell Biol, New Haven, CT 06520 USA
[5] Yale Univ Med, Howard Hughes Med Inst, New Haven, CT 06520 USA
[6] Columbia Univ Coll Phys & Surg, Dept Biochem & Mol Biophys, New York, NY 10032 USA