[1] Scripps Res Inst, Dept Immunol IMM 2, La Jolla, CA 92037 USA
[2] Scripps Res Inst, Dept Mol Biol, La Jolla, CA 92037 USA
[3] Cornell Univ, Weill Med Coll, Dept Microbiol & Immunol, New York, NY USA
[4] Agr Univ Vienna, Inst Appl Microbiol, A-1180 Vienna, Austria