[1] Univ Zurich Hosp, Inst Expt Immunol, CH-8057 Zurich, Switzerland
[2] Rockefeller Univ, Lab Viral Immunobiol, New York, NY 10065 USA
[3] Northwestern Univ, Dept Microbiol Immunol, Feinberg Sch Med, Chicago, IL 60611 USA
[4] Northwestern Univ, Interdept Immunobiol Ctr, Feinberg Sch Med, Chicago, IL 60611 USA