1. Institute for Experimental Immunology, University Hospital Zurich, Schmelzbergstrasse 12, 8091 Zurich, Switzerland.
2. Max Planck Institute for Immunobiology, Freiburg, Germany.
3. M. Suter, Institute for Virology, University of Zurich, Switzerland.
4. F. Brombacher, Department of Immunology, Groote Schuur Hospital, University of Cape Town, 7925 Cape Town, South Africa.