[1] Hop Edouard Herriot, F-69437 Lyon 03, France
[2] Roche Milano Ric, I-20123 Milan, Italy
[3] Free Univ Brussels, Hop Erasme, Serv Immunol, B-1070 Brussels, Belgium
[4] Fed Agcy Sera & Vaccines, Paul Ehrlich Inst, Dept Immunol, D-63225 Langen, Germany
[5] Univ Oxford, Sir William Dunn Sch Pathol, Oxford OX1 3RE, England