[1] GKT Sch Med & Dent, Rayne Inst, Dept Immunol, London SE5 9NU, England
[2] Hammersmith Hosp, Sch Med, Div Infect Dis, London, England
[3] GKT Sch Med & Dent, Publ Hlth Labs, Dept Virol, Dulwich, England
[4] Netherlands Red Cross, Blood Transfus Serv, Cent Lab, Dept Clin Viroimmunol, Amsterdam, Netherlands
[5] MRC, Human Immunol Unit, Inst Mol Med, Oxford, England
[6] UCL, Windeyer Inst, Dept Mol Pathol, Wohl Vir Ctr, London WC1E 6BT, England