[1] UCL, Div Infect & Immun, Dept Immunol, London W1T 4JF, England
[2] Royal Free Hosp, Dept Dermatol, London NW3 2QG, England
[3] Univ Arizona, Coll Med, Dept Immunobiol, Tucson, AZ 85719 USA
[4] Univ Arizona, Coll Med, Arizona Ctr Aging, Tucson, AZ 85719 USA