Skin test reactivity and in vitro lymphocyte stimulation responses to varicella-zoster (VZ) were examined in a large normal population ranging in age from 6 months to 93 years. Waning of cellular immunity, as examined by skin delayed hypersensitivity, began at age 40 years. Skin test responses to phytohemagglutinin, however, remained positive into the eighth decade of life. In vitro lymphocyte stimulation responses to VZ were usually positive (stimulation index ≥ 2.5) until age 60 years, after which time levels, as observed with nonimmune individuals, were often demonstrated. Antibody levels, as measured by fluorescent antibody to membrane antigen, remained positive into the ninth and tenth decades of life. This was especially so with a history of reactivation (zoster) VZ infections, while skin test and in vitro responses were rarely positive in those individuals. Thus cellular, as contrasted with humoral, immunity decreases with advancing age, which may account for a propensity to reactivation of VZ virus.
(Arch Intern Med 1982;142:291-293)