Medline ® Abstracts for References 1,2

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. Warning 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 greater than or equal to 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. This cellular, as contrasted with humoral, immunity decreases with advancing age, which may account for a propensity to reactivation of VZ virus.

The clinicoepidemiologic features of varicella-zoster virus and herpes simplex virus latency are clearly distinctive. These differences indicate that each virus has evolved a unique strategy to ensure the establishment and maintenance of latency and to reactive therefrom. Indeed, current data reveal divergent pathogenetic and molecular biologic properties that may account for the clinicoepidemiologic characteristics that distinguish recurrent infections with these herpesviruses.