Immune responses to varicella-zoster in the aged

Abstract

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 mo. to 93 yr. Waning of cellular immunity, as examined by skin delayed hypersensitivity, began at 40 yr of age. Skin test responses to phytohemagglutinin remained positive into the 8th decade of life. In vitro lymphocyte stimulation responses to VZ were usually positive (stimulation index .gtoreq. 2.5) until age 60 yr, 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 9th and 10th decades of life. This was especially true 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.