Age-related changes in the immune system of mice of eight medium and long-lived strains and hybrids. II. Short- and long-term effects of natural infection with parainfluenza type 1 virus (Sendai).

Studies on the effects of natural infection with parainfluenza type 1 virus (Sendai) on the immune system of 8 strains and hybrids of aging mice revealed that (a) 55 of 63 indices tested were abnormal as late as 8 months after the disappearance of clinical systoms, (b) thymus weight and cell indices and lymph node T cell activity still exhibited a statistically significant negative correlation with age following infection, and (c) immunologically immature young and immunodeficient old mice suffered more severe sequelae following viral infection than did adult or middle-aged mice as determined by accelerated decline of thymus indices, mortality, IgM Coombs' titer, and in the case of old mice, anemia. These findings suggest that chronic viral infection can accelerate immunologic aging and that viral infection in utero can suppress or retard the development of the T cell component of the immune system. In support of our previous study, they also suggest that the thymus regulates immunologic aging and that genetic factors regulating immunologic aging are not easily influenced by environmental factors.