Correlation of cytotoxic activity in lungs to recovery of normal and gamma-irradiated cotton rats from respiratory syncytial virus infection.

Cotton rats (Sigmodon hispidus) that were exposed to 300, 600, or 900 rads of gamma irradiation and inoculated intranasally 2 days later with respiratory syncytial virus (RSV) exhibited prolonged virus shedding and delayed humoral and cytotoxic immune responses compared with comparably inoculated nonirradiated control rats. In nonirradiated animals and in animals exposed to 300 and 600 rads, levels of virus declined and then disappeared from the lungs during the period in which cytotoxic activity was maximal in the lungs of these animals. In contrast, in the group of cotton rats exposed to 900 rads of irradiation, local cytotoxic activity remained low throughout the 11-day observation period, and virus was not eliminated from the lungs. Although virus-neutralizing antibodies in serum and lavage fluids from these animals may have been involved, correlation of antibody concentrations with virus clearance from lungs was not as evident. These data suggest that cytotoxic effector cells have a positive role in eliminating RSV from the lungs of unprimed cotton rats.