Radiation Biology and Medicine

Young Beagle dogs were exposed by inhalation to aerosols of ²³⁹PuO₂ and observed for their lifespans as part of a large, ongoing study of the biological effects of inhaled radionuclides. The purpose of our study was to compare certain immune responses of the ²³⁹PuO₂-exposed dogs at middle age (7–10 years old) and old age (12–14 years old), with those of unexposed, age-matched or young (3–4 years old) animals. Some of the aged, exposed dogs had developed lung tumours. Lymphocyte proliferative responses to phytohaemagglutinin (PHA) were lower in aged control dogs than in either young or middle-aged control dogs. Both aged and middle-aged, radiation-exposed dogs had decreased responses to PHA when compared to age-matched controls. Responses to concanavalin A (Con A) were not affected by age in control dogs, but tended to decrease in the oldest group of radiation-exposed dogs. Responses to both PHA and Con A were severely depressed in tumour-bearing dogs. The cytolytic activity of natural killer cells was not affected by age, radiation exposure, or tumour presence. We concluded that inhalation of ²³⁹PuO₂ by young Beagle dogs resulted in an earlier-than-normal decrease in the ability of T cells to respond to mitogenic stimulation. In other words the depressed responses to PHA that were observed might represent radiation-induced, accelerated ageing of the T cell response.