Hypersensitivity pneumonitis in nonhuman primates. I. Studies on the relationship of immunoregulation and disease activity.

We investigated the relationship of immunoregulation to disease activity in a nonhuman primate model of pigeon breeder's disease. Two Macaca arctoides monkeys developed classical symptoms of hypersensitivity pneumonitis after sensitization and prolonged bronchial challenge, whereas 2 other monkeys remained asymptomatic after in vivo challenge. There were no differences in the percentages of T cells, B cells, monocytes, or FC gamma-bearing T cells between symptomatic and asymptomatic animals. Nonetheless, we found a population of concanavalin A-induced, pigeon serum- (PS) induced, and spontaneous T cells that functioned as suppressor cells in autologous in vitro co-cultures in asymptomatic animals that were missing or nonfunctional in symptomatic animals. Monocyte suppressors functioned in both groups. We used low-dose total body irradiation (TBI) to inactivate T suppressor cells. Fifteen radiation units of TBI caused no change in the physical activity, routine chemistries, or blood counts of the 4 animals. After TBI, however, the previously asymptomatic animals developed fever, tachypnea, and signs of pulmonary congestion after in vivo challenge with PS. There was no change in the response to challenge in the symptomatic group. This altered response to in vivo challenge in the previously asymptomatic group persisted for 2 wk after TBI. During this period the difference in vitro immunoregulatory activity between Con A-induced, PS-induced, and spontaneous T cells in symptomatic and asymptomatic animals disappeared. Monocyte suppressors, however, continued to function in both groups after TBI. These data suggest that the monkey is an appropriate model for studies of human HP and that T cell immunoregulation may be an important element in the pathogenesis and disease activity of HP.