Farmer's lung often presents clinically as recurring acute episodes several hours after exposure to moldy hay. During these episodes the blood neutrophil count increases. Because activated neutrophils release toxic
oxygen metabolites and
proteinases, we hypothesized that the pulmonary reaction in
farmer's lung may be induced by the secretory products of activated neutrophils. To evaluate this concept, we quantified the respiratory burst of separated blood neutrophils from patients with
farmer's lung (n = 12) during standardized exposure tests with moldy hay. The respiratory burst of these cells was evaluated by measuring
zymosan-stimulated and
lucigenin-amplified chemiluminescence (CL). Asymptomatic farmers (n = 12) and normal volunteers with no prior exposure to moldy hay (n = 15) were used as control subjects. As expected, following exposure in the group of patients with
farmer's lung, striking changes in VC, TLCO, and PaO2 were observed, whereas there were only minor changes in these parameters in both control groups. In all three groups a considerable increase in the blood leukocyte count was observed. The CL response of the blood neutrophils from patients with
farmer's lung 6 h after exposure was significantly higher than before or 1 h after exposure (p < 0.05 for both comparisons), whereas there was no significant change in the CL response in either control group during the observation period. Our results indicate that
antigen inhalation induces an increase in the number of circulating neutrophils in patients and controls, but in patients with an acute episode of
farmer's lung the neutrophils are primed for an enhanced respiratory burst and may thereby damage the lung.