Inhalation of grain dusts can cause symptoms of both acute and chronic bronchitis, which has been associated with a neutrophilic inflammatory response in the lung. Since this influx of neutrophils may potentially result in bronchial injury, mechanisms of neutrophil recruitment to grain dust were examined. Sterile, aqueous grain dust extracts were prepared from settled dusts of grain sorghum, corn, oats, and soybeans. The extracts were evaluated for their ability to directly attract human neutrophils using a blindwell neutrophil chemotaxis assay. Each extract was found to possess significant chemotactic activity compared to controls (p < 0.01). To evaluate if the dusts could attract neutrophils indirectly by activating humoral inflammatory mechanisms, the grain dust extracts were evaluated for their ability to activate the complement system. When incubated with normal human serum, each of the grain dusts caused cleavage of the complement proteins C3 and properdin factor B (PFB). Importantly, the grain dust extracts lead to the generation of C5a, a potent neutrophil chemoattractant generated by complement activation. Since activation of the alveolar macrophage to release chemotactic activity represents an additional indirect mechanism of neutrophil recruitment, an extract from grain sorghum dust was evaluated for its ability to stimulate guinea pig and human alveolar macrophages to release neutrophil chemotactic activity. The results demonstrate that supernatants obtained from alveolar macrophage cultured in the presence of grain sorghum dust extract possessed increased chemotactic activity compared to contols (p < 0.01). The depletion of endotoxin from grain sorghum dust extract preserved direct neutrophil chemotactic activity and the ability to activate complement, but significantly decreased the capacity of alveolar macrophages to release chemotactic activity for neutrophils. The ability of one particularly noxious dust, grain sorghum dust, to induce an acute inflammatory response in the lung was confirmed in a guinea pig model of grain dust exposure. Following intratracheal instillation of grain sorghum dust extract, both bronchoalveolar lavage and histological examination revealed intense recruitment of neutrophils compared to saline controls. These results suggest that grain dust exposure can result in an inflammatory response by both direct and indirect mechanisms.
ASJC Scopus subject areas
- Pulmonary and Respiratory Medicine