Extracts of airborne grain dusts activate alternative and classical complement pathways.

This study investigated the action of aqueous extracts of airborne grain dusts on the human alternative and classical complement pathways. Extracts were shown to consume hemolytic complement in vitro in a dose-dependent manner. No relationship was determined between complement activity ranking and either protein or endotoxin levels. Differential serum chelation with EDTA or EGTA showed that the alternative pathways were activated, while hemolytic titers of the early complement components (C1, C4, C2 and C3) showed that the classical pathway was also involved. Extract-treated sera were chemotactic for human polymorphonuclear leukocytes and complement was required. The in vitro data suggest the potential for the in vivo contribution of the activation of the complement cascade (by either pathway) in eliciting pulmonary pathophysiology after the inhalation of airborne grain dusts.