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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.

Settled grain dust was collected from several active grain elevators in the Superior-Duluth areas of the United States. Particle size distribution (47% less than 5 micrometer) and endotoxin contamination (429 ng/gm) of the dust were similar to those reported for the airborne parent dust. Human complement uas activated in vitro in a dose-response manner which could be quantified. This hemolytic consumption was via the alternative pathway as defined by ethylenediaminetertraacetic acid/ethylene-glycol-bis-(beta-amino-ethyl ether) N,N'-tetraacetic acid (EDTA/EGTA) differential serum chelation, factor B conversion, and complement reductions in serum from guinea pigs deficient in C4. It is proposed that continuous low-dose exposure to aerosolized, biologically active rafter dust could contribute to the respiratory insult of grain workers.