Interactions of complement with an extract of airborne spring wheat dust.

The inhalation, by grain elevator workers, of airborne grain dusts can lead to pulmonary problems. Complement, which is present in human airways, can interact with various grain dusts, producing activation products that have been shown to participate in the inflammatory reaction. Because of this apparent connection between grain-dust inhalation, complement activation, and respiratory difficulties, we are studying the reaction of an aqueous extract of spring wheat dust (swd) with human complement. The swd extract activates both the classical and alternative pathways; it acts on purified C2 to inhibit it, and it reacts with undiluted serum to consume C4 with kinetics significantly different from those shown by a "typical" antigen-antibody complex (sensitized sheep erythrocytes). Enzyme susceptibility experiments suggest that the alternative and classical pathway activators of swd extract are neither protein nor nucleic acid; periodate oxidation indicates these substances are carbohydrate, and gel filtration suggests they are macromolecular. Enzyme vulnerability also indicates that the C2 inhibitor of swd extract is ribonucleic acid. Although endotoxin is present in swd extract, a gel-filtration experiment showed that a major fraction of the complement reactivity was not associated with this substance.