Immunological studies of grain dust

Area of Science:

• Immunology
• Environmental Health
• Occupational Medicine

Background:

• Epidemiological studies suggest biological hazards in terminal grain elevators.
• Previous immunological assessments of grain workers yielded inconclusive results.
• A potential in vivo inflammatory mechanism for respiratory tracts upon inhaling airborne grain dust was investigated.

Purpose of the Study:

• To investigate the potential of airborne grain dusts to activate the complement system.
• To determine the specific complement pathway involved in grain dust-induced immune responses.
• To assess the inflammatory potential of grain dusts in the respiratory tract.

Main Methods:

• Activation of the alternative complement pathway by airborne grain dusts was assessed using precipitin-negative pooled normal human serum.
• Hemolytic complement consumption was quantified using CH100 immunodiffusion and CH50 tube assays.
• Complement activation was further analyzed using chelators (EGTA, EDTA) and serum from C4-deficient guinea pigs.
• Endotoxin levels were measured to assess their contribution to complement toxicity.

Main Results:

• Airborne grain dusts activated the alternative complement pathway in a dose-dependent manner.
• Complement consumption was confirmed via CH100 and CH50 assays.
• Activation was mediated by the alternative pathway, as evidenced by EGTA/EDTA effects and C4-deficient serum results.
• Aged settled dust and aqueous rye extracts also demonstrated activity against the alternative complement pathway.
• Complement toxicity was independent of endotoxin levels.

Conclusions:

• Airborne grain dusts can activate the alternative complement pathway, presenting a potential inflammatory insult to the respiratory tract of grain workers.
• The alternative complement pathway is a key mediator of the immune response to grain dust.
• The persistent activity of aged dust suggests a long-term occupational hazard.