Immune complex disease in guinea pig lungs: elicitation with pigeon serum

Immune complex- and T cell-mediated reactions to organic antigens appear to contribute to the pathogenesis of hypersensitivity pneumonitis in humans. Because pigeon serum is one of the reagents used by clinicians to diagnose this disease, we assessed its potential to elicit immune complex-mediated pulmonary inflammation in guinea pigs. Animals were immunized with different concentrations of pigeon serum protein emulsified in complete Freund's adjuvant, and serums were collected at 4-day intervals after the booster injection. The largest amounts of tissue-fixing (IgG1) and complement-fixing (IgG2) antibodies to pigeon serum were detected in guinea pigs immunized with 1.0 mg of pigeon serum protein 20 to 24 days after the secondary immunization. Therefore, the responses of these animals and of recipients of serum from these animals to aerosol challenge with either homologous (pigeon serum) or heterologous (bovine gamma globulin) immunogen was investigated. Actively and passively immunized guinea pigs developed pulmonary inflammation only after exposure to aerosolized pigeon serum. However, lesions were not observed in the lungs of complement-deficient recipients of immune serum that had inhaled homologous immunogen. These observations suggest that such pigeon serum-elicited pulmonary inflammation in guinea pigs is a manifestation of a complement-dependent, humoral-immune mechanism of pathogenesis and thus is consistent with an immune complex disease.