Immunoglobulin G4 in pigeon breeder's disease

Immunoglobulin G4 has previously been implicated in the pathogenesis of pigeon breeder's disease (PBD), a form of hypersensitivity pneumonitis associated with inhalation of pigeon antigens. We investigated the presence of IgG4 antibody to antigens in pigeon dropping extracts (PDE) in the lungs of pigeon breeders. Seven of these subjects had symptoms of PBD and eight others had no symptoms. IgG4 antibody to PDE was compared with IgG3 levels because both were relatively minor subclasses, but IgG3 is not considered reaginic whereas IgG4 is. An increase in IgG4 antibody relative to IgG3 would therefore be considered a selective increase and suggest a role for this subclass in the development of PBD. Our results, however, indicated that pigeon breeders without symptoms had significantly higher levels of serum IgG4 and that there were no significant differences with regard to the lavage fluid levels of IgG4, IgG3, or total IgG antibody in the two groups of subjects. A tendency of higher IgG4 antibody levels was found in lavage fluid from subjects without symptoms. These results do not support the hypothesis that IgG4 may act as a reaginic trigger in the development of PBD symptoms.