Immune complex-mediated lung injury produced by horseradish peroxidase (HRP) and anti-HRP antibodies in rats.

Horseradish peroxidase (HRP) was administered intratracheally to rats with circulating autologous or heterologous anti-HRP antibodies. Intrapulmonary immune complexes containing HRP, anti-HRP antibodies, but no C3, were detected by immunofluorescence from 1 hour to 48 hours with a maximum of 6 hours after antigenic challenge. The concomitant hemorrhagic alveolitis characterized by fibrin deposits and infiltration by polymorphs and macrophages was also maximal after 6 hours. At the ultrastructural level, HRP was easily detected, and HRP-containing immune deposits were demonstrated along the basement membrane in subepithelial and subendothelial localization and in interstitial spaces. These findings suggest a C3 independent mechanism for lung injury mediated by immune complexes formed in situ.