Carrier requirement for development of acute experimental hypersensitivity pneumonitis in the rabbit

Fluorescein isothiocyanate (FITC) conjugated to protein carriers was used to explore carrier dependence in an established rabbit model of acute hypersensitivity pneumonitis (HSP). Rabbits were immunized via toepads with either FITC-ovalbumin (OA) or FITC-human gamma-globulin (HGG) in complete Freund's adjuvant, and were aerosol challenged with homologous or heterologous conjugates 30 days later. Only those rabbits challenged with the homologous carrier developed acute HSP, despite the presence of comparable levels of anti-FITC antibodies in the sera of all groups. These findings indicate a strict carrier dependence in the pathogenesis of HSP in this model and provide further evidence that the mechanism of inflammation depends upon a cellular immune response.