Inhalation of horseradish peroxidase by rabbits withspecific IgE antibodies results in release into the circulation ofplatelet-activating factor and in lung lesions. Clin Immunol Immunopathol.

To further assess the role "in vivo" of platelet activating factor (PAF) in immediate hypersensitivity reactions in the lung, rabbits with either an IgE or an IgG response against horseradish peroxidase (HRP) were challenged with the antigen by aerosol for 1 hour. The animals were sacrificed 30 minutes after termination of the inhalation. The following observations were made: Upon inhalation of HRP, rabbits with circulating IgE antibodies showed signs of respiratory distress and released PAF into the circulation. The highest levels of circulating PAF were measured 20 to 30 minutes after the start of inhalation. PAF may contribute to the lung lesions found in these animals. Rabbits with IgG antibodies did not develop any early abnormalities upon challenge with HRP, this despite the fact that in some animals circulating specific IgE-sensitized basophils could be demonstrated. Anti-HRP IgG was able to block the "in vitro" degranulation of specific IgE-sensitized basophils when challenged with HRP.