Experimental production of pulmonary granulomas. IV. Eosinophilic granuloma.

Pulmonary granulomas induced in rabbits by the endobronchial instillation of mycobacterial chemical fractions were re-examined for eosinophilic infiltration. Delayed type hypersensitivity reactions either of tuberculin type or of wax D type did not induce but rather suppressed eosinophilic infiltration in the inflamed area, although some peptidoglycans which are antigenic for the induction of immediate hypersensitivity and fatty acid fractions were weak stimulators of eosinophilic infiltration. Bacterial endotoxin, LPS, was a potent stimulator. It was found that some long chain fatty acids can cause severe eosinophilic infiltration in the induced granulomas. Arachidonic acid was the most active of those examined, so the activity of its metabolites was tested and PGE2 was found to be most active. As the eosinophilic infiltration was markedly suppressed in animals treated with a cyclooxygenase inhibitor (aspirin), the stimulators of eosinophilic infiltration were not fatty acids themselves but their metabolites, PGE2 and some others. The site of permeation of eosinophils from the circulation was found to be arteriolar in the inflamed lung. The granulomatous lesion with eosinophilic infiltration in rabbits is discussed to shed light on the aetiology of eosinophilic granuloma in the human lung.