EXPERIMENTAL PULMONARY PNEUMOCYSTIS CARINII INFECTION IN RABBITS

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Abstract
Interstitial pneumonitis with many Pneumocystis organisms was found in rabbits treated with cortisone and antibiotics and instilled intranasally with a suspension of lung tissue from either a patient or a rabbit with this infection. Pulmonary lesions and organisms of similar severity and frequency were present in controls treated in the same manner but instilled with either saline or a boiled suspension of normal human lung tissue. The administration of antibiotics and infected rabbit lung suspension only produced less marked lung changes with fewer organisms. Rare organisms and minute foci of pneumonitis were encountered in normal rabbits which had received neither hormone, antibiotics nor inoculum. The pulmonary lesions in the cortisone treated rabbits resembled those of patients with the subclinical form of Pneumocystis pneumonitis. They did not reproduce the massive lesions of widespread Pneumocystis pneumonia. The findings indicate that latent pulmonary Pneumocystis infection was widespread in these rabbits but do not confirm the transmission of the disease. The activation of latent infection was dependent on an impairment of host resistance produced in these experiments most effectively by the administration of cortisone. The differences between the experimental lesions and those of typical Pneumocystis pneumonia suggest that in man an unknown defect of host defenses other than that induced by prolonged hormone administration accounts for the increased susceptibility to the infection. It is concluded that in the presence of widespread latent Pneumocystis infection the development of active disease in a manifestation of altered host resistance.