Immunopathologic aspects of Pneumocystis carinii pneumonia in infants as revealed by immunofluorescence and electron microscopy.

Lung tissue, lymph nodes, and spleen from infants 4-15 weeks old who died of Pneumocystis carinii pneumonia were studied by immunofluorescence and immunoelectron microscopy. The results strongly suggest that antibodies to P. carinii synthetized in lungs by inflammatory infiltrates and in regional lymph nodes are essential in the elimination of P. carinii from infected lungs through their opsonization of the P. carinii organisms. Disintegration of P. carinii conglomerates subsequent to the binding of complement preceded their phagocytosis by lung alveolar macrophages. The immunomorphologic findings strongly supported the hypothesis that the replication of P. carinii at the rate leading to clinical symptoms is due to impaired and delayed synthesis both of antibodies to P. carinii and of complement.