Imaging of Pneumocystis carinii pneumonia with 111In-labelled non-specific polyclonal IgG: an experimental study in rats.

The relative sensitivity of imaging with 67Ga-citrate (67Ga) and non-specific human polyclonal IgG radiolabelled with 111In (111In-IgG) for the detection of Pneumocystis carinii pneumonia (PCP) was determined in rats. Pneumocystis carinii pneumonia was induced by low protein diet and dexamethasone. The course of the disease was monitored by serial imaging with 111In-IgG and 67Ga. Diffuse accumulation of both radiopharmaceuticals was observed in the lungs of infected animals (infection was verified by histological examination of the lungs), however, accumulation of 111In-IgG was consistently higher. In rats with early PCP, 111In-IgG imaging revealed pulmonary accumulation in animals with normal chest radiographs and 67Ga scans. In animals successfully treated for PCP, decreased pulmonary accumulation of 111In-IgG coincided with histological improvements. Several animals developed superinfection with bacteria or fungi. These animals had striking focal accumulation of 111In-IgG, in addition to the pattern of generalized uptake. Gallium concentration in these animals did not show this focal accumulation. These observations suggest that 111In-IgG may be useful for detecting PCP and pulmonary abscesses in the immunocompromised host.