Serial indium-111-labelled IgG biodistribution in rat Pneumocystis carinii pneumonia: a tool to monitor the course and severity of the infection.

To study the effect of new therapeutic strategies, we developed an animal model to monitor the course and severity of experimental Pneumocystis carinii pneumonia (PCP) in rats. P. carinii density scores in Giemsa-stained impression smears were used to follow P. carinii load. Indium-111 labelled IgG scintigraphy and biodistribution, histology of paraffin-embedded tissue sections, lung/body weight (L/B wt) ratio and cell count and differentiation of broncho-alveolar lavage (BAL) fluid were used as parameters of host inflammatory response. Statistically significant differences in L/B wt ratio, number of neutrophils in BAL fluid, P. carinii density score, histological extent of inflammation and 111In-IgG accumulation in the lung were seen between the rats sacrificed at various time points. 111In-IgG accumulation in the lung correlated well with L/B wt ratio and P. carinii density score and correlated moderately with number of neutrophils in BAL fluid and with the histological extent of inflammation.