Pneumocystis carinii organisms from in vitro culture are highly infectious to the nude rat

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Abstract
Many in vitro systems have been used to cultivatePneumocystis, but only limited parasite growth has been obtained by different authors. A reliable in vitro system enabling a sustained propagation ofPneumocystis appears to be an important condition for a better definition of the transmission ofP. carinii pneumonia. In this work,Pneumocystis in vitro culture was performed on monolayers of L2 rat lung epithelial-like cells. Ultrastructural assessment revealed that culture parasites were structurally intact.Pneumocystis culture samples were intratracheally inoculated into corticosteroid-treated nude rats (nonlatently infected byP. carinii), which developedP. carinii pneumonia at 40 days postinoculation. The infectious power of parasites obtained in vitro was 7–10 times higher than that of parasites freshly extracted from parasitized rat lung. In summary, the present results show that it is possible to obtain in vitro highly infectiousPneumocystis forms, and this study provides a promising infectivity test for use by investigators working onPneumocystis in vitro systems.