Lipid transfer from human epithelial cells to Pneumocystis carinii in vitro

Pneumocystis carinii lipids are similar to host lipids, but it is not known if some of these lipids are acquired from host cells. The ability of P. carinii to incorporate a fluorescent fatty acid analogue (Bodipy-C12) was analyzed, the metabolism of the incorporated lipid by P. carinii was characterized, and lipid transfer from human alveolar epithelial cells (A549) to P. carinii was investigated. Both P. carinii and A549 cells incorporated exogenous Bodipy-C12 in a concentration-dependent manner. Biochemical analysis of labeled P. carinii revealed incorporation of Bodipy-C12 into complex lipid classes. Incubation of unlabeled P. carinii with Bodipy-C12-labeled A549 cells demonstrated lipid transfer to P. carinii, a process facilitated by attachment. These data suggest that P. carinii can incorporate and modify an exogenous fluorescent lipid. The observed transfer of lipid from A549 cells to P. carinii provides important insight into the interaction of this organism with alveolar epithelial cells.