Sterols of Pneumocystis carinii hominis Organisms Isolated from Human Lungs

The opportunistic pathogenPneumocystis carinii causes pneumonia (P. carinii pneumonia, or PCP) in immunocompromised individuals such as AIDS patients. Rat-derivedP. carinii carinii organisms have distinct sterols which are not synthesized by mammals and not found in other microbes infecting mammalian lungs. The dominant sterol present in the organism is cholesterol (which is believed to be scavenged from the host), but other sterols inP. carinii carinii have an alkyl group at C-24 of the sterol side chain (C28 and C29 24-alkylsterols) and a double bond at C-7 of the nucleus. Recently, pneumocysterol (C32 ), which is essentially lanosterol with a C-24 ethylidene group, was detected in lipids extracted from a formalin-fixed humanP. carinii -infected lung, and its structures were elucidated by gas-liquid chromatography, mass spectrometry, and nuclear magnetic resonance spectrometry in conjunction with analyses of chemically synthesized authentic standards. The sterol composition of isolatedP. carinii hominis organisms has yet to be reported. IfP. carinii from animal models is to be used for identifying potential drug targets and for developing chemotherapeutic approaches to clear human infections, it is important to determine whether the 24-alkylsterols of organisms found in rats are also present in organisms in humans. In the present study, sterol analyses ofP. carinii hominis organisms isolated from cryopreserved humanP. carinii -infected lungs and from bronchoalveolar lavage fluid were performed. Several of the same distinct sterols (e.g., fungisterol and methylcholest-7-ene-3β-ol) previously identified inP. carinii carinii were also present in organisms isolated from human specimens. Pneumocysterol was detected in only some of the samples.