Pneumocystis carinii: the art and science of survival in the hostile environment of the alveolar spaces.

Pneumocystis carinii remains an important cause of pneumonia in immunocompromised patients, particularly in those who have acquired immune deficiency syndrome. Potential mechanisms by which P. carinii escapes elimination by lung defenses and proliferates are discussed. Evidence indicates that P. carinii attachment to alveolar epithelium is an important event in the establishment of infection and occurs through a variety of means. The binding of the organisms appears to be injurious to alveolar epithelial cells. Proliferation of the organism is associated with an ineffective and at times detrimental host inflammatory response. Additional studies indicate that P. carinii has the ability to invade tissues. Future investigations using new methodologies and strategies will be required to fully control this pathogen.