The role of inflammation in respiratory impairment during Pneumocystis carinii pneumonia

Pneumocystis carinii remains an important cause of pneumonia in immunosuppressed hosts. Severe Pneumocystis pneumonia is characterized by an intense neutrophilic inflammatory response resulting in gas exchange abnormalities, diffuse alveolar damage, and respiratory failure. The inflammatory response directed against P. carinii involves a complex series of interactions between alveolar macrophages, CD4+ T lymphocytes, polymorphonuclear cells, and their various products. CD4+ T lymphocytes are crucial to host defense against P. carinii. Alveolar macrophages also provide essential functions that significantly enhance clearance of P. carinii infection. In addition, host proteins play an important role in augmenting the host inflammatory responses to this organism. Although essential for effective clearance of infection, excessive inflammatory responses also predispose the host to the development of lung injury and respiratory compromise. Understanding the complex processes involved in the host inflammatory response and its potential for causing lung injury may enable development of novel therapeutic approaches for this and other important fungal lung infections.