What is the pathogenesis of Pneumocystis jiroveci pneumonia (PJP)?

Updated: Apr 24, 2019
  • Author: Shelley A Gilroy, MD, FACP, FIDSA; Chief Editor: Pranatharthi Haran Chandrasekar, MBBS, MD  more...
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Disease occurs when both cellular immunity and humoral immunity are defective. Once inhaled, the trophic form of Pneumocystis organisms attach to the alveoli. Multiple host immune defects allow for uncontrolled replication of Pneumocystis organisms and development of illness. Activated alveolar macrophages without CD4+ cells are unable to eradicate Pneumocystis organisms. Increased alveolar-capillary permeability is visible on electron microscopy.

Physiologic changes include the following:

  • Hypoxemia with an increased alveolar-arterial oxygen gradient

  • Impaired diffusing capacity

  • Changes in total lung capacity and vital capacity

There have been reports of PJP occurring as part of the immune reconstitution syndrome. [9, 10]

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