n :  a pneumonia that affects individuals whose immunological defenses have been compromised by malnutrition, by other diseases (as cancer or AIDS), or by artificial immunosuppressive techniques (as after organ transplantation), that is caused by a microorganism of the genus Pneumocystis (P. carinii) which shows up in specially stained preparations of fresh infected lung tissue as cysts containing six to eight oval bodies, and that attacks esp. the interstitium of the lungs with marked thickening of the alveolar septa and of the alveoli - abbr. PCP - called also pneumocystic pneumonia , Pneumocystis carinii pneumonitis  .
 
 
 
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