There has been much discussion regarding the classification of Pneumocystis jiroveci, formerly known as P. carinii.
P. carinii is found only in rat lungs and P. jiroveci is a pathogen only found in humans. P. jiroveci was erroneously classified as a protozoan, when in actuality it is a yeast-like fungus.
Pneumocystis pneumonia (PCP) or pneumocystosis causes pneumonia in human immunodeficiency virus (HIV) patients, immunosuppressed patients, and organ transplant recipients. In infected lungs, P. jiroveci is visualized as homogeneous rings corresponding to individual fungal cyst walls in intra-alveolar spaces.
P. jiroveci mouse monoclonal clone 3F6, is an IgM, kappa isotype antibody that requires enzyme-induced epitope retrieval (EIER) pretreatment with pepsin or heat-induced epitope retrieval (HIER) pretreatment with citrate buffer for demonstration of P. jiroveci.