P. carinii: the bronchoalveolar lavage can be stained with specific stains for trophozoites like Giemsa.
Clusters of typical pleomorphic trophozoites (1-3 micron) and cysts can be observed:
trophic forms appear with reddish nuclei and blue cytoplasm.
 
 

P. carinii: cysts have a thick wall: sometimes the wall appears as
a transparent outline with intracystic bodies.
 

P.carinii: with Giemsa stain cysts (approx. 5-8 µm in diameter) are variably stained.
Intracystic bodies are present in different numbers within the cysts.
Mature cysts have 8 intracystic bodies. Some cysts appear empty.

The trophozoites multiply slowly, extensively in the lungs and progressively fill the alveoli that are finally
stuffed by the foamy exudate. The classical exudate consists of clusters of Pneumocystis carinii,
degenerated cells, host proteins and few alveolar macrophages. H&E stain.
 

P.carinii: in tissue sections, the alveolar space appears filled by honeycombed material consisting
in clusters of P.carinii, host proteins and degenerated cells. A scanty inflammation is present.
Interstitial hyperplasia with edema and infiltration occur.H&E stain.
 

P. carinii: clusters of cysts are demonstrated in the alveolar space with stains which are selective
for the "parasite" wall methenamine silver and toluidine blue O. Open lung biopsy, silver methenamine stain.

P. carinii: clusters of cysts are demonstrated in the alveolar space.
Open lung biopsy, silver methenamine stain.
 

P. carinii: with higher magnification single cysts are visible within the cluster.
Open lung biopsy, silver methenamine stain.

Lung biopsy section stained with: The cysts are well recognizable as round, oval or flat bodies
of approx.4-5 µm in diameter. Gomori's  methenamine silver stain (GMS).
 

P.carinii: the sediment of the BAL can be stained with stains for the cysts wall such as
methenamine silver.The cysts are well recognizable as round, oval or flat bodies of
approx. 4-5 µm in diameter. Gomori's methenamine silver stain (GMS).
 
 

 Pneumocystis carinii trophozoites in broncho-alveolar lavage (BAL) material.  Giemsa stain.  T
he trophozoites are small (size: 1-5 µm), and only their nuclei, stained purple, are visible (arrows).
AIDS patient seen in Atlanta, Georgia.
 

Pneumocystis carinii cysts
 3 cysts in bronchoalveolar material, Giemsa stain; the rounded cysts (size 4-7 µm)
contain 6-8 intracystic bodies, whose nuclei are stained by Giemsa;the walls of
the cysts are not stained; note the presence of several smaller, isolated trophozoites

Pneumocystis carinii cysts
 cysts in lung tissue, silver stain; the walls of the cysts are stained black;
the intracystic bodies are not visible with this stain; baby who died with pneumonia in California.

Pneumocystis carinii cysts in broncho-alveolar lavage material; silver stain;
this greater magnification shows the irregular, saucer shape of the cysts.