title: Histopathology ofPneumocystis cariniipneumonia in immunocompetent laboratory rats.
abstract: The occurrence of idiopathic pulmonary lesions in laboratory rats, characterized by lymphohistiocytic interstitial pneumonia with dense perivascular lymphoid cuffs, has been reported over the past decade. Although the term rat respiratory virus (RRV) was adopted to confer a putative viral etiology to the idiopathic pulmonary lesions, the etiology of this disease remains to be elucidated. Recently, inflammatory lesions have been observed in the lungs of immunocompetent laboratory rats similar to those previously described. Based on the latest evidence indicating thatPneumocystis carinii (P. carinii), and not putative RRV, causes infectious interstitial pneumonia in laboratory rats, the present study investigated whether the pulmonary lesions observed were caused byP. cariniiinfection. Male Sprague-Dawley rats, free of known pathogens, were introduced into a rat colony positive for RRV-type lesions. Routine histopathological examinations were performed on the rat lung tissues following exposure. The presence ofPneumocystisorganisms was confirmed using Grocott's methenamine silver (GMS) staining. At week 3 following introduction, a few small lymphoid aggregates were located adjacent to the edematous vascular sheath. By week 5, foci of dense perivascular lymphoid cuffing were observed. Multifocal lymphohistiocytic interstitial pneumonia and prominent lymphoid perivascular cuffs were observed between week 7 and 10. GMS staining confirmed the presence ofPneumocystiscysts. Thus, the results of the present study demonstrated thatP. cariniicaused lymphohistiocytic interstitial pneumonia in a group of laboratory rats. The observations strongly support the conclusion thatP. cariniiinfection in immunocompetent laboratory rats causes the lung lesions that were previously attributed to RRV.
authors.affiliation: Department of Pathology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 135-710, Republic of Korea ; Republic of Korea Air Force Aerospace Medical Center, Chungcheongbuk-do 363-849, Republic of Korea.
authors.forename: Hyun-Soo
authors.initials: HS
authors.lastname: Kim
authors.affiliation: Department of Pathology, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul 110-746, Republic of Korea.
authors.forename: Sung-Im
authors.initials: SI
authors.lastname: DO
authors.affiliation: Department of Pathology, School of Medicine, Kyung Hee University, Seoul 130-701, Republic of Korea.
authors.forename: Youn Wha
authors.initials: YW
authors.lastname: Kim
keywords: Pneumocystis carinii; interstitial pneumonia; lung; rat; rat respiratory virus