Establishment of Pneumocystis carinii in various mouse strains using natural transmission to initiate infection.

A mouse model for Pneumocystis carinii has now been established in several strains of mice: C3Heb/FeJ, C3HeN, Balb/c, DBA/2N and athymic. In lieu of using invasive methods for initiating P. carinii infections, mice infected with P. carinii (seed mice) transmitted the disease to mice without latent infection via short term co-habitation. Acute infections in recipient mice developed approximately 5-6 wk after C3Heb/FeJ seeds were removed, while control unseeded litter-mates remained uninfected. This approach allows investigators to consistently transmit P. carinii to mice and to select the strain of mouse desired for use in a particular study.     

Generalized immune response to Pneumocystis carinii infection in the lung.

We studied inflammatory cells retrieved by bronchoalveolar lavage (BAL) from immunocompromised patients with or without Pneumocystis carinii pneumonia (PCP). Twenty-four patients with PCP, and 20 patients without PCP underwent lavages of both an uninvolved lobe and the lobe involved in pulmonary infection. Patients without P. carinii, had a significant increase (p less than 0.02) in the percentages of neutrophils (22 +/- 7.1%, mean +/- SEM) and lymphocytes (16 +/- 3.8%) in the involved lobe compared to those in the uninvolved area (neutrophils: 9 +/- 4.8%; lymphocytes: 10 +/- 2.4%). Patients with PCP, had no differences between the % neutrophils or % lymphocytes in the involved vs. uninvolved lobes. Patients with PCP had more (p less than 0.01) P. carinii in the upper lobe (23 +/- 4.6 P. carinii clusters/500 cells) than the middle lobe (11 +/- 3.6). In PCP, despite regional infections, there was a diffuse inflammatory response.     

Pneumocystis carinii infection in corticosteroid-treated cats

Corticosteroids were administered to produce Pneumocystis carinii infection in cats. Six of 10 cats, injected intramuscularly for 97-141 days with 2 mg/cat twice weekly of betamethasone sodium phosphate, developed a light infection with P. carinii. Six of 7 cats, injected intramuscularly for 11-168 days with 10-25 mg/cat weekly of prednisolone acetate, also developed a light infection with P. carinii. There was no significant difference in the infection rate between the sexes and ages of the cats. Using Giemsa staining and Gomori's methenamine silver nitrate stain, P. carinii organisms were indistinguishable morphologically from human and rat P. carinii. The cysts and trophozoites were usually present singly or in small groups, and they always were adhering to the periphery of alveoli. The inflammatory changes were inconspicuous except for the fact that alveolar macrophages often were seen. Corticosteroid-treated cats should be useful in the study of experimental P. carinii infection. This is the first reported case of experimentally induced P. carinii infection in cats.     

Cellular immune response in Pneumocystis carinii infection

Pneumocystis carinii is an important pulmonary pathogen causing disease in immunocompromised individuals. The majority o f conditions predisposing to Pneumocystis pneumonia are associated with profound defects in cellular immunity. Although our understanding o f the host response to the organism is still limited, advances in antigen preparation and the availability o f animal models have permitted an improved understanding of some aspects o f the cell-mediated immune response to Pneumocystis. In this review, George Smulian and Sue Theus will highlight recent advances in our knowledge regarding the role of macrophages, T cells and cytokines in the response to the organism.     

Pneumocystis carinii polyamine catabolism.

DL-alpha-Difluoromethylornithine (DFMO) causes polyamines of the AIDS-associated opportunistic pathogen Pneumocystis carinii to diminish 15 times more rapidly than mammalian host cells. The proposed mechanism was that, unlike mammalian cells, P. carinii is unable to regulate polyamine catabolism when synthesis is blocked. To test this, the responses of the polyamine catabolic enzymes spermidine/spermine acetyltransferase (SSAT) and polyamine oxidase (PAO) were determined using a new high-performance liquid chromatography assay to measure the products of these enzymes. The specific activities in untreated Pneumocystis carinii were 1.78 +/- 0.5 pmol min(-1) mg protein(-1) for SSAT, similar to mammalian cells, and 6.42 +/- 0.8 pmol min(-1) mg protein(-1) for PAO, 19% of that of mammalian cells. DFMO treatment for 12 h caused reductions of only 11 and 4% in SSAT and PAO, respectively, despite polyamine reductions of 94, 96, and 90% for putrescine, spermidine, and spermine, respectively. The P. carinii SSAT K(m) value of 25 microM spermidine is 20% of that of mammalian cells, and the PAO K(m) value of 14 nM N(1)-acetylspermidine is 0.01% of that of mammalian cells. Acetylated polyamines continue to be lost from P. carinii even when exposed to DFMO. Collectively, these results support the hypothesis that P. carinii is unable to regulate polyamine catabolism.     

Pneumocystis carinii infection in a pediatric tuberculosis hospital

An outbreak of pneumocytosis in a children's tuberculosis hospital was analyzed. The infection was characterized by few signs and favourable progress. Antibiotic therapy failed. To eliminate the outbreak of pneumocystosis in the hospital it was necessary to detect all the children with pneumocystosis and carriers of pneumocysts among the patients and medical staff, to use furazolidone for etiotropic treatment of the patients with pneumocystosis and to perform one-stage sanation of the carriers with antiparasitic agents.     

Cytology of extrapulmonary Pneumocystis carinii infection in the acquired immunodeficiency syndrome.

Rare cases of extrapulmonary Pneumocystis carinii (EPPC) have been seen in patients with acquired immunodeficiency syndrome (AIDS). We report seven such diagnoses of nonpulmonary P carinii (PC) from four AIDS patients between 1986 and 1989. The specimens included fine needle aspirate of liver, spleen, periarticular tissue and pleura as well as ankle fluid, pleural fluid and ascites. In some, but not all, cases the patients had concurrent or previous episodes of PC pneumonia. In all cases the typical granular, eosinophilic aggregates of PC cysts were noted on routine Papanicolaou staining, leading to the definitive detection of PC cysts with Grocott silver stain. In most cases, evidence for granulomalike and neovascularized tissue reaction was present in cytologic material. One specimen demonstrated concurrent acid fast bacilli. In the setting of AIDS, cytology of effusions and masses should include an evaluation for EPPC.     

Glucan synthesis in Pneumocystis carinii.

Rat-derived Pneumocystis carinii lysed with sodium deoxycholate catalysed the incorporation of uridine diphosphoglucose into an insoluble polymer. This enzyme activity was present in both the pellet and the supernatant when the P. carinii preparations were centrifuged. The polymer whose production was catalysed by the supernatant was examined by mass spectrometry and found to be an alpha 1----4 glucan, which is either unbranched or has relatively few branches. Polymer formation was completely inhibited by the addition of alpha amyloglucohydrolase to the supernatant. Polymer formation in the pellet of deoxycholate P. carinii preparations, unlike that in the supernatant, was partially resistant to alpha amyloglucohydrolase. The soluble glucan synthase activity in the supernatant was stable for more than 30 h at room temperature and was approximately 50 times more active on a cell-to-cell basis than the supernatant from deoxycholate preparations of the yeast Saccharomyces cerevisae.     

Pneumocystis carinii infection causes lung lesions historically attributed to rat respiratory virus

Idiopathic lung lesions characterized by dense perivascular cuffs of lymphocytes and a lymphohistiocytic interstitial pneumonia have been noted in research rats since the 1990s. Although the etiology of this disease has remained elusive, a putative viral etiology was suspected and the term 'rat respiratory virus' (RRV) has been used in reference to this disease agent. The purpose of this study was to determine whether Pneumocystis carinii infection in immunocompetent rats can cause idiopathic lung lesions previously attributed to RRV. In archived paraffin-embedded lungs (n = 43), a significant association was seen between idiopathic lung lesions and Pneumocystis DNA detected by PCR. In experimental studies, lung lesions of RRV developed in 9 of 10 CD rats 5 wk after intratracheal inoculation with P. carinii. No lung lesions developed in CD rats (n = 10) dosed with a 0.22-μm filtrate of the P. carinii inoculum, thus ruling out viral etiologies, or in sham-inoculated rats (n = 6). Moreover, 13 of 16 CD rats cohoused with immunosuppressed rats inoculated with P. carinii developed characteristic lung lesions from 3 to 7 wk after cohousing, whereas no lesions developed in rats cohoused with immunosuppressed sham-inoculated rats (n = 7). Both experimental infection studies revealed a statistically significant association between lung lesion development and exposure to P. carinii. These data strongly support the conclusion that P. carinii infection in rats causes lung lesions that previously have been attributed to RRV.     

An improved rat model of Pneumocystis carinii pneumonia: induced infections in Pneumocystis-free animals.

An immunosuppressed rat model of Pneumocystis carinii pneumonia (PCP) is described that results in a predictable course of disease development which includes moderate P. carinii (Pc) infections in 2 to 3 weeks, heavy infections in 4 to 5 wk, and a high percentage of mortality due to PCP in 6 wk. The model also provides uninfected, immunosuppressed contemporary controls, an experimental compartment that is needed to correctly interpret results obtained from many different studies. Non-invasive intratracheal inoculation of cryopreserved parasites into Pc- and virus-free rats immunosuppressed by weekly injections of methylprednisolone are key features of the model that result in the development of consistent heavy Pc infections and very few secondary infections by bacteria and fungi. This model is useful for (1) maintaining isolates or strains of Pc over time, (2) producing large numbers of parasites for laboratory studies, and (3) evaluating the anti-Pc activity of experimental compounds and approved drugs.