Susceptibility of various animals to Pneumocystis carinii infection.

Pneumocystis carinii (Pc) is an important opportunistic pathogen of immune compromised hosts, and is known to infect various animals. The present study observed the infection status of 6 mammals and 3 strains of albino rats with Pc after suppression of their immunity. Methyl-prednisolone was injected once a week and tetracycline was supplied with water for 5 to 21 weeks. Hamsters, guinea pigs, rabbits, dogs, cats and pigs were negative by impression smear, and only the rats were found infected by Pc. All of the three strains of rats, Sprague-Dawley(SD), Wistar(W) and Fisher(F), were infected by Pc but W rats showed heavier degree of infection in earlier period than F or SD rats. The present findings suggest that W rat is the best among the animals used in the present study for production of Pc.     

A survey of Pneumocystis carinii infection in research mouse colonies in Japan.

To determine the frequency of Pneumocystis carinii infection in mouse colonies maintained for biomedical research in medical colleges or medical faculties in universities in Japan, 409 nu/nu mice were sent to 43 animal facilities from a P. carinii-free colony. The animals were housed for 6 months in groups of 3 to 10 animals per room, and examined for the presence of parasites and infection. Colonies in 10 (24.4%) of 41 facilities were positive for the infection. Of 383 animals in 69 rooms, the organism was detected in 66 (17.2%) animals in 13 (18.8%) rooms. The difference in the proportion of rooms where mice were positive for P. carinii is clearly seen among these three groups; SPF mouse rooms (4 of 38 rooms, 10.5%), SPF mouse rooms with breeding units (5 of 25 rooms, 20.0%) and conventional mouse rooms (4 of 6 rooms, 66.7%). The survey indicates that strict housing arrangements and husbandry techniques are necessary to keep SPF mice free from P. carinii infection.     

Inoculated mouse model of Pneumocystis carinii pneumonia.

A transtracheally inoculated mouse model of Pneumocystis carinii has been developed using BALB/c mice, a widely available strain free of latent P. carinii infection. The mean infectivity score of untreated inoculated mice was 4.1 compared to the mean infectivity score of 0.1 for trimethoprim/sulfamethoxazole (50/250 mg/kg) treated inoculated mice, approximately a four-log difference. An inoculated mouse model of P. carinii infection provides both a source of organisms from a different host and an animal model for study of drugs for therapy and prophylaxis which is less costly than rats and which requires less drug than required for rats.     

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.     

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.     

Interstitial pneumonia in immunocompetent laboratory rats caused by natural infection with Pneumocystis carinii

Pneumocystis (P.) carinii is known to cause fatal pneumonia in immunocompromised rats. Cases of P. carinii interstitial pneumonia in immunocompetent rats have been shown histologically to present with perivascular lymphoid cuffs, which have previously been attributed to rat respiratory virus. This study aims to determine the prevalence and pathological characteristics of P. carinii in immunocompetent laboratory rats in experimental facilities in Japan. An epidemiological survey for this agent was performed using PCR to assess 1,981 immunocompetent rats from 594 facilities in Japan. We observed that 6 of the 1,981 rats (0.30%) from 4 out of 594 facilities (0.67%) were positive for P. carinii without infection of other known pathogens. Gross pulmonary lesions were found in 4 of the 6 affected rats. The lungs of these rats contained scattered dark red/gray foci. Histopathologically, the lungs exhibited interstitial pneumonia with lymphoid perivascular cuffs: Pneumocystis cysts were observed using Grocott’s methenamine silver stain. To our knowledge, this report is the first to reveal the prevalence of natural P. carinii infection in immunocompetent laboratory rats in Japan.     

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 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.     

Update on the epidemiology and transmission of Pneumocystis carinii

Although Pneumocystis carinii pneumonia is one of the leading causes of morbidity and mortality among patients with the acquired immunodeficiency syndrome, many questions about its epidemiology and transmission remain unanswered. Whereas traditional theory postulates that the disease results from reactivation of latent infection, recent data suggest that active acquisition of infection, either through environmental exposure or person-to-person transmission, may occur. This review summarizes the current state of knowledge about the epidemiology and transmission of P. carinii and reports on evolving techniques that may improve our understanding of this organism in the future.     

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.     

Delayed-type hypersensitivity response in mice to Pneumocystis carinii.

Resistance to Pneumocystis carinii infection appears to be mediated by T lymphocytes but the mechanism and subsets of T cells involved are poorly understood. We used the BALB/c mouse model to study the delayed-type hypersensitivity (DTH) response to rat P. carinii. Mice were sensitized to P. carinii for seven days and then challenged with P. carinii antigens in the right rear footpads and normal rat lung antigens in the left rear footpads. A typical DTH response was observed in the right footpads as evidenced by significant swelling and substantial mononuclear cell infiltration at 24-h post-challenge. The DTH response could be transferred to naive syngeneic mice by adoptively transferring spleen cells from P. carinii-sensitized mice. In addition, by using anti-thy-1, anti-mouse Ig, anti-L3T4 and anti-Lyt-2.2 monoclonal antibodies in in vitro cytolysis experiments, we were able to demonstrate that the DTH response was dependent upon T lymphocytes. The response appeared to require cooperation between both L3T4+ and Lyt 2+ subsets of T lymphocytes.     

Study on placental transmission of Pneumocystis carinii in mice using immunodeficient SCID mice as a new animal model.

Placental transmission of Pneumocystis carinii in mice was examined in 39 animals obtained by caesarean section from 17 pregnant SCID females experimentally infected with P. carinii. When examined with toluidine blue O, DAPI and immunofluorescent antibody stains, P. carinii was detected in the lungs of infected mothers but not in the lungs of caesarean section-derived neonates even after the neonates were treated with dexamethasone for 8 weeks. However, 13 neonates born to five infected females developed P. carinii pneumonia. These results indicate that P. carinii cannot be transmitted transplacentally in mice.     

Detection and quantification of Pneumocystis carinii using a sandwich ELISA.

Antigenic sites on Pneumocystis carinii, the basis for organism enumeration by an enzyme-linked immunosorbent assay (ELISA) were adversely affected by incubation in detergents. However, stronger detergent concentrations were needed to eliminate high levels of non-specific background. Good P. carinii quantification was obtained with low non-specific background when the detergent was used only in the washing steps and not in cell suspension solutions. Formalin fixation of the cells resulted in good ELISA quantification of organism numbers with low non-specific background. No adverse effects were observed using a detergent on fixed cells. Although the system's range of accuracy needs to be expanded, a reduction in the number of organisms in response to the effects of pentamidine in vitro could be demonstrated by ELISA.     

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.