Early acquisition of Pneumocystis carinii in neonatal rats as evidenced by PCR and oral swabs

The complete life cycle of Pneumocystis carinii has not been defined, but accumulating evidence suggests that the mammalian host may acquire this organism early in life. In the present study, the initial time of P. carinii acquisition was determined in rats by amplification of P. carinii DNA in oral swabs from seven sets of pups and dams and from fetal tissue obtained by cesarean section of three gravid female rats. DNA extracted from all samples was amplified by using PCR primers directed to the P. carinii mitochondrial large subunit rRNA. Amplicons were produced from 80% (28 of 35) of pups within 2 h after birth; from 97% (34 of 35) after 24 h, and in all of the serially sampled pups by 48 h. No P. carinii amplicons were produced from 48 fetuses or their placentae taken by cesarean section. Thus, P. carinii is acquired almost immediately after birth, and placental transmission occurs rarely, if ever, in rats.

Pneumocystis carinii f. sp. hominis is not infectious for SCID mice

The infectious power of Pneumocystis carinii f. sp. hominis was explored by inoculating SCID mice intranasally with either P. carinii f. sp. hominis or P. carinii f. sp. muris isolates. Only mice inoculated with mouse parasites developed Pneumocystis pneumonia, as assessed by microscopy and PCR. These results suggest that humans do not contract pneumocystosis from animals.

Pneumocystis carinii

Pneumocystis carinii is an atypical fungus that causes pneumonia in immunocompromised individuals. P. carinii comprises a heterogeneous group of organisms that have been isolated from a wide range of mammalian host species. P. carinii infection is host species specific, the P. carinii organisms that infect humans have only been found in humans. This review discusses the application of molecular techniques to the study of the biology and epidemiology of P. carinii infection. It addresses the use of DNA amplification for the detection and diagnosis of P. carinii pneumonia. Studies investigating the reservoir of infectious P. carinii organisms, the routes of transmission of the infection, and the emergence of drug resistant strains of P. carinii are also discussed.

[Frequency of Pneumocystis carinii pneumonia in HIV-infected patients in Tunisia]

In Tunisia, as in most african countries, Pneumocystis carinii pneumonia (PCP) is considered to be rare in HIV-infected patients. Frequencies of 8.6% and 21% have been reported. We examined 27 broncho-alveolar lavage specimens collected from HIV-infected tunisian individuals with respiratory symptoms over 4 years (1994-1997), by cyto centrifugation, Giemsa and Gomori-Grocott stain. Pneumocystis carinii (P carinii) was present in 9 cases, accounting for 33.3% of all specimens. Investigation of the reasons for the differences between african reports is necessary to establish appropriate therapeutic management. Technical difficulties of direct recognition of P carinii and selection bias may account for differences between african reports. However, differences still remain between the frequencies recorded in Africa and in other parts of the world, and recent advances seems to correlate this with geographical biodiversity of human-derived strains of P carinii and with differences in host ethnic background.

Vitronectin and fibronectin function as glucan binding proteins augmenting macrophage responses to Pneumocystis carinii

beta-glucans represent major structural components of fungal cell walls. We recently reported that Pneumocystis carinii beta-glucans stimulate alveolar macrophages to release proinflammatory cytokines. Macrophage activation by beta-glucan is augmented by serum, implying the presence of circulating factors that interact with beta-glucans and enhance their ability to stimulate macrophages. Using beta-glucan-enriched cell wall fractions from P. carinii and Saccharomyces cerevisiae, two prominent proteins were precipitated from serum and demonstrated to be vitronectin (VN) and fibronectin (FN) by immune analysis. Preincubation of beta-glucan with VN or FN enhanced macrophage activation in response to this cell wall component. Because VN and FN accumulate in the lungs during P. carinii pneumonia, we further investigated hepatic and pulmonary expression of VN and FN messenger RNA during infection. P. carinii pneumonia in rodents is associated with increased hepatic expression of VN and FN as well as increased local expression of FN in the lung. Because interleukin (IL)-6 represents the major regulator of VN and FN expression during inflammatory conditions, we measured macrophage IL-6 release in response to stimulation with P. carinii beta-glucan. Stimulation of macrophages with P. carinii beta-glucan induced significant release of IL-6. Elevated concentrations of IL-6 were noted in the blood of infected animals compared with uninfected control animals. These studies indicate that VN and FN bind to beta-glucan components of P. carinii and augment macrophage inflammatory responses. P. carinii cell wall beta-glucan stimulates secretion of IL-6 by macrophages, thereby enhancing hepatic synthesis of both VN and FN, and lung synthesis of FN during pneumonia.

Pneumocystis infections: the iceberg?

Pneumocystis carinii pneumonia (PCP) is a well-recognized lung disease of immunocompromised patients, but the real impact of Pneumocystis infection in humans remains to be discovered. Pneumocystis represents probably one of the more frequent infectious agents faced by humans. Seroconversion revealed P. carinii primary infection in > 90% of infants and small children, but the infection source and the clinical or pathological changes associated with this first contact with the parasite remain unknown. Pneumocystis organisms are atypical microfungi able to attach specifically to type-I alveolar epithelial cells, and to proliferate, provoking severe pneumonitis. A deep impairment of cell-mediated immunity associated with changes in pulmonary surfactant make it possible for Pneumocystis to grow within the host. Alveolar type-II cell hypertrophy, macrophagic infiltrate and intra-alveolar foamy eosinophilic material are the most typical changes. CD4+ T-lymphocytes and interferon play a major role in host defense against P. carinii. Alveolar macrophages phagocytose P. carinii via the macrophage-mannose receptor and produce reactive free-radicals and nitric oxide under Pneumocystis stimulation. Furthermore, PCP is associated with an early decrease of surfactant phospholipids, increased hydrophilic surfactant protein (SP) levels and decreased hydrophobic SPs. Normal surfactant improves PCP, and consistently, it inhibits the parasite growth. New detection tools have revealed that hospitalized patients can be latently infected with Pneumocystis and that immunocompetent hosts develop transient Pneumocystis infections. Pneumocystis organisms circulate in human populations, being able to infect hosts with diverse susceptibility levels. In fact, airborne Pneumocystis infection can display a large spectrum of clinical presentations and most likely, we recognize at present only the tip of the iceberg.

Immunosuppressed surfactant protein A-deficient mice have increased susceptibility to Pneumocystis carinii infection

Immunosuppressed Swiss Black mice deficient in surfactant protein A (SP-A(-/-)) and wild-type control mice (SP-A(+/+)) were exposed to Pneumocystis carinii by environmental exposure, intratracheal inoculation, and direct exposure to other infected animals. The frequency and intensity of P. carinii infection were significantly greater in the SP-A(-/-) mice by all 3 methods of exposure. P. carinii free of SP-A and alveolar macrophages were isolated from SP-A(-/-) mice and were tested in an in vitro attachment assay. Pretreatment of P. carinii with human SP-A resulted in a significant dose-dependent increase of the adherence of P. carinii to the macrophages. Thus, SP-A plays a role in host defense against P. carinii in vivo, perhaps by functioning as a nonimmune opsonin.

Clinical correlation of variations in the internal transcribed spacer regions of rRNA genes in Pneumocystis carinii f.sp. hominis

OBJECTIVES

To analyse the importance of sequence variations in the internal transcribed spacer (ITS) regions 1 and 2 of the nuclear rRNA operon in AIDS patients with Pneumocystis carinii pneumonia (PCP).

DESIGN AND METHODS

ITS 1 and 2 genotypes were determined in 162 bronchoalveolar lavage samples from 130 patients participating in a prospective cohort study of PCP.

RESULTS

A total of 49 different ITS genotypes were detected. ITS genotype was not associated with the clinical severity or outcome of PCP. In 37 of 162 (23%) samples infection with two or more genotypes was observed. A genotype switch was detected in six of 10 patients (60%) with recurrent episodes of PCP. However, genotype changes were also seen in 10 of 19 patients (53%) who had repeated bronchoscopies within the same episode of PCP. The same ITS type was observed twice in 13 (46%) of the 28 patients with repeat bronchoscopies during single or recurrent episodes of pneumonia, but in only 14 of 81 (17%) randomly selected pairs (P < 0.01).

CONCLUSION

Although the detection of ITS genotypes is not a random event, changes in genotype can be detected in a single episode of disease, with 23% of PCP patients being infected with more than one P. carinii genotype, thus complicating the use of this locus as a genetic marker to separate new infection from the reactivation of latent infection. ITS genotypes are not associated with the clinical severity of PCP.

A rat model for combined Trypanosoma cruzi and Pneumocystis carinii infection

Dexamethasone treated rats inoculated with Trypanosoma cruzi developed acute parasitemia. In addition, these animals concomitantly developed severe Pneumocystis carinii pneumonia (PCP) and died after 4 weeks of immunosuppression (100%). However, immunocompetent (untreated) rats inoculated with T. cruzi did not acquire P. carinii and recovered from T. cruzi infection. Rats immunosuppressed, but not inoculated with T. cruzi, developed only PCP and died 5-6 weeks later (93%). In contrast, immunocompetent or immunocompromised IRC mice infected with T. cruzi all died of acute parasitemia in only 8-12 days with no detectable PCP infection. In conclusion, rats immunosuppressed and T. cruzi inoculated can serve as a MOPPS model for a single drug evaluation. In addition, T. cruzi infection independently does not provoke P. carinii pneumonia in this model. Finally, patients with Chagas' disease treated with corticosteroids may be at risk for PCP and should be considered for chemoprophylaxis.

Transmission of Pneumocystis carinii disease from immunocompetent contacts of infected hosts to susceptible hosts

Pneumocystis carinii organisms constitute a large group of heterogeneous atypical microscopic fungi that are able to infect immunocompromised mammals by an airborne route and to proliferate in their lungs, inducing Pneumocystis carinii pneumonia. This pneumonia remains a crucial epidemiological challenge, since neither the source of Pneumocystis carinii infection in humans nor the process by which humans become infected has been clearly established. Polymerase chain reaction (PCR) assays have shown that profoundly immunosuppressed patients without pneumocystosis can be subclinically infected with Pneumocystis. Other PCR-based studies have suggested that healthy immunocompetent hosts are not latent carriers of the parasite. However, recent reports have indicated that Pneumocystis carinii can persist for limited periods in the lungs of convalescent rats after recovery from corticosteroid-induced pneumocystosis, and also that immunocompetent mammals can be transiently parasitized by Pneumocystis carinii after close contact with hosts with Pneumocystis carinii pneumonia. Can transiently parasitized hosts be a source of infection for immunosuppressed hosts? In order to investigate this important clinical question, the ability of immunocompetent BALB/c mice, which were carrying subclinical levels of Pneumocystis carinii, to transmit the infection by the airborne route to highly susceptible, uninfected mice with severe combined immunodeficiency was studied. The results indicated that the immunocompetent mice, transiently parasitized by Pneumocystis carinii organisms after close contact with Pneumocystis carinii-infected mice, were able to transmit the infection to Pneumocystis carinii-free mice with severe combined immunodeficiency.

Pneumocystis carinii enhances soluble mannose receptor production by macrophages

Phagocytosis of extracellular organisms in the alveolar spaces of the lungs represents the first-line of host defense against pulmonary pathogens. Disruption of this process is likely to interfere with the generation of appropriate specific immune responses, and lead to a delayed or inefficient clearance of the pathogen. Pneumocystis carinii, an opportunistic pathogen in immunodeficient individuals, is cleared from the lung by alveolar macrophages. In the absence of specific anti-Pneumocystis antibodies, phagocytosis is dependent on the non-opsonic macrophage mannose receptor (MR). Recent studies have demonstrated that alveolar macrophage MR activity is downregulated in individuals infected with HIV, and that functional MR is shed from the macrophage cell surface. Here we report that P. carinii enhances the formation of soluble MR by macrophages in vitro. Soluble MR was detected in cell-free alveolar fluid from humans infected with HIV and/or P. carinii, but not in alveolar fluid from healthy controls. Soluble MR was found in association with extracellular clumps of P. carinii in the lungs of mice with P. carinii pneumonia, and was associated with P. carinii organisms purified from these mice. When purified P. carinii organisms were incubated with soluble MR-containing supernatants, they were phagocytosed less readily by alveolar macrophages than were control organisms. Our results suggest that P. carinii organisms enhance the shedding of MR from the surface of alveolar macrophages, and that the resultant soluble MR binds to intra-alveolar organisms, thereby interfering with their non-opsonic uptake via the macrophage cell surface MR.

A soluble mannose receptor immunoadhesin enhances phagocytosis of Pneumocystis carinii by human polymorphonuclear leukocytes in vitro

Pneumocystis carinii is an opportunistic pathogen that causes pneumonia in immunocompromised hosts. In the normal host, P. carinii is susceptible to an array of first line host defense mechanisms that are operative in the lung. Alveolar macrophages play a central role in the clearance of inhaled organisms. The macrophage mannose receptor (MR) appears to be sufficient for P. carinii phagocytosis. In individuals infected with the human immunodeficiency virus, MR expression on alveolar macrophages and P. carinii phagocytosis are decreased, however, Fc-receptor mediated phagocytosis remains intact. In this study, we demonstrate that a recombinant soluble MR immunoadhesin, consisting of the essential carbohydrate binding MR ectodomain and the Fc-region of human immunoglobulin (Ig)G1, binds P. carinii and leads to an 8.2-fold increased uptake of P. carinii by phagocytic cells. Our results suggest that the soluble MR immunoadhesin may have therapeutic potential in the treatment of P. carinii infections.

Common variable immunodeficiency in miniature dachshunds affected with Pneumonocystis carinii pneumonia

Seven miniature dachshunds, all under the age of 1 year, were presented with polypnea, tachypnea, and exercise intolerance as a result of Pneumocystis carinii pneumonia, which was diagnosed on transtracheal aspirate cytology. In all of the dogs, historical and clinical signs were suggestive of immune incompetence. Immunological studies undertaken were leukogram parameters, serum immunoglobulin fraction quantification, lymphocyte transformation assay. CD3 and CD79a lymphocyte markers on lymphoid tissue, and anti-canine immunoglobulin G immunoperoxidase staining. The immunological studies showed hypogammaglobulinemia, deficiency of serum immunoglobulins A, G, and M, decreased lymphocyte transformation response to phytohemagglutinin and pokeweed mitogens and absence of B lymphocytes with presence of T lymphocytes in the lymphoid tissue stained with CD3 and CD79a lymphocyte markers. The preceding findings suggest that P. carinii pneumonia occurring in the miniature dachshund is a result of both a T- and B-cell deficiency. This presentation is not the classic primary severe combined immunodeficiency syndrome but rather combined variable immunodeficiency, which has been well documented in humans but never in the dog.

A case of interstitial pneumonia associated with Pneumocystis carinii in a foal

Subacute interstitial pneumonia with diffuse alveolar damage, marked macrophage infiltration, and intracellular Pneumocystis carinii cysts is described in a 3-month-old Swiss warmblood foal. Clinically, the disease was characterized by sudden onset of respiratory distress with fatal outcome. Based on serum immunoglobulin G (IgG), IgA, and IgM values, no humoral immunosuppression was detected. Spleen, thymus, and bronchial lymph nodes did not reveal lymphoid depletion, as assessed by immunohistochemical staining of CD-3-positive cells. Immunopathogenesis of pulmonary infections with intracellular agents in foals is discussed.

Nodular Pneumocystis carinii pneumonia in SIV-infected macaques

Pneumocystis carinii (PC) pneumonia is a frequent manifestation of the acquired immunodeficiency syndrome (AIDS) in humans and macaques. An unusual nodular type of PC pneumonia was observed in two simian immunodeficiency virus (SIV)-inoculated rhesus macaques (Macaca mulatta). These animals developed clinical signs of simian AIDS, including anorexia, weight loss, dyspnea, and collapse. Grossly, both animals had multifocal tan-white nodules 1-10 mm in diameter scattered throughout the lungs. One animal had similar nodules involving the diaphragm and thoracic wall. The lungs were characterized by severe PC pneumonia with numerous large nodules consisting of foamy material that compressed adjacent tissue. The nodules had central areas of necrosis and lysis of alveolar septa. Varying degrees of necrotizing vasculitis were observed in areas of nodular PC pneumonia. The presence of PC in intra-alveolar spaces and nodular lesions was confirmed by immunohistochemistry. No evidence of other agents, including viral inclusions, bacteria, fungi, and lung mites, was detected. The animal with the most severe nodular PC pneumonia had vascular involvement with extrapulmonary spread to the diaphragm, thoracic wall, and regional lymph nodes. This unusual type of nodular PC pneumonia has been rarely seen in human AIDS patients.