Detection of surface carbohydrates on Pneumocystis carinii by fluorescein-conjugated lectins

Additional C-type lectin receptors mediate interactions with Pneumocystis organisms and major surface glycoprotein

Introduction. Pathogen-associated molecular patterns' (PAMPs) are microbial signatures that are recognized by host myeloid C-type lectin receptors (CLRs). These CLRs interact with micro-organisms via their carbohydrate recognition domains (CRDs) and engage signalling pathways within the cell resulting in pro-inflammatory and microbicidal responses.Gap statement. In this article, we extend our laboratory study of additional CLRs that recognize fungal ligands against Pneumocystis murina and Pneumocystis carinii and their purified major surface glycoproteins (Msgs).Aim. To study the potential of newly synthesized hFc-CLR fusions on binding to Pneumocystis and its Msg.Methods. A library of new synthesized hFc-CLR fusions was screened against Pneumocystis murina and Pneumocystis carinii organisms and their purified major surface glycoproteins (Msgs) found on the respective fungi via modified ELISA. Immunofluorescence assay (IFA) was implemented and quantified to verify results. mRNA expression analysis by quantitative PCR (q-PCR) was employed to detect respective CLRs found to bind fungal organisms in the ELISA and determine their expression levels in the mouse immunosuppressed Pneumocystis pneumonia (PCP) model.Results. We detected a number of the CLR hFc-fusions displayed significant binding with P. murina and P. carinii organisms, and similarly to their respective Msgs. Significant organism and Msg binding was observed for CLR members C-type lectin domain family 12 member A (CLEC12A), Langerin, macrophage galactose-type lectin-1 (MGL-1), and specific intracellular adhesion molecule-3 grabbing non-integrin homologue-related 3 (SIGNR3). Immunofluorescence assay (IFA) with the respective CLR hFc-fusions against whole P. murina life forms corroborated these findings. Lastly, we surveyed the mRNA expression profiles of the respective CLRs tested above in the mouse immunosuppressed Pneumocystis pneumonia (PCP) model and determined that macrophage galactose type C-type lectin (Mgl-1), implicated in recognizing terminal N-acetylgalactosamine (GalNAc) found in the glycoproteins of microbial pathogens was significantly up-regulated during infection.Conclusion. The data herein add to the growing list of CLRs recognizing Pneumocystis and provide insights for further study of organism/host immune cell interactions.

Pneumocystis Carinii Pneumonia in Adult Non-HIV Disorders

Pneumocystis carinii pneumonia (PCP) remains a serious infection in the immunocompromised host (in the absence of HIV infection) and presents significant management and diagnostic challenges to ICU physicians. Non-HIV PCP is generally abrupt in onset, and follows a fulminate course with high rates of hospitalization, ICT admission, respiratory failure, and requirement for intubation. Mortality is generally high, especially if mechanical ventilation is required. Non-invasive ventilatory support may be considered, although the rapid progression to respiratory failure often necessitates intubation at the time of presentation. Bronchoscopy is often required to establish the diagnosis, and empirical antimicrobial treatment specifically targeted to P. carinii should be initiated while awaiting confirmation. Adjunctive corticosteroids may accelerate recovery, although their use has not yet been established in non-HIV PCP. For the ICU physicians to diagnose PCP, the non-specific presentation of an acute febrile illness and respiratory distress with diffuse pulmonary infiltrates requires a high clinical index of suspician, familiarity with clinical conditions associated with increased risk for PCP, and a low threshold for bronchoscopy to establish the diagnosis.

Pneumocystis jiroveci Pneumonia

Pneumocystis pneumonia (PCP) is one of the most common pulmonary infections in persons with impaired cell-mediated immunity, and particularly those infected with human immunodeficiency virus (HIV).1–7 Pneumocystis was first described in the lungs of guinea pigs, during experiments on American trypanosomiasis by Carlos Chagas8 in 1909 and by Antonio Carinii9 in 1910. Both considered the cysts of Pneumocystis as part of the trypanosome’s life cycle. Shortly afterward the Delanoes10 found identical forms in the lungs of rats that had not been infected with trypanosomes and recognized the organism as a separate species. The name Pneumocystis carinii, was given to this organism as a generic name (Greek:pneumon, “lung”; kystis, “cyst”), honoring Carinii.11

Basic biology of Pneumocystis carinii: a mini review

Basic aspects of cell biology of Pneumocystis carinii are reviewed with major emphasis on its life cycle and the structural organization of the trophozoites and cyst forms. Initially considered as a protozoan it is now established that Pneumocystis belongs to the Fungi Kingdom. Its life cycle includes two basic forms: (a) trophozoites, which are haploid cells that divide by binary fission and may conjugate with each other forming an early procyst and (b) cysts where division takes place through a meiotic process with the formation of eight nuclei followed by cytoplasmic delimitation and formation of intracystic bodies which are subsequently released and transformed into trophozoites. Basic aspects of the structure of the two developmental stages of P. carinii are reviewed.

Pneumocystis carinii: what is it, exactly?

The identity of Pneumocystis carinii has been uncertain for many years. Until recently, it was widely regarded to be a protozoan because it does not grow in culture and is not susceptible to antifungal drugs. Although these and a number of other phenotypic characteristics of P. carinii differ from those of typical fungi, analysis of DNA sequences has shown that P. carinii is a member of the fungal lineage of eukaryotes. However, a close phylogenetic relative of P. carinii has not yet been found. Analysis of gene sequences has also revealed that P. carinii is not a single entity but that the genus Pneumocystis contains a complex group of organisms. P. carinii organisms from one host species do not grow when introduced into another host species, and P. carinii isolates from different host species are more genetically divergent from one another than might be expected for members of the same species. Genetic variation of a lesser degree also occurs among P. carinii organisms from the same host species, suggesting that it may be possible to identify strains and to conduct transmission and epidemiological studies. Results of early studies exploiting genetic variation among P. carinii isolates from patients have suggested that recurrent P. carinii pneumonia may not always be caused by reactivation of latent organisms, as is commonly believed. However, other features of P. carinii suggest that this microbe has established a long-term relationship with its host. A striking new development in this regard is the discovery of a genetic system that is designed to allow variation in the structure of a major antigen on the surface of P. carinii.

Pathogenesis and host response in Pneumocystis carinii pneumonia

Pneumocystis carinii (PC) pneumonia is recognized as the leading cause of opportunistic pulmonary infections in immunocompromised hosts during the past decade. Although much remains unknown about pathogenesis and host response in PC, recent years, studies of PC have provided us with an increasing base of knowledge about this organism and its relationship to the host. These studies have led to a better understanding of mechanisms of PC attachment and injury to host cells. New information about the interaction of PC with pulmonary surfactant provides insight about the pathophysiology of PC pneumonia. The interplay of the organism, host inflammatory cells, release of cytokines, generation of toxic metabolites, and involvement of both cellular and humoral immunity is complex, but understanding the pathogenesis of PC pneumonia is necessary in order to develop new therapies for this disorder.

High osmotic pressure for Pneumocystis carinii London Resin White embedding enables fine immunocytochemistry studies: I. Golgi complex and cell-wall synthesis

A method for embedding Pneumocystis carinii in hydrophilic resin (London Resin White) has been developed for immunocytochemistry studies. Using high osmotic pressure (about 850 mosmol) from fixation to embedding, this method improved the preservation of the fine structure as well as the antigenicity of rabbit- and SCID mouse-derived P. carinii. Cytochemistry studies were performed using colloidal gold-conjugated lectins (concanavalin A, glycine max, Ulex europaeus) that reacted with the cytoplasmic components (endoplasmic reticulum, Golgi vesicles). Colloidal gold-conjugated streptavidin was also tested and was found to be reactive with the parasite cell wall and cytoplasmic components, which precludes its indiscriminate use in P. carinii immunocytochemistry studies.

Three-dimensional reconstruction of rabbit-derived Pneumocystis carinii from serial-thin sections. II: Intermediate precyst

Three-dimensional reconstruction of a binucleate intermediate precyst of Pneumocystis carinii was performed from serial-thin sections using the CATIA (Conception Assistée Tridimensionnelle Inter Active) Dassault system program. The presence of a mitochondrion, complex well-developed endoplasmic structures, and numerous Golgi vesicles was established. A better understanding of the ultrastructure of rabbit-derived P. carinii stages made it possible to formulate hypotheses on the evolution and physiology of the endomembrane system. Thus, the presence of the well-developed endoplasmic saccular structure and more than 230 Golgi vesicles in its vicinity might be implicated in the differentiation of the parasite surface structures and might also be related to nuclear division and individualization of intracystic bodies.

Purification and characterization of a major human Pneumocystis carinii surface antigen

Previous studies of Pneumocystis carinii have identified the major surface antigen of rat and human isolates as proteins of 116,000 and 95,000 mol wt, respectively, that are antigenically not identical. In this study both rat and human P. carinii proteins were purified by solubilization with zymolyase followed by molecular sieve and ion exchange chromatography. The native proteins had an apparent mol wt of 290,000 or greater, based on molecular sieve studies as well as cross-linking studies. Both proteins were glycoproteins; treatment with endoglycosidase H resulted in a 9% decrease in mol wt. The carbohydrate composition of the rat P. carinii glycoprotein was distinct from the human isolate; glucose, mannose, galactose, and glucosamine occurred in approximately equimolar ratios in the human P. carinii protein, whereas glucose and mannose were the predominant sugars of the rat P. carinii protein. To evaluate humoral immune responses to the human P. carinii protein, an enzyme-linked immunosorbent assay using purified protein was developed. Some, but not all, patients who subsequently developed P. carinii pneumonia demonstrated a serum antibody response to the surface antigen. Nearly all subjects without a history of P. carinii pneumonia had no detectable antibodies. Purified P. carinii proteins will greatly facilitate the investigation of host-P. carinii interactions.

Analysis of Pneumocystis carinii cyst wall. II. Sugar composition

Pneumocystis carinii cysts are capable of resisting host defenses and antimicrobial drugs and are therefore thought to be responsible for relapses of P. carinii pneumonia in AIDS and other immunocompromised patients. The interaction of P. carinii with its host, and other P. carinii, might be mediated by molecules which form the outer surfaces of this organism. Carbohydrates are known to play many roles in cell-cell adhesion, and have been detected on the surface of P. carinii by lectin labeling experiments. In this study P. carinii cyst wall material was obtained from Zymolyase treatment. Alditol acetate derivatives of neutral and amino sugars or trimethylsilyl derivatives of methyl glycosides were prepared from the monosaccharides released from the sample by acid hydrolysis. Analyses were done by a combination of gas chromatography and mass spectrometry. Glucose was found to be the major sugar constituent. Mannose and galactose were present in equal ratios. A lesser amount of N-acetyl-D-glucosamine, and trace amounts of ribose and sialic acid were present in the cyst wall samples analyzed. These sugars may mediate P. carinii-host interaction and play an important protective role by creating a permeability barrier around the cyst.

Endogenous carbohydrate-binding proteins in Pneumocystis carinii

By using biotinylated neoglycoproteins, the in situ occurrence of endogenous carbohydrate-binding proteins (lectins) in Pneumocystis carinii has been glycohistochemically demonstrated in lung tissue specimens from acquired immunodeficiency syndrome patients with P. carinii pneumonia. While the parasite possessed only a weak to moderate density of receptors for L-fucose and N-acetylated amino sugars, a strong specific binding of beta-D-galactoside and D-mannoside neoglycoproteins was observed on the cyst surface and within intracystic bodies. It is suggested that these endogenous lectins may be involved in the adhesion of P. carinii to the target.

Lectins and their application to clinical microbiology

Lectins are generally associated with plant or animal components, selectively bind carbohydrates, and interact with procaryotic and eucaryotic cells. Lectins have various specificities that are associated with their ability to interact with acetylaminocarbohydrates, aminocarbohydrates, sialic acids, hexoses, pentoses, and as other carbohydrates. Microbial surfaces generally contain many of the sugar residues that react with lectins. Lectins are presently used in the clinical laboratory to type blood cells and are used in a wide spectrum of applications, including, in part, as carriers of chemotherapeutic agents, as mitogens, for fractionation of animal cells, and for investigations of cellular surfaces. Numerous studies have shown that lectins can be used to identify rapidly certain microorganisms isolated from a clinical specimen or directly in a clinical specimen. Lectins have been demonstrated to be important diagnostic reagents in the major realms of clinical microbiology. Thus, they have been applied in bacteriology, mycology, mycobacteriology, and virology for the identification and/or differentiation of various microorganisms. Lectins have been used successfully as epidemiologic as well as taxonomic markers of specific microorganisms. Lectins provide the clinical microbiologist with cost-effective and potential diagnostic reagents. This review describes the applications of lectins in clinical microbiology.

Pneumocystis carinii: surface reactive carbohydrates detected by lectin probes

Pneumocystis carinii obtained from rat lungs (RLH) and in vitro culture (RTC) were reacted with a panel of 14 fluorescein isothiocyanate conjugated lectins. Percentage fluorescence and fluorescent intensity were determined for both trophic and cyst forms. All RLH and RTC derived organisms bound strongly concanavalin A (Con A), and wheat germ agglutinin (WGA). However, differences in soybean agglutinin (SBA) binding between RLH and RTC organisms was observed. Different subsets of the organism bound lectins from Griffonia simplicifolia I, Maclura pomifera, and Bauhinia purpurea, indicating heterogeneity in the surface carbohydrates within each of the RLH and RTC populations. Eight lectins reacted very weakly or not at all: Dolichos biflorus, Arachis hypogaea, Griffonia simplicifolia I-beta 4, Solanum tuberosum, Ulex europeus, Griffonia simplicifolia II, Viscum album, and Limax flavus. The results indicate that P. carinii trophic and cyst forms have surface constituents containing mannose, N-acetylglucosamine and N-acetylgalactosamine as the predominant carbohydrates. Molecules resembling sialic acid and beta-galactose are absent or inaccessible. The surface glycoconjugates identified in these studies may play a role in the adherent properties of P. carinii.

Ultrastructural detection of carbohydrates in the pellicle of Pneumocystis carinii

The presence of carbohydrates in the pellicle of Pneumocystis carinii was demonstrated by methenamine silver (MS) and thiocarbohydrazide-silver proteinate (TCH-SP) staining techniques. An intense, positive reaction with MS was observed on both the electron-dense outer layer and the electron-lucent middle layer of the pellicle, whereas in the case of TCH-SP only the outer layer stained well. The middle layer did not stain as intensely with TCH-SP as with MS. This observation indicates that the pellicle of P. carinii contains carbohydrates but that the outer and middle layers differ in carbohydrate composition. The binding sites of concanavalin A (Con A) and Macura pomifera (MPA) lectins were elucidated on the pellicle of P. carinii using colloidal gold as a marker. In a preembedding staining method using Con A and MPA lectins, the adherence of gold particles was observed on the surface of all stages of the parasite. The homogeneous distribution of the gold particles indicates that the outer electron-dense layer contains both Con A- and MPA-specific carbohydrates. In postembedding staining with Con A, the adherence of gold particles was found on both the outer and middle layers, whereas in the case of MPA only the outer layer was labeled with gold particles. These results indicate that the electron-dense outer layer contains a considerable amount of carbohydrates specific for these lectins, whereas the electron-lucent middle layer seems to lack MPA-specific carbohydrates.