Use of immunoblotting to detect Aspergillus fumigatus antigen in sera and urines of rats with experimental invasive aspergillosis

Rodent Models of Invasive Aspergillosis due to Aspergillus fumigatus: Still a Long Path toward Standardization

Invasive aspergillosis has been studied in laboratory by the means of plethora of distinct animal models. They were developed to address pathophysiology, therapy, diagnosis, or miscellaneous other concerns associated. However, there are great discrepancies regarding all the experimental variables of animal models, and a thorough focus on them is needed. This systematic review completed a comprehensive bibliographic analysis specifically-based on the technical features of rodent models infected with Aspergillus fumigatus. Out the 800 articles reviewed, it was shown that mice remained the preferred model (85.8% of the referenced reports), above rats (10.8%), and guinea pigs (3.8%). Three quarters of the models involved immunocompromised status, mainly by steroids (44.4%) and/or alkylating drugs (42.9%), but only 27.7% were reported to receive antibiotic prophylaxis to prevent from bacterial infection. Injection of spores (30.0%) and inhalation/deposition into respiratory airways (66.9%) were the most used routes for experimental inoculation. Overall, more than 230 distinct A. fumigatus strains were used in models. Of all the published studies, 18.4% did not mention usage of any diagnostic tool, like histopathology or mycological culture, to control correct implementation of the disease and to measure outcome. In light of these findings, a consensus discussion should be engaged to establish a minimum standardization, although this may not be consistently suitable for addressing all the specific aspects of invasive aspergillosis.

Elisa based diagnostic test for Aspergillosis

Detection of lgE and lgG antibodies in Aspergillosis is of diagnostic significance. The serological methods, such as agglutination, gel diffusion and counter immuno electrophoresis that are commonly used in the laboratories for diagnosis of Aspergillus induced infections, are less sensitive and high cross reactivity is often encountered. We carried out work on characterization and identification of diagnostically relevant antigens ofA. fumigatus. Well characterized antigens were used to develop an ELISA with 92% sensitivity and 89% specificity for detection of specific lgE and lgG in the sera of patients of allergic bronchopulmonary aspergillosis (ABPA), aspergilloma and invasive aspergillosis. Subsequently, a sample kit having "ready to use type" of dry reagents (powder/tableted buffers and lyophilized antigen, conjugate and reference sera) was formulated. The kit was validated with sera from patients of ABPA, related allergic disorders, tuberculosis, post-Kochs cases and thalassemic children receiving repeated blood transfusions. The performance of the kit was found to be satisfactory with coded sera.

Immunoproteomics based identification of thioredoxin reductase GliT and novel Aspergillus fumigatus antigens for serologic diagnosis of invasive aspergillosis

Background

There has been a rising incidence of invasive aspergillosis (IA) in critically ill patients, even in the absence of an apparent predisposing immunodeficiency. The diagnosis of IA is difficult because clinical signs are not sensitive and specific, and serum galactomannan has relatively low sensitivity in this group of patients. Therefore, more prompt and accurate disease markers for early diagnosis are needed. To establish disease markers demands a thorough knowledge of fungal antigens which may be detected in the serum or other body fluids of patients. Herein we report novel immunodominant antigens identified from extracellular proteins of Aspergillus fumigatus.

Results

Extracellular proteins of A. fumigatus were separated by two-dimensional electrophoresis (2-DE) and probed with the sera from critically ill patients with proven IA. The immunoreactive protein spots were identified by MALDI-TOF mass spectrometry (MALDI-TOF -MS). Forty spots from 2DE gels were detected and 17 different proteins were identified as immunogenic in humans. Function annotation revealed that most of these proteins were metabolic enzymes involved in carbohydrate, fatty acid, amino acid, and energy metabolism. One of the proteins, thioredoxin reductase GliT (TR), which showed the best immunoactivity, was analyzed further for secretory signals, protein localization, and homology. The results indicated that TR is a secretory protein with a signal sequence exhibiting a high probability for secretion. Furthermore, TR did not match any human proteins, and had low homology with most other fungi. The recombinant TR was recognized by the sera of all proven IA patients with different underlying diseases in this study.

Conclusions

The immunoreactive proteins identified in this study may be helpful for the diagnosis of IA in critically ill patients. Our results indicate that TR and other immunodominant antigens have potential as biomarkers for the serologic diagnosis of invasive aspergillosis.

Analysis of the major proteins secreted by the human opportunistic pathogenAspergillus fumigatusunderin vitroconditions

Although secreted proteins of pathogenic microorganisms often represent potential virulence factors, so far only limited information has been available on the proteins secreted by Aspergillus fumigatus. We therefore analysed supernatant proteins after growth in different media. In serum-free cell culture medium A. fumigatus growth was limited and no protein secretion was detectable, whereas distinct protein patterns were detectable after growth in either aspergillus minimal medium (AMM) or the more complex yeast glucose medium (YG). The three major proteins secreted under these conditions were identified as the ribotoxin mitogillin, a chitosanase and the aspergillopepsin i. Mitogillin and chitosanase were secreted in AMM, whereas aspergillopepsin i was especially prominent after growth in YG. When the AMM cultures reached stationary phase, seven additional major proteins were detectable. Two of them were identified as the chitinase chiB1 and a beta(1-3) endoglucanase. Conditioned medium containing mitogillin and chitosanase did not have a detectable cytotoxic effect on A549 and Vero cells. Using recombinant mitogillin and chitosanase we detected anti-chitosanase and antimitogillin antibodies in sera of patients suffering from invasive aspergillosis or aspergilloma, but not in control sera of healthy individuals. This suggests that chitosanase, like mitogillin, is expressed during infection and might therefore be of diagnostic relevance.

Immunochemical detection of molds: a review

Molds are widely distributed in nature and cause deterioration of foods and feeds. Their mycotoxins can adversely affect human and animal health. Suitable assays for molds, therefore, are required to implement control and regulatory strategies and to develop appropriate feeding regimens for mold-infested feeds. Many different types of mold assays have been used, most of which are not reproducible or accurate. However, the immunoassays, particularly enzyme-linked immunosorbent assays (ELISAs), can be especially useful. Among these, assays that detect the water-soluble extracellular secretions of fungi, the exoantigens, are generally able to detect fungi at the genus or species level, whereas the heat-stable polysaccharides tend to be specific for one or more genus of fungi. Several species and genus (genera)-specific ELISAs have been developed using monoclonal or polyclonal antibodies against exoantigens and heat-stable polysaccharides from a wide range of fungi, including Aspergillus, Penicillium, and Fusarium species. Other assays have been developed that nonspecifically detect mold in food or feed, some using antibodies against a mixture of antigens from different fungi. These assays are highly sensitive, are easy to perform, and provide an index of the amount of mold present in the sample. Further refinement of these assays should facilitate their widespread use by food and feed processors, regulatory agencies, taxonomists, and research scientists.

Aspergillus fumigatus and aspergillosis

Aspergillus fumigatus is one of the most ubiquitous of the airborne saprophytic fungi. Humans and animals constantly inhale numerous conidia of this fungus. The conidia are normally eliminated in the immunocompetent host by innate immune mechanisms, and aspergilloma and allergic bronchopulmonary aspergillosis, uncommon clinical syndromes, are the only infections observed in such hosts. Thus, A. fumigatus was considered for years to be a weak pathogen. With increases in the number of immunosuppressed patients, however, there has been a dramatic increase in severe and usually fatal invasive aspergillosis, now the most common mold infection worldwide. In this review, the focus is on the biology of A. fumigatus and the diseases it causes. Included are discussions of (i) genomic and molecular characterization of the organism, (ii) clinical and laboratory methods available for the diagnosis of aspergillosis in immunocompetent and immunocompromised hosts, (iii) identification of host and fungal factors that play a role in the establishment of the fungus in vivo, and (iv) problems associated with antifungal therapy.

Production of specific monoclonal antibodies to Aspergillus species and their use in immunohistochemical identification of aspergillosis

Two anti-Aspergillus murine monoclonal antibodies (MAbs), designated 164G and 611F, have been produced; both specifically recognize cytoplasmic antigens of A. fumigatus, A. flavus, and A. niger by enzyme-linked immunosorbent assay. The MAbs can identify Aspergillus spp. both in frozen sections by immunofluorescence and in paraffin-embedded clinical specimens by immunofluorescence and immunoperoxidase staining.

The characterization of chicken antibodies raised against Fusarium spp. by enzyme-linked immunosorbent assay and immunoblotting

Immunoassays for the detection of three Fusarium species have been developed. Chickens were immunized with the soluble antigens from within the mycelia (mycelia-soluble antigens) and the exoantigens of Fusarium sporotrichioides, Fusarium poae and Fusarium graminearum and the antigens were characterized using enzyme-linked immunosorbent assays, immunoblotting and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The cross-reactivities of antisera with eleven species of Fusarium, eleven species of fungi from other genera and the buffer-extracts of grain were determined. Antisera to the exoantigens and mycelia-soluble antigens did not cross-react with buffer-extracts of grain. The antisera against the mycelia-soluble antigens tended to cross-react with the antigens from other genera whereas the antisera against the exoantigens were genus specific. The antiserum raised against exoantigens from F. poae was species specific. The molecular weights of the immunodominant antigens from the Fusaria were above 28 kilodaltons. Antigens from Fusaria showed specific bands in SDS-PAGE gel that can be used to produce more specific antibodies. The results suggest that exoantigen immunoassay can be developed to identify Fusarium genus, whereas mycelia-soluble antigens are not suitable for immunoidentification among genus.

Heat shock proteins and human pathogens

Recent years have seen the identification of heat shock protein 90 (HSP90) as one of sthe key immunodominant antigens in systemic fungal infection. In disseminated candidiasis, patients seroconvert when they recover from the infection. In a mouse model of infection, human, mouse, and human recombinant antibody all showed a degree of protection. HSP90 is also immunodominant in patients with an aspergilloma, allergic bronchopulmonary aspergillosis, and invasive aspergillosis who mount an antibody response. This paper argues the case for immunotherapy with antibody in treating these serious infections. Key words: heat shock protein 90, invasive candidiasis, invasive aspergillosis, immunotherapy.

Specific recognition of purified Cu,Zn superoxide dismutase from Aspergillus fumigatus by immune human sera

Sera from 22 (84.6%) of 26 patients with confirmed Aspergillus infections recognized a purified Cu,Zn superoxide dismutase from A. fumigatus on Western blots (immunoblots). Sera from 32 (71%) of 45 patients with suspected Aspergillus infections were reactive to the superoxide dismutase. Normal human sera and sera from patients with other infections were unreactive.

Monoclonal antibodies against a 97-kilodalton antigen from Aspergillus flavus

We prepared a panel of five monoclonal antibodies (MAbs) directed against Aspergillus flavus that all reacted against one 97-kDa antigen by western blot (immunoblot). Flow cytometry demonstrated that these antibodies bound (in increasing degrees) to all morphologic stages of A. flavus growth: conidia, swollen conidia, and hyphae. Cross-reactivity among species was examined by enzyme-linked immunosorbent assay of fungal culture filtrates. Four MAbs reacted with 10 of 11 A. flavus isolates, and the fifth one reacted with 9 of them. One MAb also reacted with A. fumigatus, two reacted with A. niger, A. wentii, and A. nidulans, and all five reacted with A. ochraceus. None reacted with A. terreus, A. glaucus, A. versicolor, or a Penicillium species. Each MAb bound to A. flavus hyphae in formalin-fixed paraffin sections of a muscle biopsy from a confirmed human case of invasive aspergillosis. In summary, these MAbs identified a 97-kDa antigen found on A. flavus that is both surface bound and an exoantigen. Either the same or a cross-reacting antigen is present in A. fumigatus and other Aspergillus species.

Efficacy of intravenous itraconazole against experimental pulmonary aspergillosis

The efficacy of intravenous itraconazole solubilized in hydroxypropyl-beta-cyclodextrin was assessed in a rat model of Aspergillus fumigatus pneumonia. Immunosuppressed rats were infected by intratracheal inoculation of A. fumigatus conidia. Intravenous administration of various doses of itraconazole was started immediately after infection and continued once a day for 7 days. A 10-mg dose of intravenous itraconazole per kg was as effective on survival as 1 mg of amphotericin B per kg daily (a survival rate of 100% in 28 days), while treatment with 1 mg/kg did not increase the survival rate. The 50% lethal dose of intravenous itraconazole given to immunosuppressed and uninfected rats for 7 days was 24.5 mg/kg/day. A microbiological assay to estimate accumulation in tissue after five daily intravenous administrations of itraconazole at 10 mg/kg showed that itraconazole and its active metabolites were present in the lungs for at least 6 h, reaching the MIC as previously described (B. Dupont and E. Drouchet, Rev. Infect. Dis. 9(Suppl. 1):71-76, 1987; A. Espinel-Ingroff, S. Shadomy, and R. J. Gebhart, Antimicrob. Agents Chemother. 26:5-9, 1984). Intravenous itraconazole was considered to be worth evaluating in clinical trials of aspergillosis.

An 88-kilodalton antigen secreted by Aspergillus fumigatus

An 88-kDa component secreted in vitro by Aspergillus fumigatus has been purified by sequential chromatographic procedures. The molecule is a glycoprotein with an N-linked sugar moiety composed of mannose glucose, and galactose (16:10:1). It is recognized by antibodies from patients with aspergilloma and has potential for the immunodiagnosis of aspergilloma. The antigenicity is associated with the polypeptide part of the molecule (79 kDa).

Obtenção e avaliação de antígenos de Aspergillus fumigatus

Antígenos de três amostras de A. fumigatus (354, 356, JIG) e antissoro contra a mistura destes antígenos foram produzidos e avaliados imunoquimicamente. Os antígenos de filtrado de cultura foram obtidos após concentração com acetona conforme adaptação da técnica descrita por Coleman & Kaufman. Em prova de ID obteve-se 100% de positividade com os soros de pacientes com aspergilose estudados. Com relação aos soros heterólogos encontramos reatividade com soro de um paciente com candidíase e com soro de um paciente com histoplasmose; foi encontrado padrão idêntico de resposta quando se utilizou o antígeno de referência. O antissoro foi titulado por ID, CIE e RFC MI contra o antígeno específico apresentando títulos respectivos de 1:32, 1:32 e 1:128, e utilizado para reagir contra o mesmo antígeno por IEF, demonstrando 8 linhas de precipitação, sendo 5 na região anódica e 3 na região catódica. O perfil de bandeamento do antígeno em eletroforese utilizando gel de poliacrilamida (SDS-PAGE) a 12,5% apresentou-se complexo com 26 sub-unidades protéicas, cujos pesos moleculares variaram de 18 a > 100kDa. Quando estes componentes foram eletrotransferidos e reagidos com o antissoro específico ("immunoblotting"), verificou-se imunogenicidade em todas as frações bandeadas.

Antigen detection in invasive aspergillosis

The application of a reverse passive latex agglutination test and dot-blot assay are reported in the diagnosis of 50 proven cases of invasive aspergillosis and 28 suspected cases. At a latex titre cut off of greater than or equal to 1 in 8 the test had a sensitivity of 29.4%, specificity of 96.3% and efficiency of 41.4%. This was in sera taken when the diagnosis was first suggested. The sensitivity rose to 55.1% when sera with the maximum level of antigen were examined. The dot blot was more sensitive with 33.3% of cases being positive in the initial sera. This increased to 61.5% when the serum with the maximum antigen level was taken.

Heat shock protein 88 and Aspergillus infection

Immunoblotting was used to dissect the antibody responses in the sera of 50 patients with proven invasive aspergillosis, 28 patients with suspected invasive aspergillosis, 35 patients with allergic bronchopulmonary aspergillosis, and 10 patients with an aspergilloma. This demonstrated the immunodominance of antigenic bands at 88, 84, 51, and 40 kDa. Monoclonal antibodies against the heat shock protein 90 complexes of Candida albicans and the water mold Achlya ambisexualis identified these four antigenic bands as homologous proteins. Similar antigens have been described in humans, mice, Saccharomyces cerevisiae, chickens, and Drosophila species. The antibody against A. ambisexualis has previously been shown to cross-react with antigens belonging to the human heat shock protein 90 complex. Aspergillus heat shock protein 90 was extracted from the sera of patients with invasive aspergillosis by affinity chromatography. This was done with both a rabbit hyperimmune antiserum raised against an extract of Aspergillus fumigatus NCPF 2109 and a monoclonal antibody against the heat shock protein 90 of C. albicans. In vivo expression of the antigen was demonstrated in an aspergilloma surgically removed from a patient. The role of the antigen as an allergen in allergic bronchopulmonary aspergillosis is also discussed.

Immunodiagnosis of aspergillosis

Aspergillus species are ubiquitous fungi and have been implicated as the causative agents of a variety of lung disorders in humans. These disorders include allergic, saprophytic, and systemic manifestations. The allergic disorders mainly affect atopic persons, and invasive or systemic diseases affect immunosuppressed individuals. Immunodiagnosis can help the practitioner diagnose these diseases. Demonstration of circulating antibodies is a useful criterion, but the lack of dependable and standardized antigens is a limiting factor in the diagnosis of most Aspergillus-induced diseases. Despite this limitation, however, immunodiffusion and enzyme-linked immunosorbent assays have been widely used for the detection of antibodies in the sera of patients with aspergillosis. Similarly, crude and semipurified antigens are being used to demonstrate skin hypersensitivity in patients, and several methods have been useful in the detection of antigenemia in patients with invasive aspergillosis. With a growing number of reports on the incidence of aspergillosis and an increase in the number of immunosuppressed individuals in the population, more rapid methods and more reliable reagents for immunodiagnosis are needed. With recent attempts at obtaining reliable reagents for through hybridoma technology and molecular biological techniques, substantial progress toward efficient immunodiagnosis may be achieved.

The 18-kilodalton antigen secreted by Aspergillus fumigatus

One of the major antigens secreted in vitro by Aspergillus fumigatus is an 18-kDa basic protein which has been purified by cation-exchange chromatography. It is recognized by sera from aspergilloma patients. It is also the major circulating antigen found in urine of patients with invasive aspergillosis. Our results indicated that this antigen has potential for the diagnosis of both aspergilloma and invasive aspergillosis.

Value of antigen detection in predicting invasive pulmonary aspergillosis

Two ELISAs were used to detect serum and urinary aspergillus antigen in 121 patients who were profoundly neutropenic after leukaemia therapy or bone marrow transplantation. The presence of antigen correctly predicted development of invasive pulmonary aspergillosis (IPA) in 16 patients. In 2 other cases antigen appeared after the clinical diagnosis had been made, while in only 1 case was antigen not detected. In 11 of 13 episodes of clinically suspected fungal infection antigen was detected before clinical diagnosis was made. By contrast, antigen was detected in only 1 of 90 patients who had no evidence of IPA. Both ELISAs gave positive and negative predictive values for IPA of greater than 95%, demonstrating the value of antigen detection in early diagnosis of aspergillus infection and the assay's ability to predict subsequent development of IPA. We conclude that neutropenic patients should be screened for aspergillus antigen, and propose that initial detection of fungal antigen justifies commencement of empirical antifungal therapy. Such an approach should improve the survival of patients who are at risk of developing this usually fatal infection.