Enzyme-linked immunosorbent assay and its application to the serological diagnosis of fungal infection

Identification and production of novel potential pathogen-specific biomarkers for diagnosis of histoplasmosis

IMPORTANCE

Histoplasmosis is considered one of the most important mycoses due to the increasing number of individuals susceptible to develop severe clinical forms, particularly those with HIV/AIDS or receiving immunosuppressive biological therapies, the high mortality rates reported when antifungal treatment is not initiated in a timely manner, and the limitations of conventional diagnostic methods. In this context, there is a clear need to improve the capacity of diagnostic tools to specifically detect the fungal pathogen, regardless of the patient's clinical condition or the presence of other co-infections. The proposed novel pathogen-specific biomarkers have the potential to be used in immunodiagnostic platforms and antifungal treatment monitoring in histoplasmosis. In addition, the bioinformatics strategy used in this study could be applied to identify potential diagnostic biomarkers in other models of fungal infection of public health importance.

TCF-ALP: a fluorescent probe for the selective detection of Staphylococcus bacteria and application in "smart" wound dressings

Alkaline phosphatase (ALP) is an important enzyme-based biomarker present in several bacterial species; however, it is currently undervalued as a strategy to detect pathogenic bacteria. Here, we explore our ALP-responsive colorimetric and fluorescent probe (TCF-ALP) for such applications. TCF-ALP displayed a colorimetric and fluorescence response towards Staphylococcus aureus (S. aureus), with a limit of detection of 3.7 × 106 CFU mL-1 after 24 h incubation. To our surprise, TCF-ALP proved selective towards Staphylococcus bacteria when compared with Enterococcus faecalis (E. faecalis), and Gram-negative P. aeruginosa and E. coli. Selectivity was also seen in clinically relevant S. aureus biofilms. Owing to the high prevalence and surface location of S. aureus in chronic wounds, TCF-ALP was subsequently encapsulated in polyvinyl alcohol (PVA)-based hydrogels as a proof-of-concept "smart" wound dressing. TCF-ALP hydrogels were capable of detecting S. aureus in planktonic and biofilm assays, and displayed a clear colour change from yellow to purple after 24 h incubation using ex vivo porcine skin models. Overall, TCF-ALP is a simple tool that requires no prior knowledge, training, or specialist equipment, and has the potential to overcome issues related to invasive swabbing and tissue biopsy methods. Thus, TCF-ALP could be used as a tool to monitor the early development of infection in a wound and allow for the rapid provision of appropriate treatment for Staphylococcal bacterial infections.

Comparative Study of Newer and Established Methods of Diagnosing Coccidioidal Meningitis

Meningitis is the most devastating form of coccidioidomycosis. A convenient, rapid diagnostic method could result in early treatment and avoid many meningitis complications. We studied cerebrospinal fluid (CSF) samples in patients with documented coccidioidal meningitis, and controls, with complement fixation (CF), immunodiffusion (ID) (the “classical” assays), lateral flow assays (LFA; one-strip and two-strip), and two enzyme immunoassays (EIA). The two-strip LFA and EIAs not only enabled separate testing for IgG and IgM antibodies separately, but also could aggregate results for each method. CF with ID or the aggregate use of IgG and IgM tests were considered optimal test uses. LFAs and EIAs were evaluated at 1:21 and 1:441 dilutions of specimens. All assays were compared to true patient status. With 49 patient specimens and 40 controls, this is the largest comparative study of CSF coccidioidal diagnostics. Sensitivity of these tests ranged from 71–95% and specificity 90–100%. IgM assays were less sensitive. Assays at 1:441 were similarly specific but less sensitive, suggesting that serial dilutions of samples could result in assays yielding titers. Agreement of positive results on cases was 87–100%. When kits are available, hospital laboratories in endemic areas can perform testing. LFA assays do not require a laboratory, are simple to use, and give rapid results, potentially even at the bedside.

Candidosis: diagnostic tools in the laboratory

The diagnosis of deep-seated candidosis still poses severe problems to the physician. While laboratory tests for a long time have been mainly based on the detection of antibodies to Candida and in particular Candida albicans the detection of Candida antigen in the blood gains more and more interest. When it comes to the evaluation of the various laboratory tests the correlation with autopsy data is most rewarding. The more specimens are analysed for the presence of hints at deep-seated candidosis in a given hospital setting the least frequent death due to deep-seated candidosis occurs.

DIAGNOSIS OF HISTOPLASMOSIS

Endemic mycoses can be challenging to diagnose and accurate interpretation of laboratory data is important to ensure the most appropriate treatment for the patients. Although the definitive diagnosis of histoplasmosis (HP), one of the most frequent endemic mycoses in the world, is achieved by direct diagnosis performed by micro and/or macroscopic observation of Histoplasma capsulatum (H. capsulatum), serologic evidence of this fungal infection is important since the isolation of the etiologic agents is time-consuming and insensitive. A variety of immunoassays have been used to detect specific antibodies to H. capsulatum. The most applied technique for antibody detection is immunodiffusion with sensitivity between 70 to 100 % and specificity of 100%, depending on the clinical form. The complement fixation (CF) test, a methodology extensively used on the past, is less specific (60 to 90%). Detecting fungal antigens by immunoassays is valuable in immunocompromised individuals where such assays achieve positive predictive values of 96-98%. Most current tests in diagnostic laboratories still utilize unpurified antigenic complexes from either whole fungal cells or their culture filtrates. Emphasis has shifted, however, to clinical immunoassays using highly purified and well-characterized antigens including recombinant antigens. In this paper, we review the current conventional diagnostic tools, such as complement fixation and immunodiffusion, outline the development of novel diagnostic reagents and methods, and discuss their relative merits and disadvantages to the immunodiagnostic of this mycosis.

Specific antibody detection in human aspergillosis: a GEMO* multicentre evaluation of a rapid immunoelectrophoresis method (Paragon). Group d'Etude des Mycoses Opportunistes

A new immunoelectrophoresis system, the Paragon system, was evaluated in three different hospital centres with the aim of improving standardization of the serodiagnosis of human aspergillosis. To select the most efficient antigen, various commercial and home-made antigens were first tested on 19 sera from 19 patients with highly probable aspergillosis. The value measured using the Paragon anti-Aspergillus antibody detection system was then compared with the results obtained by conventional serological diagnostic methods (conventional immunoelectrophoresis, enzyme linked-immunosorbent assay, indirect immunofluorescence): this step was performed using the first 19 sera as well as 16 other sera from 13 patients with suspected aspergillosis. Concordant results were obtained in 28 cases. The discrepancies observed with seven sera were probably related to differences in the nature of the antigens. Paragon immunoelectrophoresis proved to be a practicable technique requiring only a small amount of serum and giving results within a shorter time than competitive methods (24-48 h). Its major drawbacks compared with conventional immunoelectrophoresis are some difficulties in reading, fewer precipitin lines and the relatively high cost of routine analysis.

Clinical laboratory applications of monoclonal antibodies

Monoclonal antibody (MAb) technology is well recognized as a significant development for producing specific serologic reagents to a wide variety of antigens in unlimited amounts. These reagents have provided the means for developing a number of highly specific and reproducible immunological assays for rapid and accurate diagnosis of an extensive list of diseases, including infectious diseases. The impact that MAbs have had in characterizing infectious disease pathogens, as well as their current and future applications for use in clinical microbiology laboratories, is reviewed. In addition, the advantages (and disadvantages) of the use of MAbs in a number of immunoassays, such as particle agglutination, radioimmunoassays, enzyme-linked immunosorbent assays, immunofluorescent-antibody assays, and immunohistology, are explored, including the use of these reagents in novel test system assays. Also, nucleic acid probe technology is compared with the use of MAbs from the perspective of their respective applications in the diagnosis of infectious disease agents. There is no question that hybridoma technology has the potential to alter significantly the methods currently used in most clinical microbiology laboratories.

Use of a urease-antibody conjugate in an enzyme immunoassay for the detection of blastomycosis

A urease-antibody conjugate was used in an enzyme-linked immunoassay (ELISA) for the detection of antibodies in blastomycosis. A Blastomyces dermatitidis immunodiffusion antigen was used as the reference antigen in a solid phase indirect ELISA procedure and the endpoints were determined visually. Urease ELISA results on serum specimens from patients with blastomycosis compared favorably (90%) with results obtained spectrophotometrically by the alkaline phosphatase enzyme system. Specificity was evaluated with assays on sera from patients with histoplasmosis (20% cross reactivity), coccidioidomycosis (0% cross reactivity) and on Histoplasma capsulatum skin-test positive individuals (0% cross reactivity). The ease of performance of the urease ELISA combined with no requirements for specialized spectrophometric equipment are factors that favor the continued development of the test as an alternative serodiagnostic method. The assay may prove to be useful and a valuable adjunct to fungal antibody screening procedures.

Pathogenetic and serological aspects of pulmonary aspergillosis

Af is an important pathogen of the bronchopulmonary system, and the clinical spectrum encompasses aspergilloma, CNPA, IPA, ABPA, bronchial asthma, and allergic alveolitis. Bronchial carriage may, however, not always be associated with pathological effects. The polymorphism of the aspergillus-related disorders seems mostly to depend upon the different responses of the hosts. This review considers the antigenic composition of Af and specific antibody responses in man in relation to the pathogenesis and diagnosis of the various forms of pulmonary aspergillosis. More than 200 macromolecular components have been listed for Af and more than 30 antigens found to react with human sera. Serum antibodies to Af are common in healthy subjects. Schønheyder and his associates (A-L) have shown that IgG, IgA and IgM antibodies in healthy subjects are directed towards antigens to which also patients with aspergillosis strongly react. With immunofluorescent staining these antigens were found to be associated with hyphal walls, and a MW 470,000 fraction from ruptured mycelium was most reactive in ELISA. The respiratory tract appears to be the major route for exposure since the humoral responses include IgA class antibodies, and sIgA antibodies are found in bronchial secretions. Moreover, IgG antibody levels to the MW 470,000 fraction correlate with occupational exposure and smoking habits. In patients with cystic fibrosis high IgG antibody levels to MW 470,000 and MW 25,000-50,000 antigen fractions were associated with the carriage of Af in the sputum. An individual patient's level of IgA antibodies to the MW 470,000 fraction was inversely related to the Af carrier rate, and this was also true for IgE dependent reactivity to Af antigens. These observations indicate that IgG antibodies to some antigens mirror the extent of antigenic exposure, whereas some IgA and IgE antibodies may play a protective role against bronchial colonization with Af. IgG antibody determinations by ELISA were found to provide a higher diagnostic efficacy in pulmonary aspergillosis than IgA antibody assays. With IgG antibodies there were statistically significant differences between patients and the controls and there was little overlap of ELISA values between the groups. The fractions of MW 250,000 with catalase activity and MW 25,000-50,000 with protease activity, were most suitable for serological diagnosis. A gel immunoelectrophoretic assay proved Af catalase to be a major diagnostic antigen in patients with aspergilloma or with an apical aspergillus lung infiltrate.(ABSTRACT TRUNCATED AT 400 WORDS)

Production and partial characterization of anti-Candida monoclonal antibodies

Spleen cells of Biozzi HR mice immunized with formolized, lyophilized Candida albicans serotype A cells were fused with P3-X63-Ag8.653 mouse myeloma cells. Twenty-one monoclonal antibodies (mAb) selected by an indirect ELISA technique were produced and partially characterized. All mAb reacted with a C. albicans cell wall extract. Five of the mAb were directed against C. albicans serotype A, but not against serotype B. These mAb also recognized C. tropicalis. The 16 other mAb cross-reacted with several yeast species. The immunoreactivity profiles of 5 representative anti-Candida mAb were confirmed in most cases by inhibition studies.

Antibody to Aspergillus fumigatus antigens in normal sera: influence on positive-negative discrimination in ELISA

The response of precipitin-negative sera from non-selected asthmatic patients against a range of somatic and culture filtrate antigens of Aspergillus fumigatus in ELISA for anti-A. fumigatus IgG is described. Antibody to the various antigens was widely distributed but the precise distribution was dependent upon antigen type. To determine how the selection of negative reference sera from precipitin-negative sera can influence the discrimination between precipitin-positive and -negative sera in ELISA, panels of 10 sera were chosen from the extremes of the frequency distribution and by random selection. The closest agreement between precipitin testing and ELISA was seen when randomly-selected negative reference sera were incorporated in the assay, although the degree of correlation was dependent upon the detector antigen. These findings demonstrate the requirement for careful selection of sera included as negative reference sera in ELISA for anti-A. fumigatus IgG.

Serological tests in the diagnosis of pulmonary aspergillosis

Sera from 44 patients with clinically suspected pulmonary aspergillosis (mainly of an allergic type) were examined for antibodies to Aspergillus fumigatus using an enzyme-linked immunosorbent assay (ELISA) and counter-immunoelectrophoresis (CIE). Of the sera, 15 were considered to contain Aspergillus antibodies using ELISA; 11 of these also contained precipitins by CIE. In no instance was a CIE-positive serum negative by ELISA. The serum of 1 patient with autopsy-verified invasive pulmonary aspergillosis was negative in both tests. Protein-enriched antigens derived by ammonium sulphate precipitation of crude hyphal homogenates seemed of most use in ELISAs. In addition, 4 of 8 sera obtained from patients with possibly invasive candidosis also revealed significant levels of Aspergillus antibody by ELISA (but not CIE). All of the 8 sera contained readily detectable Candida precipitins by CIE. Problems of potential cross-reactivity obviously need careful consideration with ELISAs. Our results suggest that ELISA procedures under appropriately controlled conditions are more sensitive than CIE for detecting Aspergillus antibodies. However it seems that some patients with invasive aspergillosis will be antibody-negative even with sensitive tests such as ELISA.

Antigen and antibody attachment in ELISA for Aspergillus fumigatus IgG antibodies

Four commercial antigen extracts of Aspergillus fumigatus were evaluated for use in a rapid enzyme-linked immunosorbent assay (ELISA) for anti-A. fumigatus IgG. Initial binding of both somatic and culture filtrate preparations to a polyvinyl chloride solid phase was concentration dependent and increased with incubation time. Antigen binding to the solid phase was reproducible. Binding of A. fumigatus precipitin-positive serum to bound antigen was rapid. All four A. fumigatus antigens demonstrated similar dose-response curves when tested against pooled sera containing a high titre of A. fumigatus antibodies. Detectable activity in precipitin test-negative sera decreased rapidly with dilution. All the antigen preparations were found to be suitable for ELISA procedures and permit the rapid determination of IgG antibodies to A. fumigatus.

Magnetic enzyme-linked immunosorbent assay (MELISA) for determination of specific IgG in paracoccidioidomycosis

A magnetic solid phase enzyme-linked immunosorbent assay (MELISA) for quantification of IgG antibodies to somatic and metabolic antigens of Paracoccidioides brasiliensis was developed. Activation of magnetic polyacrylamide agarose beads with concanavalin A was superior to glutaraldehyde activation, and test sensitivity was higher for somatic than for metabolic antigens. Comparative MELISA, counterimmunoelectrophoresis and erythroimmunoassay tests with sera from 33 proven cases of paracoccidioidomycosis, 14 cases of histoplasmosis and 20 normal human sera showed the MELISA could distinguish antibody levels in paracoccidioidomycosis from those in normal sera; however two sera from histoplasmosis cases cross-reacted in the MELISA. MELISA is a rapid test (5-6 h) and the results suggest it has considerable potential value for assay of anti-P. brasiliensis antibodies.

Diagnostic significance of the human antibody response to a major cytoplasmic antigen of C. albicans

In contrast to the ubiquitous presence of IgG antibodies to mannan or to crude antigen preparations of C. albicans (CA), antibodies to a purified cytoplasmic antigen (SSF) of CA were detected by ELISA only in patients with candidiasis. The differences of mean absorbancy values found in different groups of sera can allow the distinction of normal sensitized controls from patients with candidiasis and can also distinguish between patients with different degrees of C. albicans invasion.