Evaluation of various plastic microtiter plates with measles, toxoplasma, and gamma globulin antigens in enzyme-linked immunosorbent assays

Consequences of the Edge Effect in a Commercial Enzyme-Linked Immunosorbent Assay for the Diagnosis of Lyme Neuroborreliosis

The diagnosis of Lyme neuroborreliosis (LNB) is based on neurological symptoms, cerebrospinal fluid (CSF) pleocytosis, and intrathecally produced Borrelia-specific antibodies. In most cases, the presence of intrathecally produced Borrelia-specific antibodies is determined by using an enzyme-linked immunosorbent assay (ELISA). The edge effect is a known phenomenon in ELISAs and can negatively influence the assay reproducibility and repeatability, as well as index calculations of sample pairs which are tested in the same run. For LNB diagnostics, an index calculation is used for which the relative amounts of Borrelia-specific antibodies in CSF and serum are measured to calculate a CSF/serum quotient, which is needed to calculate the Borrelia-specific antibody index (AI). The presence of an edge effect in an ELISA used for LNB diagnostics may thus have implications. In this study, we investigated the intra-assay variation of the commercial Enzygnost Lyme link VlsE/IgG ELISA used for LNB diagnostics and showed the presence of an edge effect. Minor adaptations in the ELISA protocol decreased this effect. The adapted protocol was subsequently used to test 149 CSF-serum pairs of consecutive patients received in a routine diagnostic laboratory. By simulation, we showed that, if the standard protocol would have been used, then the edge effect for this study population could have resulted in 15 (10.1%) false-pathological and two (1.3%) false-normal Borrelia-specific IgG AIs. Thus, the observed edge effect can lead to inaccurate LNB diagnoses. Our study underlines that the edge effect should be investigated when ELISAs are implemented in routine diagnostics, as this phenomenon can occur in any ELISA.

Microwell Plate-Based Dynamic Light Scattering as a High-Throughput Characterization Tool in Biopharmaceutical Development

High-throughput light scattering instruments are widely used in screening of biopharmaceutical formulations and can be easily incorporated into processes by utilizing multi-well plate formats. High-throughput plate readers are helpful tools to assess the aggregation tendency and colloidal stability of biological drug candidates based on the diffusion self-interaction parameter (k_D). However, plate readers evoke issues about the precision and variability of determined data. In this article, we report about the statistical evaluation of intra- and inter-plate variability (384-well plates) for the k_D analysis of protein and peptide solutions. ANOVA revealed no significant differences between the runs. In conclusion, the reliability and precision of k_D was dependent on the plate position of the sample replicates and k_D value. Positive k_D values (57.0 mL/g, coefficients of variation (CV) 8.9%) showed a lower variability compared to negative k_D values (−14.8 mL/g, CV 13.4%). The variability of k_D was not reduced using more data points (120 vs. 30). A k_D analysis exclusively based on center wells showed a lower CV (<2%) compared to edge wells (5–12%) or a combination of edge and center wells (2–5%). We present plate designs for k_D analysis within the early formulation development, screening up to 20 formulations consuming less than 50 mg of active pharmaceutical ingredient (API).

Abrasive treatment of microtiter plates improves the reproducibility of bacterial biofilm assays

Microtiter plate-based bacterial biofilm assay is frequently used to study bacterial biofilm development and growth. While this assay is simple and relatively high-throughput, it frequently shows difficulty in establishing robust biofilm attachment in the wells. We report that the consistency of bacterial biofilm assays carried out in microtiter plates subjected to abrasive treatment, by sandblasting or drill press grinding, is significantly improved in a Pseudomonas fluorescens Pf0-1 model. Scanning electron microscopy imaging suggests that the treated surfaces could provide points of attachment to facilitate the recruitment of bacteria in the initial phase of biofilm colony establishment. The sandblast treated polypropylene, but not polystyrene, plates were found suitable in studying the impact of flavonoid quercetin on the biofilm formation in Bacillus subtilis FB17. Further investigation revealed that due to the hydrophobicity of the polystyrene surfaces, a greater amount of quercetin was adsorbed on the plate surface, effectively lowering the concentration of the flavonoid in solution.

The reproducibility of bacterial biofilm assays is improved using abrasively-treated microtiter plates.

Variability in Microplate Surface Properties and Its Impact on ELISA

BACKGROUND

Microplate-based immunoassays are widely used in clinical and research settings to measure a broad range of biomarkers present in complex matrices. Assay variability within and between microplates can give rise to false-negative and false-positive results leading to incorrect conclusions. To date, the contribution of microplates to this variability remains poorly characterized and described. This study provides new insights into variability in immunoassays attributable to surface characteristics of commercial microplates.

METHODS

Well-to-well assay variation in γ-treated and nontreated 96-well opaque microplates suitable for chemiluminescence assays was determined by use of a validated sandwich ELISA. Microplate surface characteristics were assessed by sessile drop contact angle measurements, scanning electron microscopy, energy dispersive x-ray spectroscopy, and atomic force microscopy.

RESULTS

All microplate types tested exhibited vendor-specific assay response profiles; and "rogue" plates with very high intraassay variation and deviant mean assay responses were found. Within-plate, location-dependent bias in assay responses and variability in well contact angle were also observed. We demonstrate substantial differences in well-surface properties with putative effects on protein-coating reproducibility and hence consistency in immunoassay responses. A surface "cleaning" effect on manufacturing residues was attributed to γ-irradiation, and treated microplates manifest increased polar functionalities, surface roughness, and assay responses.

CONCLUSIONS

Our data suggest that tighter control of variability in surface roughness, wettability, chemistry, and level of residual contaminants during microplate preparation is warranted to improve consistency of ELISA assay read out.

A Simple Technique for Reducing Edge Effect in Cell-Based Assays

Several factors are known to increase the noise and variability of cell-based assays used for high-throughput screening. In particular, edge effects can result in an unacceptably high plate rejection rate in screening runs. In an effort to minimize these variations, the authors analyzed a number of factors that could contribute to edge effects in cell-based assays. They found that pre-incubation of newly seeded plates in ambient conditions (air at room temperature) resulted in even distribution of the cells in each well. In contrast, when newly seeded plates were placed directly in the CO2 incubator, an uneven distribution of cells occurred in wells around the plate periphery, resulting in increased edge effect. Here, the authors show that the simple, inexpensive approach of incubating newly seeded plates at room temperature before placing them in a 37° C CO2 incubator yields a significant reduction in edge effect. ( Journal of Biomolecular Screening 2003:566-570)

Insulin-like growth factor I in cats: validation of an enzyme-linked immunosorbent assay and determination of biologic variation

BACKGROUND

Insulin-like growth factor I (IGF-I) measurements are used in veterinary medicine for diagnosing growth hormone disorders. IGF-I assays are subject to interference by IGF-binding proteins (IGFBP) which may not be efficiently removed by standard extraction methods. Adding excess IGF-II during analysis may improve accuracy.

OBJECTIVES

The purpose of the study was to validate a commercial human IGF-I ELISA which uses excess IGF-II for feline samples and to evaluate biologic variation.

METHODS

Precision was determined by calculating the coefficient of variation (CV). Accuracy was determined by recovery after removal of IGFBP, addition of IGF-I, and linear dilution after the addition of IGFBP. Biologic variation was determined by repeated sampling in 7 cats.

RESULTS

There was interference by IGFBP in the high measuring range, resulting in falsely low IGF-I concentrations. This was overcome by the addition of high concentrations of IGF-II. Untreated serum had a measured/expected ratio of 98-115% compared to serum where IGFBP had been removed. Recovery after the addition of IGF-I was 83-112%. Inter- and intra-assay CVs ranged from 2.4% to 5.0% which is within the minimum acceptance criteria based on biologic variation. The reference interval of IGF-I was wide (90-1207 ng/mL) and there was a significant association between body weight and ln IGF-I (P < .000001).

CONCLUSIONS

This human ELISA is suitable for feline samples, but interfering IGFBP can cause falsely low concentrations. It is recommended to dilute samples such that IGF-I is < 28 ng/mL on the standard curve to grant for sufficient IGF-II for binding of interferent IGFBP.

Development of a versatile enzyme immunoassay for non-invasive assessment of glucocorticoid metabolites in a diversity of taxonomic species

Endocrinology is a useful tool for conservation biologists and animal managers, and measuring glucocorticoids can help understand biological mechanisms associated with species decline and animal welfare. The current study describes the development and optimization of a glucocorticoid enzyme immunoassay (EIA) to non-invasively assess adrenal activity in a variety of taxa. The antiserum (CJM006) was raised in rabbits to a corticosterone-3-CMO-BSA immunogen and used in a standard competitive EIA system. However, the EIA initially produced results with unacceptably high inter-assay variation, attributed to consistent patterns observed within the optical density of developing plates. To determine the cause of this variability, a number of factors were examined using synthetic corticosterone standard and endogenous faecal extract, including: plate type (Nunc MaxiSorp® II versus Immulon IB plates); the use of non-specific secondary antibody; type (artificial versus natural) and presence (light versus dark) of light during incubation; plate loading temperature (4°C versus room temperature); and substrate reagent temperature (4°C versus room temperature). Results indicated that variability was associated with plate location effects, which were not initially detected because control samples were always run in the same positions across plates. Light and temperature were the two major factors that affected EIA reliability. For this assay, the standard protocol required slight modification, with the optimal protocol using Nunc MaxiSorp® plates, room temperature substrate reagents and dark incubation conditions. Following optimization, this EIA was then validated biochemically for 38 species, through parallel displacement curves and interference assessment tests of faecal and urine samples. Additionally, biological validation was performed opportunistically in a subset of species, with use of this EIA demonstrating significant elevations in faecal glucocorticoid metabolites following potentially challenging events. In summary, this glucocorticoid EIA cross-reacts with excreted glucocorticoid metabolites across a wide range of taxa, including ungulates, primates, felids, birds, rodents and amphibians. We conclude that when used with optimal reagent and incubation conditions, this EIA will be useful for non-invasive monitoring of adrenal activity in a wide range of wildlife species.

Inhibition of basophil activation by histamine: a sensitive and reproducible model for the study of the biological activity of high dilutions

BACKGROUND

At the beginning of this series of experiments we were looking for a model based on the use of purified commercially available compounds based on a fully described and accepted pharmacological model to study of the biological effect of high dilutions. Negative feedback induced by histamine, a major pro-inflammatory mediator, on basophils and mast cells activation via an H2 receptor me these criteria. The simplest way of measuring basophil activation in the early 1980's was the human basophil activation test (HBDT).

OBJECTIVES

Our major goal was first to study the biological effect of centesimal histamine dilutions beyond the Avogadro limit, on the staining properties of human basophils activated by an allergen extract initially house dust mite, then an anti-IgE and N-formyl-Met-Leu-Phe (fMLP). Technical development over the 25 years of our work led us to replace the manual basophil counting by flow cytometry. The main advantages were automation and observer independence. Using this latter protocol our aim was to confirm the existence of this phenomenon and to check its specificity by testing, under the same conditions, inactive analogues of histamine and histamine antagonists. More recently, we developed an animal model (mouse basophils) to study the effect of histamine on histamine release.

METHODS AND RESULTS

For the HBDT model basophils were obtained by sedimentation of human blood taken on EDTA and stained with Alcian blue. Results were expressed in percentage activation. Histamine dilutions tested were freshly prepared in the lab by successive centesimal dilutions and vortexing. Water controls were prepared in the same way. For the flow cytometric protocol basophils were first labeled by an anti-IgE FITC (basophil marker) and an anti-CD63 (basophil activation marker). Results were expressed in percentage of CD63 positive basophils. Another flow cytometric protocol has been developed more recently, based on basophil labeling by anti-IgE FITC (fluorescein isothiocyanate) and anti-CD203 PE (another human basophil activation marker). Results were expressed in mean fluorescence intensity of the CD203c positive population (MFI-CD203c) and an activation index calculated by an algorithm. For the mouse basophil model, histamine was measured spectrofluorimetrically. The main results obtained over 28 years of work was the demonstration of a reproducible inhibition of human basophil activation by high dilutions of histamine, the effect peaks in the range of 15-17CH. The effect was not significant when histamine was replaced by histidine (a histamine precursor) or cimetidine (histamine H2 receptor antagonist) was added to the incubation medium. These results were confirmed by flow cytometry. Using the latter technique, we also showed that 4-Methyl histamine (H2 agonist) induced a similar effect, in contrast to 1-Methyl histamine, an inactive histamine metabolite. Using the mouse model, we showed that histamine high dilutions, in the same range of dilutions, inhibited histamine release.

CONCLUSIONS

Successively, using different models to study of human and murine basophil activation, we demonstrated that high dilutions of histamine, in the range of 15-17CH induce a reproducible biological effect. This phenomenon has been confirmed by a multi-center study using the HBDT model and by at least three independent laboratories by flow cytometry. The specificity of the observed effect was confirmed, versus the water controls at the same dilution level by the absence of biological activity of inactive compounds such as histidine and 1-Methyl histamine and by the reversibility of this effect in the presence of a histamine receptor H2 antagonist.

Competitive electrochemiluminescence wash and no-wash immunoassays for detection of serum antibodies to smooth Brucella strains

Brucellosis is a bacterial zoonotic disease of major global importance. Natural hosts for Brucella species include animals of economic significance, such as cattle and small ruminants. Controlling brucellosis in natural hosts by high-throughput serological testing followed by the slaughter of seropositive animals helps to prevent disease transmission. This study aimed to convert an existing competitive enzyme-linked immunosorbent assay (cELISA), used for the serodiagnosis of brucellosis in ruminants, to two electrochemiluminescence (ECL) immunoassays on the Meso Scale Discovery (MSD) platform. The first assay employed a conventional plate washing step as part of the protocol. The second was a no-wash assay, made possible by the proximity-based nature of ECL signal generation by the MSD platform. Both ECL wash and no-wash assays closely matched the parent cELISA for diagnostic sensitivity and specificity. The results also demonstrated that both ECL assays met World Organization for Animal Health (OIE) standards, as defined by results for the OIE standard serum (OIEELISA(SP)SS). This report is the first to describe an ECL assay incorporating lipopolysaccharide, an ECL assay for serodiagnosis of a bacterial infectious disease, a separation-free (no-wash) ECL assay for the detection of serum antibodies, and the use of the MSD platform for serodiagnosis. The simple conversion of the cELISA to the MSD platform suggests that many other serodiagnostic tests could readily be converted. Furthermore, the alignment of these results with the multiplex capability of the MSD platform offers the potential of no-wash multiplex assays to screen for several diseases.

Improvement of viral recombinant protein-based immunoassays using nanostructured hybrids as solid support

Protein adsorption onto solid surfaces is a complex process playing an important role in biological systems, being crucial to maintain the three-dimensional conformation during molecules interaction. Polymers hybrid network could be used to perform immunoassays with the required high level specificity. We have developed a novel route for incorporating recombinant protein from Bovine Herpesvirus into a network using as template Poly(vinyl alcohol) chemically tailored with five organosilanes followed by FTIR spectroscopy characterization. Protein expressed in E. coli was incorporated into hybrid network; all the PVA-hybrids interacted with this biomolecule and FTIR vibrational bands have endorsed the results. PVA hybrids modified with 3-(triethoxysilyl) propylisocyanate-TESPI presented the best result in the immunoassay, enhancing the sera specificity in comparison with the commercial microplate. We have successfully developed organic-inorganic hybrid based on PVA-silane to be used in serological tests with recombinant protein as a promising tool for the development and production new diagnostic assays.

Development of fluorescence-linked immunosorbent assay for high throughput screening of interferon-gamma

BACKGROUND

Human interferon-gamma (hIFN-gamma) is produced by lymphocytes and has a variety of biological properties. Measurement of hIFN-gamma is widely used for various immunological responses for allergic or autoimmune diseases. Enzyme-linked immunosorbent assay (ELISA) is an established immunoassay used to quantify cellular metabolites or cytokines. ELISA requires many incubation and wash steps and is not practically suitable for screening large numbers of samples.

METHODS

We have developed a fluorescence-linked immunosorbent assay (FLISA) method for the detection of hIFN-gamma. We measured the 50% inhibitory concentration (IC50) value of the hIFN-gamma production by interleukin (IL)-18 binding protein and anti-IL-18 monoclonal antibody. The IC50 described by FLISA was compared with that by ELISA.

RESULTS

We developed a new system for measuring hIFN-gamma using Allophycocyanine (APC) fluorescent protein and compared it with the previous method using Cy5.5. The proposed FLISA had a smaller coefficient of variation than ELISA, and the means of coefficient of variation using the same samples measured by ELISA and FLISA were, respectively, 11.1% and 3.8%, suggesting that the edge effect often giving non-specific results may be smaller in FLISA than in ELISA.

CONCLUSIONS

The improved FLISA system proposed is ideally suited for efficient measurements of hIFN-gamma. This homogeneous and multiplex method will be a powerful tool for high throughput screening for drug discovery research.

Comparative evaluation of a field-based dot-ELISA kit with three other serological tests for the detection of Brucella antibodies in goats

A dot-ELISA (d-ELISA) test was evaluated and compared with the serum agglutination test (SAT), micro-complement fixation test (CFT) and a plate-ELISA (p-ELISA) for field use in screening herds of goats against brucellosis. During the standardization of the dot-ELISA kit on 1732 caprine serum samples, 1571 samples out of 1666 were found to be negative in d-ELISA, SAT and micro-CFT, while 59 were positive in different combinations. Of a further 66 serum samples, 34 were negative and 31 were positive in different combinations in d-ELISA, SAT, micro-CFT and p-ELISA. A total of 1584 goats belonging to different herds were then screened for brucellosis. Of the 694 serum samples screened in the first batch using d-ELISA, a positive reaction was observed in 26 cases. Further screening of these cases revealed 13 and 21 goats as positive reactors in SAT and CFT, respectively. In a second batch of 890 goats there were 109 positive reactors in d-ELISA. Among these 109 goats, 34, 40 and 80 goats were positive reactors in SAT, CFT and p-ELISA, respectively. The results of d-ELISA correlated well with those of p-ELISA. Dot-ELISA was found to be a more suitable and rapid test for screening large numbers of goats in the field.

Application of the bootstrap to calibration experiments

In calibration experiments, a number of samples of known concentration are used to establish the relationship between a measured response and sample concentration; this relationship is then used to estimate the unknown concentration of further samples from their measured responses. In addition to the estimates themselves, it is useful to have available some measure of their precision, usually given in the form of confidence limits. The standard method of inverting prediction limits is found to work well in simple situations, but in nonlinear multivariate calibration it becomes intractable. The bootstrap offers an alternative methodology, but in the calibration framework its application is not obvious. We describe some considerations in bootstrapping calibration data and compare our methods with a previous attempt and with the standard method in linear, nonlinear, and multivariate situations. The bootstrap is found to be a useful tool in those situations where the standard method is difficult to implement.

A sensitive enzyme immunoassay for angiotensin II in serum

A sensitive and specific enzyme immunoassay for measuring angiotensin II (AII) has been developed as a convenient alternative to a radioimmunoassay. An antiserum to AII was prepared using AII conjugated by carbodi-imide to rabbit serum albumin, and coated on to microwell plates. The labelled antigen was prepared from AII and horseradish peroxidase using the periodate method. This enzyme immunoassay was a simple two-step procedure: 0.1 ml of AII-extracted plasma was incubated for 1 h at 37 degrees C; and 1 ml of labeled AII was incubated for 1 h at 37 degrees C. Bound horseradish peroxidase activity was then determined using o-phenylenediamine as chromogen by measuring the absorbance at 492 nm. The lower detection limit of the assay was 3.5 pmol l-1. Between- and within-assay RSD values were 8.8-18.3% and 6.9-17%, respectively, for concentrations of 10-40 pmol l-1. The accuracy of the assay, determined by recovery and linearity experiments, was 89-106% for recovery and 91-126% for parallelism. The results obtained by the present ELISA method were well correlated with those obtained by an established radioimmunoassay (n = 10, r = 0.96, intercept = 0.9 and slope = 1.02). This assay is easy to perform, rapid and does not require radioisotopes; thus it could be widely applied in clinical laboratories.

Covalent coupling of a steroid to microwell plates for use in a competitive enzyme-linked immunosorbent assay

The covalent coupling of a model steroid, 17 alpha-hydroxypregnenolone, to the wells of the microtiter plate, CovaLink NH, for use in a competitive enzyme-linked immunosorbent assay is described. This plate has secondary amino groups bound to its surface. A carboxylated derivative of the steroid was coupled to the amino group to form an amide bond in a single step using a water-soluble carbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (10 mM) as coupling reagent in the presence of N-hydroxysuccinimide (1 mM). After carrying out a competitive immune reaction, antibodies bound to immobilized steroids were estimated by means of a second antibody-enzyme conjugate. The non-specific background was reduced with blocking agents which did not interfere with the immune reaction between antibodies and the steroids coupled to the plastic surface. The following two procedures were effective for this purpose: pretreatment of wells with 0.01% Tween 20 solution followed by 0.5% bovine serum albumin in phosphate buffered saline, and addition of 0.01% Tween 20 to the assay buffer. With this method, the preparation of steroid-enzyme conjugates is unnecessary and optimization of conditions for ELISA procedures can be achieved in a simple manner.

Immunoenzymatic techniques applied to the specific detection of nucleic acids. A review

Numerous enzymatic and chemical methods are now available for the preparation of non-radioactive nucleic acid probes. Labels, such as enzymes, fluorophores, lumiphores can be attached to the nucleic acid probe either by covalent bonds (direct labelling) or by biospecific recognition after hybridization (indirect labelling). The principle of the latter method is based on the use of a hapten-labelled nucleic acid probe which is generally detected by an immunoenzymatic assay. Indirect labelling has several advantages: this procedure uses multienzyme complexes to increase the number of enzyme molecules associated with hybridization and hence provides an increase in detectability; moreover, haptens (biotin, dinitrophenol, acetylaminofluorene analogues, digoxigenin, brominated or sulphonylated pyrimidines) used to label nucleic acid probes are not sensitive to elevated temperatures (42-80 degrees C), extended incubation times (several hours), detergents and organic solvents currently required in hybridization techniques. The application of the immunoenzymatic and related techniques to nucleic acid probing is reviewed, focussing on the strategies of non-radioactive hybridization, hapten-labelling of nucleic acids and methods for the immunodetection of the hybrids.

Detection of point mutation in bla T genes of Enterobacteriaceae by biotinylated oligonucleotide probes using microwell hybridization and enzymofluorometric method

Point mutation in the nucleotide sequence of the structural genes for the TEM-type penicillinases can broaden their substrate spectrum towards all beta-lactams except cephamicins and imipenem. We describe here hybridization techniques for the detection of point mutations by non-radioactive oligonucleotide probes with plasmid DNA carrying bla T genes immobilized in polystyrene microwells. After hybridization in discriminating conditions with corresponding biotinylated oligonucleotide probes, the hybrids were detected by using a streptavidin-alkaline phosphatase conjugate and a fluorogenic substrate, 4-methylumbelliferyl-phosphate. The adsorption of DNA to microwells used in the present work was found to be independent of Mg2+ and Na+ concentrations. By this method, less than 3 fmols of target DNA were sufficient for the detection of point mutation.

A dot-immunobinding assay for the laboratory diagnosis of tuberculous meningitis and its comparison with enzyme-linked immunosorbent assay

In an attempt to establish an alternative to standard bacteriological methods in the laboratory diagnosis of tuberculous meningitis (TBM), a simple dot-immunobinding assay (Dot-Iba) was standardized to detect Mycobacterium tuberculosis antigen 5 and antimycobacterial antibody in cerebrospinal fluid (CSF) specimens of patients with TBM. Sensitivity and specificity of Dot-Iba was compared with conventional enzyme-linked immunosorbent assay (ELISA) and standard bacteriological techniques. The Dot-Iba showed excellent correlation with indirect ELISA for the detection of antimycobacterial antibody in CSF and showed 60% sensitivity and 100% specificity in culture-negative patients with TBM. However Dot-Iba was less sensitive for the detection of antigen 5 in CSFs and showed false negative results (60%) in culture-positive patients with TBM.

Rapid diagnosis of tuberculous meningitis with a dot enzyme immunoassay to detect antibody in cerebrospinal fluid

A simple dot enzyme immunoassay (Dot-EIA) was carried out to detect antibody to Mycobacterium tuberculosis antigen 5 in cerebrospinal fluid (CSF) specimens from 40 patients with a clinical diagnosis of tuberculous meningitis (TBM). The assay gave a positive reaction in all ten patients with culture proven TBM. In 30 culture negative patients with TBM, the assay was positive at a titre of 1:16 in 18 patients. In 40 patients with non-tuberculous neurological diseases (control group) the assay was negative at a titre of 1:16. The Dot-EIA had an overall sensitivity of 70% and a specificity of 100% in the diagnosis of TBM. This assay could be used as a rapid screening test to establish the diagnosis of TBM, particularly in patients in whom bacteriological investigations for Mycobacterium tuberculosis in CSF specimens are negative.

Comparison of an enzyme-linked immunosorbent assay to an indirect immunofluorescence assay for the detection of antibodies to Borrelia burgdorferi in the dog

An enzyme-linked immunosorbent assay (ELISA) was compared to an indirect immunofluorescence assay (IFA) for detection of IgG antibodies to Borrelia burgdorferi in dog sera. The concordance of the two tests was 93.5% for sera from dogs from Maryland (n = 93), 98.0% for sera from dogs from North Carolina (n = 446), and 97.2% for the combined sample groups (n = 539). Twenty-five of the 27 samples with discordant or low positive results were tested, and showed immunoblot reactions to 1 to 10 different bands. Reaction patterns and intensity of the bands were quite variable, and did not explain a reason for the discordance.

Interlaboratory comparison of titers of antibody to Borrelia burgdorferi and evaluation of a commercial assay using canine sera

Sixty canine serum samples were sent to 10 different diagnostic laboratories for anti-Borrelia burgdorferi antibody analysis. All laboratories knew of the study prior to receiving the samples. Agreement among all laboratories for all interpretations was 91% (546 of 600 samples). There was complete agreement among all the laboratories for only 32 (53%) of the samples. Most of the disagreements were due to differences reported by either one (15 samples) or two (7 samples) laboratories per sample. When discrepancies in interpretations existed, the interpretation reported by the majority of the laboratories was considered the standard for comparison. One laboratory had no discrepant interpretations from this standard, while the laboratory with the most discrepancies had 16. The median number of discrepancies per laboratory was five. By using pairwise comparisons between each laboratory and the majority standard, eight of the laboratories showed strong agreement and the remaining two showed fair to good agreement. The type of test used (enzyme-linked immunosorbent assay versus indirect immunofluorescence assay) did not appear to influence the number of discrepant interpretations reported. Sera considered to be positive by the majority of the laboratories usually reacted to more than five antigens in immunoblots, with at least three or more of those being intense reactions. For positive samples, reactivity was consistently present in the 60-, 41-, 31-, and 22- or 24-kDa regions. Samples considered negative usually reacted to fewer than three bands, with reactivity usually being faint. A commercially available, rapid dot blot assay showed strong agreement with the majority standard.

Regeneration of immunosorbent surfaces used in clinical, industrial and environmental biosensors. Role of covalent and non-covalent interactions

The durability and regeneration of antibodies immobilized to commercial immunosorbents were investigated by monitoring Ag-Ab dissociation. Solutions consisting of 0.01 M hydrochloric acid (HCl), 10% propionic acid, 50% ethylene glycol and 10% SDS in 6 M urea were used in the evaluation of antigen dissociation from antibody covalently immobilized to glass and polystyrene beads, microtiter plates and Immobilon filters. RAH-IgG, used as a model antibody, bound strongly to all covalent surfaces. However, on adsorption to Nunc-1 microtiter plates, 25-60% of RAH-IgG was removed by all dissociating solutions. Covalent binding to Sanger beads was weakest relative to other covalent surfaces, exhibiting 30% and 65% detachment with ethylene glycol and SDS in urea, respectively. Although all four solutions dissociated antigen from surface-bound antibody, HCl and propionic acid were more effective on most surfaces. The antibody remained functional following antigen dissociation and reassociated to nearly 100% on all surfaces except Sanger beads and Nunc-1 microtiter plates. This study was initiated to evaluate regeneration and reuse of microelisa plates and emerging biosensors as a means of reducing routine laboratory analysis costs. Data are presented to demonstrate the reusability of microtiter plates in ELISAs following antigen dissociation from covalently bound antibody.

Blocking dot-ELISA, using a monoclonal antibody for detection of antibodies to bluetongue virus in bovine and ovine sera

A modified solid phase blocking enzyme immunosorbent assay (ELISA), using a monoclonal antibody (McAb) against the group specific bluetongue virus (BTV) antigen is described for detection of anti-BTV antibodies in cattle and sheep sera. Dots of an optimal dilution of BTV antigens were adsorbed to nitrocellulose (NC) paper (hence dot-ELISA) and then the remaining adsorptive sites were saturated with gelatin. After exposure to bovine or ovine test serum the NC strips were reacted with the McAb. The presence of McAb was detected with a peroxidase-conjugated anti-mouse IgG (H and L). In the absence of anti-BTV antibody in test sera, BTV antigen sites were reactive with McAb as indicated by a brown colored dot after enzyme degradation of hydrogen peroxide in the presence of diamino benzidine (DAB) or amino ethylcarbazole (AEC). In the presence of sufficient anti-BTV antibody no color reaction was observed. The blocking (B) dot-ELISA was superior to the agar gel immunodiffusion (AGID) in detecting anti-BTV antibodies in bovine and ovine sera early after experimental infection with BTV type 10. In 5 of 7 animals inoculated by combined intravenous and subcutaneous routes, anti-BTV antibodies in sera were detectable as early as 7 days post infection (DPI), all of which were AGID negative. Comparable B-dot-ELISA and AGID results were found in 23 paired sera (pre and 20 DPI) from cattle experimentally infected with different types of BTV and in 100 AGID negative sera from Ontario dairy and Alberta beef cattle.(ABSTRACT TRUNCATED AT 250 WORDS)

Cross-reactive antibodies to mycoplasmas found in human sera by the enzyme-linked immunosorbent assay (ELISA)

Antibodies against Mycoplasma pneumoniae in patients' sera with M. pneumoniae infection were measured by the complement fixation (CF) test and enzyme-linked immunosorbent assay (ELISA). Many patients' sera cross-reacted with heterologous mycoplasmal ELISA antigens such as M. hominis, M. hyorhinis, M. orale, M. pulmonis and M. salivarium. The sera with high CF (CF greater than or equal to 40) titers gave significantly higher ELISA values to M. hyorhinis (P less than 0.001) and M. pulmonis (P less than 0.001), which are not parasitic for humans, than those with low CF (CF less than 20) titer. Human normal immunoglobulin G (human normal IgG) containing 98% or more IgG, prepared from pooled plasma of at least 500 normal human donors, showed ELISA reactions with all mycoplasmal strains used. The nonspecific adsorption of human normal IgG on the surface of plate wells and on medium components which might contaminate mycoplasmal ELISA antigens could be disregarded. These results suggest that cross-reactive antibodies to mycoplasmas exist in human sera, and they affect the results of ELISA for serodiagnosis of M. pneumoniae infection.

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)

Adsorption-desorption of antigen to polystyrene plates used in ELISA

Since ELISA reliability depends to a great extent upon solid-phase reagent concentration and stability, we sought to analyse the influence of experimental conditions during ELISA performance on the adsorption/desorption of proteins to microplates. The effect upon desorption of several experimental parameters (antigen concentration, antibody concentration and affinity, washings, conjugate and inhibitor incubations) and quantitative treatment of protein-polystyrene adsorption were analysed. The adsorption to polystyrene microplates was studied with a hapten-conjugated protein (BSA-Ar36) in order to facilitate the analysis of the influence of antibody affinity on desorption during ELISA. Our results show that polystyrene plates adsorb BSA-Ar36 according to the Langmuir isotherm. The adsorption constant was 2.1 X 10(8) L/mol and maximal surface concentration of protein on solid phase was 1.8 X 10(-7) g/cm2. Although desorption was present, we observed that it did not affect the reliability of results of either direct or inhibition ELISA, because it was not dependent on the composition of the sample.

Dot-enzyme immunoassay for visual detection of antibodies to pseudorabies virus in swine serum

A modified solid-phase enzyme immunoassay (EIA) is described for the visual detection of anti-pseudorabies virus (anti-PRV) antibody in porcine serum. Dots of PRV antigens were adsorbed to nitrocellulose paper (hence the name dot-EIA), and the remaining nonspecifically reactive sites were blocked with bovine serum albumin or skim milk powder. After immersion in test serum, bound antibodies were reacted with a peroxidase-conjugated anti-porcine immunoglobulin G (H & L). Positive reactions were easily visualized as brown dots after enzyme degradation of a substrate containing hydrogen peroxide and diaminobenzidine. The dot-EIA was comparable to the serum neutralization test and the standard microtiter EIA in its ability to detect antibody in the sera of pigs 9 days after experimental infection and 12 days after contact with infected pigs. The sensitivity and specificity of the dot-EIA relative to the serum neutralization test and the standard EIA were determined from the testing of 856 field sera from the United Kingdom, the United States, and Canada. In all comparisons, both the relative sensitivity and specificity of the dot-EIA were in the order of 98 to 99%. The dot EIA appears to have potential application as a rapid and economical field test in the diagnosis of PRV infection.

Enzyme immunoassay: binding of Salmonella antigens to activated microtiter plates

A heat extract prepared from radiolabeled Salmonella cells was used to determine if covalent binding to activated surface of polystyrene plates would improve antigen retention thus contributing to increase sensitivity in an enzyme immunoassay for Salmonella antigen. The effect of treatment with ethylchloroformate on the retention of antigens passively absorbed to polyvinylchloride and polystyrene plates was also investigated. Chemically modified plates retained more radiolabeled antigens after washing than did untreated plates in which the antigens had been physically adsorbed. However, improvement of assay sensitivity depended on the type of plate used for covalent binding of antigen. N-succinimidyl 3-(2-pyridyldithio) propionate (SPDP), was found to be potentially useful for mediation of covalent binding of antigens to activated plates.

Rapid detection of salmonellae by immunoassays with titanous hydroxide as the solid phase

Radioimmunometric and enzyme-immunometric assays were developed for the detection of salmonellae in pure and mixed cultures as well as in 59 food samples. The performances of titanous hydroxide suspension and microtiter plates as the solid phase for the immobilization of microorganisms were compared in these immunoassays. Detection of populations of salmonella cells in pure culture, diluted with saline, was 4- to 10-fold more sensitive with the microtiter plates. However, with mixed culture of salmonella and other enterobacterial species, the detection sensitivity with titanous hydroxide was 100- to 160-fold more sensitive than with microtiter plates. Good correlation existed between results of a standard cultural method for the detection of salmonellae in foods and those obtained from radioimmunometric and enzyme-immunometric assays utilizing titanous hydroxide. However, a high incidence of false-positive and false-negative results with food samples occurred with the enzyme-immunometric assay utilizing microtiter plates. The results provided strong evidence for the merits of substituting titanous hydroxide for microtiter plates as the solid phase for the immobilization of salmonellae for their detection by immunoassays. The immunoassays were rapid and enabled the analysis of a large number of selective enrichment cultures of food samples for salmonellae within 8 h.

Performance testing of antigen-coated polystyrene microplates for ELISA measurements of serum antibodies to bacterial and dietary antigens

The adsorption of dietary antigens to polystyrene microplates was influenced by pH. Coating for 5 h at 37 degrees C followed by at least 18 h at 4 degrees C gave the best result with the six dietary and nine bacterial antigens tested in this study. Unwanted background activity was mainly caused by direct binding of human immunoglobulin in the second layer. This problem was mainly observed with coats based on antigens with relatively poor binding activity and could be reduced to an acceptable level by addition of 0.5% bovine serum albumin in the diluents. Microplates from various manufacturers showed large differences in antigen adsorbing properties and there were considerable variations among batches. Careful performance testing of microplates and selection of appropriate batches are therefore necessary.

Immobilized glycoconjugates for cell recognition studies

Specific cell-cell recognition and adhesion may involve cell surface glycoconjugates on one cell binding the complementary carbohydrate receptors on an apposing cell surface. Such interactions have been modeled by immobilizing simple synthetic glycosides, glycoproteins, glycosaminoglycans, and glycolipids on otherwise inert plastic surfaces and incubating them with intact cells. Using this approach, the ability of several cell types to recognize specific carbohydrates has been demonstrated. This carbohydrate-directed cell adhesion may depend on cell surface carbohydrate receptors which mediate both the initial specific adhesion and complex postrecognition cellular responses. While the relationship of the cell adhesion demonstrated here to cell-cell recognition in vivo has yet to be determined, this well-controlled biochemical approach may reveal new information on the way in which cells analyze and respond to their immediate external environment.

Polycarbonate-coated microsticks as solid-phase carriers in an enzyme-linked immunosorbent assay for rubella antibody

We evaluated the use of microsticks as solid-phase carriers in an enzyme-linked immunosorbent assay for rubella antibody. The microstick enzyme-linked immunosorbent assay was found to be equal in sensitivity to plate and disk enzyme-linked immunosorbent assays and presumably more sensitive than hemagglutination and immunofluorescence assays. The microstick as a solid-phase carrier offers advantages over both plate and bead carriers.