An investigation of the use of urease-antibody conjugates in enzyme immunoassays

Surface Chemistry Studies on the Formation of Mixed Stearic Acid/Phenylalanine Dehydrogenase Langmuir and Langmuir-Blodgett Films

This work investigates the physicochemical properties of mixed stearic acid (HSt)/phenylalanine dehydrogenase enzyme (PheDH) Langmuir films and their immobilization onto solid supports as Langmuir-Blodgett (LB) films. PheDH from the aqueous subphase enters the surfactant matrix up to an exclusion surface pressure of 25.3 mN/m, leading to the formation of stable and highly condensed mixed Langmuir monolayers. Hydrophobic interactions between the enzyme and HSt nonpolar groups tuned the secondary structure of PheDH, evidenced by the presence of β-sheet structures as demonstrated by infrared and circular dichroism spectra. The floating monolayers were successfully transferred to solid quartz supports, yielding Y-type LB films, and then characterized employing fluorescence, circular dichroism, and microscopic techniques, which indicated that PheDH was co-immobilized with HSt proportionally to the number of transferred layers. The enzyme fluidized the HSt monolayers, reducing their maximum dipoles when condensed to their maximum, and disorganized the alkyl chains of the fatty acid, as detected with infrared spectroscopy. The stability of the mixed floating monolayers enabled their transfer to solid supports as LB films, which is important for producing optical and electrochemical sensors for phenylalanine whose molecular architecture can be controlled with precision.

Carbon Nanotubes and Algal Polysaccharides To Enhance the Enzymatic Properties of Urease in Lipid Langmuir-Blodgett Films

Algal polysaccharides (extracellular polysaccharides) and carbon nanotubes (CNTs) were adsorbed on dioctadecyldimethylammonium bromide Langmuir monolayers to serve as a matrix for the incorporation of urease. The physicochemical properties of the supramolecular system as a monolayer at the air-water interface were investigated by surface pressure-area isotherms, surface potential-area isotherms, interfacial shear rheology, vibrational spectroscopy, and Brewster angle microscopy. The floating monolayers were transferred to hydrophilic solid supports, quartz, mica, or capacitive electrolyte-insulator-semiconductor (EIS) devices, through the Langmuir-Blodgett (LB) technique, forming mixed films, which were investigated by quartz crystal microbalance, fluorescence spectroscopy, and field emission gun scanning electron microscopy. The enzyme activity was studied with UV-vis spectroscopy, and the feasibility of the thin film as a urea sensor was essayed in an EIS sensor device. The presence of CNT in the enzyme-lipid LB film not only tuned the catalytic activity of urease but also helped to conserve its enzyme activity. Viability as a urease sensor was demonstrated with capacitance-voltage and constant capacitance measurements, exhibiting regular and distinctive output signals over all concentrations used in this work. These results are related to the synergism between the compounds on the active layer, leading to a surface morphology that allowed fast analyte diffusion owing to an adequate molecular accommodation, which also preserved the urease activity. This work demonstrates the feasibility of employing LB films composed of lipids, CNT, algal polysaccharides, and enzymes as EIS devices for biosensing applications.

16 Methods for Detecting Microbial Pathogens in Food and Water

Newly developed methods for the detection of bacteria and viruses have provided microbiologists with the means to rapidly identify and monitor specific microorganisms in food and water. Traditional methods of testing involve culture techniques to increase the numbers of the organism to a detectable level, followed by isolation and biochemical identification. This chapter focuses on the methodologies to detect pathogens and indicator organisms; however, the methods described are applicable to most bacteria. As detection and isolation methods have improved, a growing number of pathogens have been identified as important food- and waterborne pathogens. This chapter describes the use of nucleic acid and antibody probes that have the potential to circumvent the need to culture the organism prior to identification. Nucleic acid probes have become a valuable diagnostic reagent in the identification of human and animal pathogens and have made possible the identification of viruses and bacteria that are difficult, if not impossible, to cultivate. DNA probes have also proved to be a useful tool for identifying and monitoring the organisms in food and the environment.

Inhibition of soybean urease by triketone oximes

Competitive inhibition of soybean urease by 15 triketone oximes has been studied at 36 degrees C in aqueous solution (pH 4.95). The studied oximes are supposed chelators for the nickel atom in the urease metallocenter. The inhibition constants of urea hydrolysis (K(i)) varied in the range 2.7-248 microM depending on the oxime structure. Analysis of this dependency demonstrates that the optimal inhibitor is the one containing carbonyl group in position 1 of the cycle, the ethoxyimino group and alkyl residue in the substituent in position 2, as well as the methoxycarbonyl group in position 4 of the cycle.

Biocolloids with ordered urease multilayer shells as enzymatic reactors

The preparation of biocolloids with organized enzyme-containing multilayer shells for exploitation as colloidal enzymatic nanoreactors is described. Urease multilayers were assembled onto submicrometer-sized polystyrene spheres by the sequential adsorption of urease and polyelectrolyte, in a predetermined order, utilizing electrostatic interactions for layer growth. The catalytic activity of the biocolloids increased proportionally with the number of urease layers deposited on the particles, demonstrating that biocolloid particles with tailored enzymatic activities can be produced. It was further found that precoating the latex spheres with nanoparticles (40-nm silica or 12-nm magnetite) enhanced both the stability (with respect to adsorption) and enzymatic activity of the urease multilayers. The presence of the magnetite nanoparticle coating also provided a magnetic function that allowed the biocolloids to be easily and rapidly separated with a permanent magnet. The fabrication of such colloids opens new avenues for the application of bioparticles and represents a promising route for the creation of complex catalytic particles.

Amperometric immunosensors based on protein A coupled polyaniline-perfluorosulfonated ionomer composite electrodes

A very sensitive immunosensor based on polyaniline/ Nafion/protein A (PA/NF/PrA) composite electrodes has been developed for the amperometric immunoanalysis with urease-labeled immunoreagents. The use of urease conjugated goat anti-RIgG (GaRIgG-Ur) as the labeled antibody and urea as the substrate with an amperometric detection at -200 mV (vs Ag/AgCl) resulted in a dynamic range of 50-2000 ng mL-1 and a low detection limit of 10 ng/mL (64 pM) for the immunoanalysis of rabbit immunoglobulin G (RIgG). Because of the special affinity between protein A and RIgG, the PA/NF/PrA electrode can be regenerated repetitively by changing the pH of the buffer solutions. Characteristics of the PA/NF/PrA/RIgG immunosensor and optimal conditions for the competitive immunoanalysis of RIgG with FIA were studied.

Evaluation of a blocking ELISA using a urease conjugate for the detection of antibodies to pseudorabies virus

A blocking enzyme-linked immunosorbent assay (ELISA) using a urease conjugate (U-B-ELISA) was evaluated for screening sera for antibodies to pseudorabies virus under field conditions. A total of 764 serum samples were analyzed by U-B-ELISA. Of these, 264 were evaluated by both virus neutralization and U-B-ELISA, and the results were compared. U-B-ELISA showed 98.5% and 98.9% sensitivity and specificity, respectively. This test combines the sensitivity and specificity of the blocking ELISA format while allowing visual assessment of results.

Determination of optimal liquid medium for enzyme expression by Helicobacter pylori

AIMS

To determine the best medium for the growth and enzyme expression of Helicobacter pylori.

METHODS

Twelve H pylori isolates from histologically confirmed infected patients were cultured on Brucella broth (BB), Brucella broth minus bisulphite (BLBB), and brain-heart infusion broth (BHIB), all supplemented with 5% (v/v) fetal calf serum. Growth rates and enzyme expressions of all H pylori isolates cultivated in these media were evaluated.

RESULTS

Although both BLBB and BHIB supported good growth of H pylori under microaerophilic conditions, the total protein content of H pylori detected was much higher with BHIB cultivation. Measurement of the specific activities of urease, phospholipase C, and sphingomyelinase for 12 H pylori isolates cultivated in these media, showed that BHIB supported the highest expression of these enzymes. Although BLBB supported better growth of H pylori than BB, it did not increase enzyme expression.

CONCLUSIONS

Cultivation of H pylori in BHIB is recommended for studies on the physiology, metabolism, and enzyme expression of the organism.

Alterations in cardiac muscarinic acetylcholine receptors in mice with autoimmune myocarditis and association with circulating muscarinic receptor-related autoantibodies

Hearts from mice hyperimmunized with cardiac tissue were studied to evaluate the expression and biological activity of muscarinic cholinergic receptors and immunoglobulin G deposits along the immunization period. Mice were sacrificed at 10 day intervals from the first injection up to day 100. Simultaneously, the activity of autoantibodies against muscarinic receptors on normal hearts was also examined in sera. Hearts with autoimmune myocarditis showed a muscarinic receptor-related dysfunction, with an impaired response to exogenous muscarinic agonists and a significant reduction in muscarinic binding sites, both effects being maximum at 40-50 days post-immunization. In addition, serum or immunoglobulin G from mice with myocarditis were able to interact with muscarinic acetylcholine receptors displaying a partial agonist effect. Autoimmune sera and immunoglobulin G reduced heart contractility while inhibited 3H-QNB binding to cardiac acetylcholine receptors in a concentration dependent manner showing the highest effects at days 40-50 and decreased progressively thereafter. The development of muscarinic receptor-related cardiac dysfunction may be associated with the presence of circulating antibodies having muscarinic receptor activity. These studies are of relevance to clinical conditions such as Chagas' disease, where immunological processes involving the cholinergic system are considered to cause cardiomyopathy.

Anti-tumor antibody produced by human tumor-infiltrating and peripheral blood B lymphocytes

Cell suspensions from 69 human tumor biopsies and malignant effusions depleted of infiltrating T cells were incubated for 10-14 days with mitomycin-C-treated cells of the transformed T cell line MOT as feeder cells. B lymphocytes proliferated and differentiated as indicated by immunoglobulin (Ig) secretion in the culture supernatants (B cell expansion). Ig was present in culture supernatants of tumor cell suspensions incubated without MOT feeder cells (non-expanded cells), but the addition of MOT feeder cells to these cultures invariably resulted in a significant increase in Ig concentration. While IgG, IgA, and IgM isotypes were all detected in supernatants of both expanded- and non-expanded tumor cell suspensions, the increase in total Ig induced by MOT feeder cells was mainly due to an increase in IgG. Peripheral blood B lymphocytes (PBBL) from 15 cancer patients and 4 healthy individuals were also successfully expanded by the same method. In these it was shown that IgA was the predominant Ig isotype. Using a modified enzyme-linked immunosorbent assay, IgG of 25/36 expansions from tumor cell suspensions showed reactivity with autologous tumor targets, and that from 10/13 expansions reacted with allogeneic tumor targets of the same histological diagnosis. No reactivity was found against tumor targets of different histology. IgG of 4/10 expansions of PBBL from cancer patients showed reactivity with allogeneic tumor targets of the same histology, while no reactivity was demonstrated against tumor targets of different histology. IgG of expanded PBBL from healthy individuals showed no reactivity against tumor targets. This method allows detailed study of the specific humoral antitumor immune response of intratumoral and peripheral blood B lymphocytes in cancer.

Assessment of monoclonal antibodies to Echinococcus granulosus antigen 5 and antigen B for detection of human hydatid circulating antigens

Four monoclonal antibodies (MAb) to Echinococcus granulosus Antigen 5 (Ag5) and Antigen B (AgB) were assessed in an enzyme-linked immunosorbent assay (ELISA) for detection of circulating antigens (CAg) in sera of human patients with E. granulosus infection. Around 5.5-8% of 200 sera from 42 surgically proven hydatid patients contained detectable CAg by individual MAb. The combined detection rate for CAg, using four MAb, was 19% (38/200). Although hydatid CAg was detected by MAb in at least one serum sample from 21 of 42 patients, some patients remained negative in the assay regardless of the time when serum samples were taken (pre- or post-operatively), or of the continuing presence of hydatid cysts, their location or fertility. In addition, it was observed that the binding capacity of MAb for sheep hydatid cyst fluid antigen (SHCF) was somewhat reduced in the presence of normal human serum. The CAg detection assay would only be useful for assessment of hydatid infection status in patients with detectable CAg in serum samples.

Effect of antigen-specific T helper cells or interleukin-2 on suppressive ability of macrophage subsets detected in spleens of Trypanosoma cruzi-infected mice as determined by limiting dilution-partition analysis

Trypanosoma cruzi, a protozoan parasite and the causative agent of Chagas' disease, induces a state of lymphocyte hyporesponsiveness to both mitogenic and antigenic stimuli in mice during the acute phase of infection. Addition of spleen cells from T. cruzi-infected mice (SCinf) to microcultures of spleen cells from noninfected mice (SCn) suppresses the responsiveness of such cultures to antigenic challenge and to mitogenic stimulation. We analyzed the regulatory cell populations in SCinf by limiting dilution-partition analysis and found a complex regulatory circuit in T. cruzi-infected mice consisting of two suppressive macrophage subsets and an enhancing T-cell population. This T-cell population was able to abrogate or escape the suppressive ability of one suppressor macrophage subset, yet was suppressed by the other macrophage subset. To further study the cellular interactions of this regulatory circuit and analyze the suppressive abilities of the two suppressor macrophage subsets, we examined the effect of adding either primed T helper cells of known specificity or interleukin-2 to the limiting dilution-partition analysis microcultures. The results of these experiments suggest that one suppressor macrophage subset, which is abundant and, therefore, detected with low doses of SCinf, is able to suppress both mitogen- and primary antigen-specific responses but is unable to inhibit cells once they are already activated or primed. The other macrophage subset, which is presumably a less abundant or less active population (since high doses of SCinf are required to detect it), is able to suppress the response of activated or primed T cells by the inhibition of interleukin-2 production.

Evaluation of a monoclonal antibody-based competition ELISA for the diagnosis of human hydatidosis

An antibody competition enzyme-linked immunosorbent assay (ELISA) using 4 different monoclonal antibodies (MAb) raised against major antigens (Antigen 5 and Antigen B) of Echinococcus granulosus was evaluated for the diagnosis of human hydatidosis. The competition assay, using anti-Ag5 MAb 24.14, detected specific antibodies in 70% (131/188) of sera from patients with surgically confirmed E. granulosus infection and 38.5% (10/26) of sera from patients with E. multilocularis infection. None of the sera from patients with Taenia solium cysticercosis (10), T. saginata (2), filariasis (22), strongyloidiasis (19), fascioliasis (4), bilharziasis (4) and amoebiasis (2) tested were positive using a cut-off point established through reaction between MAb 24.14 and normal human sera. The combined use of the MAb 24.14-based competition ELISA with the conventional antibody-binding assay provides a highly sensitive (92.8%) and specific screening system for human hydatid disease diagnosis.

Macrophage regulation of immune responses of spleen cells from mice infected with Trypanosoma cruzi

Mice infected with the protozoan parasite, Trypanosoma cruzi, are known to be immunosuppressed in responsiveness to heterologous antigens and parasite-specific antigens. This suppression is mediated by suppressor macrophages and is exemplified by deficient T cell activity and abnormal cytokine production. Neither the mechanism by which suppressor macrophages effect suppression nor the characteristics of these suppressor macrophages is known. In the present study, we analyzed the regulatory cell populations in splenocytes of infected mice (SCinf) and their interactions by limiting dilution-partition analysis, an approach which allows the functional separation of multiple regulatory cell subpopulations within cell mixtures. Our results demonstrate the presence of a complex immunoregulatory circuit in SCinf affecting the generation of anti-sheep erythrocyte antibody responses in vitro. Titration of SCinf (but not peritoneal exudate or lymph node cells) into Mishell-Dutton microcultures of normal spleen cells generated complex dose-response curves with two zones of suppressed responses following the addition of either low or high doses of SCinf to the cultures. Addition of intermediate doses of SCinf to the microcultures restored responsiveness. Both the low- and high-dose zones of suppression were shown to be mediated by macrophages, whereas T cells were responsible for the restored responsiveness at intermediate doses of SCinf. Examination of the development of this complex regulatory pattern during the course of the acute phase of infection indicated the sequential development of one suppressor macrophage population, followed by the development of the beneficial T cell population, and finally the expression of the second suppressive macrophage population.

Structure function analysis of the H-2 Abp gene

The gene encoding the H-2 Ap class II beta chain was isolated from a B10.P genomic library and sequenced. This gene was also used to construct transfectants of the CH12 lymphoma clone CH12.LX, which express the Abp gene product in association with the endogenous A alpha k chain. We present here the first report of the complete nucleotide coding sequence of Abp. The predicted amino acid sequence of Abp reveals only five residues different from Abq, four of which are present in the mature peptide. These four amino acid changes could account for the differential susceptibility of H-2q vs H-2p mice to the development of collagen-induced arthritis (CIA). Antibodies specific for the transfected Abp protein induce CH12.LX cells to secrete immunoglobulin in the presence of antigen. Comparison of the amino acid sequence with other A beta chains that have been tested in signal transduction experiments suggests that amino acid 9 may be important to the signaling ability of class II A molecules.

The influence of maternal antibody and age of calves on effective vaccination against Leptospira interrogans serovar hardjo

Twelve seronegative cows were vaccinated with an experimental bivalent Leptospira interrogans serovars hardjo and pomona vaccine late in their first pregnancy. Calves born of these dams were divided into 4 equal groups that received this vaccine at 4, 6, 10 and 18 weeks of age, respectively. Before vaccination the group geometric mean titres of maternally-derived circulating antibodies ranged from 2 to 25 for the microscopic agglutination (MA) test and 3 to 35 for enzyme-linked immunosorbent assay (ELISA) using a serovar hardjo outer envelope antigen. Post-vaccination peak titres were 645 to 1612 for MA and 562 to 1037 for ELISA, respectively. Calves vaccinated at the youngest age, had the highest pre-vaccination circulating maternal antibody titres, but showed the smallest rise in post-vaccination antibody titres. Circulating maternal antibody was detected in calves up to 13 weeks of age. All immunised calves were protected against a virulent challenge with serovar hardjo type Hardjobovis, regardless of their age or maternally-derived antibody titres. These findings indicate that calves as young as 4 weeks old, vaccinated in the presence of maternally-derived antibody, can be fully protected against homologous virulent challenge.

Description of a urease-based microELISA for the analysis of limiting dilution microcultures

Limiting dilution analysis has been a valuable approach for both determining the frequency of cell subpopulations elicited during immune responses, as well as for the analysis of immunoregulatory circuits. We describe a simple, visually scored spot test for evaluating the response of Mishell-Dutton microcultures used in limiting dilution analysis. This spot test is based on a microELISA using immunoreagents conjugated to the enzyme, urease, as an alternative to the hemolytic spot test. The assay as performed in Terasaki trays requires minute quantities (less than 10 microliters) of culture supernatant, yet the ELISA yields a distinct color difference between tray wells containing culture supernatants derived from responding (purple) and nonresponding (yellow) microcultures. Although designed to be scored rapidly by visual inspection, the assay can be quantified by manual alignment of the Terasaki tray wells on commercially available ELISA plate readers with an accuracy and reproducibility comparable to assays performed in 96-well ELISA plates. Determination of anti-sheep RBC responses in limiting dilution Mishell-Dutton microcultures with both the hemolytic spot test and the urease-microELISA spot test showed a very close correlation between the results of the two assays. However, the urease-microELISA should be amenable for use with antigens not readily conjugated to an indicator RBC, and should be useful in those situations where determination of the antibody subclass(es) produced by responding microcultures is desired.

Contribution of a 28-kilodalton membrane protein to the virulence of Haemophilus influenzae

A Haemophilus influenzae b (Hib) membrane protein with a molecular mass of 28 kDa bound polyclonal antisera raised against a highly purified Hib fimbrial subunit. We cloned the gene encoding this protein and found that the gene was expressed in Escherichia coli. DNA sequence analysis identified an 843-bp open reading frame which predicted a 26.78-kDa protein with an amino-terminal signal sequence and a mature protein with 70% similarity to the 28-kDa lipoprotein of E. coli (F. Yu, S. Inouye, and M. Inouye, J. Biol. Chem. 261:2284, 1986). Colony blot hybridization analysis with an intergenic probe of the cloned gene demonstrated that 29 of 32 H. influenzae strains hybridize with this gene. Insertion of a chloramphenicol acetyltransferase gene into the open reading frame inactivated expression of the 28-kDa protein in E. coli. Isogenic Hib strains were derived by marker exchange mutagenesis to generate mutants which no longer expressed the 28-kDa protein as recognized with Western immunoblot analysis. There was no difference in the rate of nasopharyngeal colonization of infant rats or monkeys by the isogenic mutants which lacked the 28-kDa protein compared with colonization by the wild-type strain. In contrast, the frequency of invasion and density of bacteremia in infant rats caused by the isogenic mutants were reduced relative to those caused by the wild-type Hib strain. We conclude that this 28-kDa outer membrane protein aids transepithelial invasion of type b strains but is not essential.

Detection of total DNA with single-stranded DNA binding protein conjugates

We have developed a rapid and sensitive method for total DNA measurement using single-stranded DNA binding protein from E coli conjugated with horseradish peroxidase or urease. To detect DNA, the sample is heated or alkali treated to denature the DNA and then filtered through nylon or nitrocellulose membranes. After the single-stranded DNA is bound to the membrane, single-stranded DNA binding protein enzyme-conjugate is incubated with the membrane. Next, the unbound conjugate is washed off the membrane and the bound conjugate detected colorimetrically. The assay can detect 10 pg of DNA in less than 3 hr. This method can be applied to the detection of DNA contamination in therapeutic proteins produced by recombinant DNA or hybridoma techniques.

Visuwell Reagin, a non-treponemal enzyme-linked immunosorbent assay for the serodiagnosis of syphilis

A urease-based enzyme-linked immunosorbent assay (ELISA) has been developed for the detection of reagin antibodies in serum. Visuwell Reagin (ADI Diagnostics Inc., Rexdale, Ontario, Canada) is a non-treponemal screening test for the serodiagnosis of syphilis which has the benefits of large batch testing, automatability, and objective interpretation of results. Unheated, undiluted sera are incubated in 96-well microtiter plates coated with a modified cardiolipin-lecithin-cholesterol antigen. Antibody bound to the plate is detected by an anti-human immunoglobulin G-urease conjugate. The procedure consists of three steps, with a total test time of 60 min. Visuwell Reagin ELISA was compared with the Venereal Disease Research Laboratory (VDRL) test and the reagin screening test (RST) with the following results. For ELISA versus the VDRL test, the sensitivities for untreated syphilis (n = 37) were 97.3% for both ELISA and the VDRL test, the confirmatory positive values (n = 79) were 84.8% for ELISA and 72.2% for the VDRL test, and the specificities for normal samples (n = 1,327) were 98.8% for ELISA and 99.5% for the VDRL test. For ELISA versus RST, the sensitivities for untreated syphilis (n = 57) were 94.7% for ELISA and 87.7% for RST, the confirmatory positive values (n = 26) were 96.2% for ELISA and 92.3% for RST, and the specificities for normal samples (n = 1,891) were 99.6% for ELISA and 99.3% for RST. The overall concordance values of ELISA with VDRL test and RST were 96.7 and 97.9%, respectively. The specificity of ELISA compared with that of RST may be underestimated, since confirmatory data were not available for all apparent false-positive samples. Visuwell Reagin had increased sensitivity and similar specificity compared with flocculation tests.

A simple hemagglutination method for the detection of cell surface antigens

A rapid, easy and reproducible hemagglutination method is described for the detection of cell surface antigens. This method can be used for the determination of cell subpopulations and the screening of monoclonal antibody-secreting hybridomas. Fresh or paraformaldehyde-fixed cells, which have previously been labeled with an appropriate monoclonal antibody (of known or unknown specificity), are reacted with human erythrocytes coupled with the second antibody (rabbit anti-mouse immunoglobulins), in a round bottomed 96-well microtiter plate. The presence of specific agglutination and the end-point of serial dilutions of the labeled cells with unlabeled ones give an approximate estimation of the percentage of cells reacting with the monoclonal antibody under examination. The hemagglutination results correlate well with the results obtained using a conventional immunofluorescence method.

Evaluation of a serological test system for the diagnosis of natural Echinococcus granulosus infection in dogs using E. granulosus protoscolex and oncosphere antigens

Serum antibody responses in feral or domesticated dogs naturally infected with Echinococcus granulosus or/and other common helminths were examined in an enzyme-linked immunosorbent assay (ELISA) using antigens prepared from E. granulosus protoscoleces or oncospheres. The ELISA using the protoscolex antigen was optimised with serums from experimental dogs monospecifically infected with E. granulosus or other helminth parasites, and helminth-free dogs. Anti-protoscolex antibody was detected in 16 of 22 (72.7%) serums from feral dogs with E. granulosus burdens ranging from 300 to 302,600 worms per dog. Seven serums from feral dogs which did not harbour E. granulosus at autopsy but which originated from an endemic hydatid region were tested using protoscolex antigen, and 1 serum gave a positive reaction. One hundred and two serums from dogs known never to have been infected with E. granulosus all gave negative reactions to protoscolex antigen. The sensitivity of the ELISA test proved to be superior to that which has been achieved by arecoline purging as a method of diagnosis for E. granulosus infection in dogs. For use of the assay in hydatid control or eradication campaigns, its sensitivity can be increased by choosing a lower absorbance discrimination value above which serums are regarded as having positive reactions. However, this does introduce positive reactions of some serums from dogs infected with helminths other than E. granulosus. In further development of the assay, use of defined recombinant antigens may improve both sensitivity and specificity.(ABSTRACT TRUNCATED AT 250 WORDS)

An assessment of urease-based enzyme-linked immunosorbent assay

The use of urease in enzyme-linked immunosorbent assays (ELISAs) offers the advantages of convenience and safety. However, urease-based ELISA, performed in standard microtitre format, could result in false positive reactions upon prolonged incubation. False positive reactions appeared when wells containing substrate solution absorbed ammonia liberated from a reactive well nearby. Thus, the intensity of the false reaction was proportional to that of the urease reaction. The transfer of ammonia was demonstrated by pyrolysis-mass spectrometry. When urease conjugates were compared with peroxidase conjugates in the detection of IgG and IgM, there was no evidence that one enzyme was superior to the other in terms of increasing the sensitivity or the speed of ELISA.

Development of urease conjugated enzyme-linked immunosorbent assays (ELISA) for the detection of IgM and IgG antibodies against Mycoplasma pneumoniae in human sera

Urease conjugated enzyme linked immunosorbent assays (ELISA) were developed for the detection of human IgM and IgG antibodies against Mycoplasma pneumoniae. Results obtained by ELISA were compared with complement fixation test (CFT); which showed that of the 214 serum specimens tested, 80 were found to have antibody against M. pneumoniae. ELISA revealed that 70 of these specimens were IgG antibody, and 27 of them also contain IgM antibody. CFT failed to detect the presence of antibody against M. pneumoniae in five serum specimens tested. However, by using ELISA, three of them were found to have IgG and IgM antibodies. and the other two sera have IgG antibody only. Four out of the five specimens tested were the first serum specimens collected from patients with clinical and serological evidence of M. pneumoniae infection. In addition, 28 serum specimens, including 10 sera containing IgM rheumatoid factors and sera known to contain IgM antibody to other infectious organisms, were also tested for IgM antibody against M. pneumoniae by ELISA. None of these specimens showed a nonspecific reaction. ELISA had a sensitivity of 87.5% and a specificity of 96.3% when compared with CFT. Thus, ELISA developed in our laboratory is a specific test, and the results indicated that IgM ELISA might be used as a rapid diagnosis for M. pneumoniae infection.

Direct microculture enzyme-linked immunosorbent assay for studying neural cells: oligodendrocytes

Oligodendrocyte development has been studied in a standardized primary microculture system initiated from day 20-21 fetal rat brain using a solid-phase enzyme-linked immunosorbent assay (ELISA) carried out directly on fixed cells (direct microculture ELISA). A highly reproducible dissociation procedure is described that allows careful control of the number of cells seeded per culture. At a seeding density of 1 x 10(5) cells/culture, up to 250 oligodendrocyte-generating microcultures consisting of 10-12% oligodendrocytes can be prepared from a single fetal rat brain, thereby permitting the simultaneous assay of multiple developmental parameters in sibling cultures. The validity of this method for quantifying myelinogenesis was established by comparing the results obtained by direct microculture ELISA with immunocytochemical counting of cells in parallel cultures. As few as 200 oligodendrocytes could be detected using a biotinylated anti-Ig and an avidin-urease conjugate detection system; CNP immunoreactivity measured by ELISA was linearly proportional to the number of immunolabeled cells between 6 and 34 days in culture; the developmental time courses of 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP) and myelin basic protein (MBP) expression determined by the two methods were very similar. Finally, cell suspensions were seeded at increasing dilution to determine the number of cells required to generate cultures that tested positive for oligodendrocytes by ELISA. As few as 9,000 cells were sufficient, predicting a minimum of 8,000 oligoprogenitors per 20-21 day fetal rat brain. The application of direct microculture ELISA for studying oligodendrocyte population size and myelinogenesis is discussed.

A comparative assessment of four serological methods used in the detection and measurement of anti-parasite antibodies in the serum of the amphibian, bufo viridis

Antibodies against Crithidia fasciculata choanomastigotes were detected in green toad (Bufo viridis) sera by direct agglutination, indirect haemagglutination (IHA), complement-fixation test (CFT) and enzyme-linked immunosorbent assay (ELISA), Correlation coefficients (r) were calculated for comparisons between each of the techniques and regression formulae derived in order to convert antibody levels as determined by one immunological method to that of another. The highest mean titre obtained by ELISA was approximately 1.5–3.5 times greater than those obtained by the other techniques whilst CFT gave the lowest values. IHA and ELISA titres were affected by different preparations of the crithidial antigen extracts. Highly significant r values were determined for control sera when IHA was compared to ELISA (r > 0.79), and to both CFT and ELISA with immune animals (r > 0.96). ELISA would seem most applicable for screening other lower vertebrates for anti-parasite antibodies especially in areas of human disease prevalence.

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.

The primary immune response of the green toad (Bufo viridis) to challenge with Crithidia fasciculata

The primary immune response of the green toad (Bufo viridis) following immunization with Crithidia fasciculata choanomastigotes was studied. Lysins, agglutinins, and antibodies detectable by enzyme-linked immunosorbent assay (ELISA) were first detected in the sera of immunized animals one week after injection. The antibody titers increased to significant levels (P less than 0.01) and maximum values were reached seven weeks post-immunization. The stimulated immunoglobulins were antigen-specific, partially heat-labile, sensitive to the reducing agent dithiothreitol, possessed precipitin activity, effectively fixed complement and exhibited an electrophoretic mobility similar to the gamma-globulins of human serum. On this basis, it is probable that the antibody produced during the primary response in green toads is high molecular weight IgM. Increases in serum lysozyme levels paralleled the rise of antibody titers. Overall, the lysozyme concentration increased two-fold compared to the appropriate controls. This is the first report of the immune response in amphibians to experimental injection with protozoan parasites and the use of the ELISA technique to detect antibodies in amphibian sera.

A rapid quantitative capillary tube enzyme immunoassay for human chorionic gonadotropin in urine

A quantitative capillary tube enzyme immunoassay (CTEIA) method for the determination of human urinary chorionic gonadotropin (hCG) has been developed. The method utilizes an antibody-coated capillary tube through which the test fluid is passed and a urease-labelled second antibody in an immunometric format. Any hCG in the test solution is 'captured' by the immobilized antibody which is hybridoma derived and specific for the beta-subunit of hCG. The second hCG-specific antibody, conjugated to the enzyme urease, is used to detect the captured hCG on the internal surface of the capillary tube. The amount of urease bound to the surface is determined by the introduction of a substrate solution containing urea and the pH indicator bromothymol blue. The rate of colour change, from yellow to blue, caused by the release of ammonia from urea by urease, is determined in a spectrophotometer using a cell holder adapted to accommodate capillary tubes. The initial rate of absorbance change is directly proportional to the concentration of hCG in the sample in the range 0-100 mIU/ml. The test can detect concentrations of hCG as low as 10 mIU/ml in a total elapsed time of 5 min.

Inactivation of poliovirus with beta-propiolactone

The recovery of poliovirus D-antigen after virus inactivation was studied for two inactivating agents (beta-propiolactone and formalin) using the three poliovirus types (Sabin types 1, 2 and 3). With beta-propiolactone (BPL), D-antigen recoveries were high (88, 88 and 60%, respectively) but were significantly less when formalin was used (22, 15 and 25%). beta-Propiolactone inactivated virus was purified, combined with Freund's adjuvant and used to hyperimmunize rabbits. High titres (50 000-200 000) of specific neutralizing antibody were obtained.

Development of a monoclonal antibody for use in radioimmunoassay of ethynylestradiol

Production of monoclonal antibodies (MABs) to a 17 alpha-ethynyl-1,3,5 (10)-estratriene-3,17 beta-diol (ethynylestradiol, EE2) hapten is described. Culture antibodies generated by hybridized cells tested in enzyme-linked immunosorbent assay (ELISA) bound the 6-oxoethynyl-estradiol-6-(0-carboxymethyl) oxime-bovine serum albumin conjugate (EE2-6-0 CMO-BSA) but not BSA. On radioimmunoassay (RIA) with tritiated ethynylestradiol (3H-EE2), some of the antibodies demonstrated high binding affinity (Ka = 2.8 X 10(10) M-1) to EE2. Estradiol-17 beta, estrone and estriol did not show any displacement of 3H-EE2 from the MABs even at high concentration (1 X 10(4) ng/mL). Among the widely used progestins, norethynodrel and norethisterone exhibited considerable cross-reactivity (25.7-100% and 0.3-54.1%, respectively) but not levonor-gestrel with the MABs. The high affinity demonstrated by the MABs to EE2 3-sulfate but not to EE2 17-sulfate and EE2 3,17-disulfate suggests the dominant role of the 17 beta-hydroxyl group in immunogenicity.