The preparation of latex particles with covalently bound polyamines, IgG and measles agglutinins and their use in visual agglutination tests

Surface Modification of Polystyrene with Boronic Acid for Immunoaffinity-Based Cell Enrichment

Obtaining an enriched and phenotypically pure cell population from heterogeneous cell mixtures is important for diagnostics and biosensing. Existing techniques such as fluorescent-activated cell sorting (FACS) and magnetic-activated cell sorting (MACS) require preincubation with antibodies (Ab) and specialized equipment. Cell immunopanning removes the need for preincubation and can be done with no specialized equipment. The majority of the available antibody-mediated analyte capture techniques require a modification to the Abs for binding. In this work, no antibody modification is used because we take advantage of the carbohydrate chain in the Fc region of Ab. We use boronic acid as a cross-linker to bind the Ab to a modified surface. The process allows for functional orientation and cleavable binding of the Ab. In this study, we created an immunoaffinity matrix on polystyrene (PS), an inexpensive and ubiquitous plastic. We observed a 37% increase in Ab binding compared with that of a passive adsorption approach. The method also displayed a more consistent antibody binding with 17 times less variation in Ab loading among replicates than did the passive adsorption approach. Surface topography analysis revealed that a dextran coating reduced nonspecific antibody binding. Elemental analysis (XPS) was used to characterize the surface at different stages and showed that APBA molecules can bind upside-down on the surface. While upside-down antibodies likely remain functional, their elution behavior might differ from those bound in the desired way. Cell capture experiments show that the new surface has 43% better selectivity and 2.4-fold higher capture efficiency compared to a control surface of passively adsorbed Abs. This specific surface chemistry modification will allow the targeted capture of cells or analytes with the option of chemical detachment for further research and characterization.

Metal Nanoparticle and Quantum Dot Tags for Signal Amplification in Electrochemical Immunosensors for Biomarker Detection

With the increasing importance of healthcare and clinical diagnosis, as well as the growing demand for highly sensitive analytical instruments, immunosensors have received considerable attention. In this review, electrochemical immunosensor signal amplification strategies using metal nanoparticles (MNPs) and quantum dots (Qdots) as tags are overviewed, focusing on recent developments in the ultrasensitive detection of biomarkers. MNPs and Qdots can be used separately or in combination with other nanostructures, while performing the function of nanocarriers, electroactive labels, or catalysts. Thus, different functions of MNPs and Qdots as well as recent advances in electrochemical signal amplification are discussed. Additionally, the methods most often used for antibody immobilization on nanoparticles, immunoassay formats, and electrochemical methods for indirect biomarker detection are overviewed.

Site-directed antibody immobilization techniques for immunosensors

Immunosensor sensitivity, regenerability, and stability directly depend on the type of antibodies used for the immunosensor design, quantity of immobilized molecules, remaining activity upon immobilization, and proper orientation on the sensing interface. Although sensor surfaces prepared with antibodies immobilized in a random manner yield satisfactory results, site-directed immobilization of the sensing molecules significantly improves the immunosensor sensitivity, especially when planar supports are employed. This review focuses on the three most conventional site-directed antibody immobilization techniques used in immunosensor design. One strategy of immobilizing antibodies on the sensor surface is via affinity interactions with a pre-formed layer of the Fc binding proteins, e.g., protein A, protein G, Fc region specific antibodies or various recombinant proteins. Another immobilization strategy is based on the use of chemically or genetically engineered antibody fragments that can be attached to the sensor surface covered in gold or self-assembled monolayer via the sulfhydryl groups present in the hinge region. The third most common strategy is antibody immobilization via an oxidized oligosaccharide moiety present in the Fc region of the antibody. The principles, advantages, applications, and arising problems of these most often applied immobilization techniques are reviewed.

Development of latex agglutination test with recombinant NcSAG1 for the rapid detection of antibodies to Neospora caninum in cattle

Neospora caninum, an apicomplexan protozoan parasite, is recognized as a major cause of abortion in cattle. Surface antigen 1 of N. caninum (NcSAG1) is an important immunodominant candidate for the development of a diagnostic reagent for neosporosis. The present study describes the development and evaluation of a latex agglutination test (LAT) with recombinant NcSAG1 (rNcSAG1) for the detection of antibodies to N. caninum in cattle. The rNcSAG1 gene was cloned in pET-28a and protein was expressed in Escherichia coli BL21 (DE3). Carboxylated latex particles were coated with rNcSAG1 and the degree of agreement between LAT and a commercial enzyme-linked immunosorbent assay (iscomELISA) was evaluated by using of 164 serum samples. Twenty-two (13.4%) and 23 (14.0%) of samples were positive for antibodies to N. caninum by LAT and ELISA respectively. Eighteen of 23 ELISA-positive samples were positive according to the LAT and a substantial agreement (κ=0.77) was found between the results of LAT and ELISA. The results indicated that the LAT with rNcSAG1 would be a rapid, simple, relatively inexpensive and suitable diagnostic test for detection of specific antibodies in N. caninum infection under field conditions. Improvement in purification of rNcSAG1 can reduce probable false positive reactions and so increase the degree of agreement between the LAT and ELISA.

The relative roles of collagen adhesive receptor DDR2 activation and matrix stiffness on the downregulation of focal adhesion kinase in vascular smooth muscle cells

Cells within tissues derive mechanical anchorage and specific molecular signals from the insoluble extracellular matrix (ECM) that surrounds them. Understanding the role of different cues that extracellular matrices provide cells is critical for controlling and predicting cell response to scaffolding materials. Using an engineered extracellular matrix of Type I collagen we examined how the stiffness, supramolecular structure, and glycosylation of collagen matrices influence the protein levels of cellular FAK and the activation of myosin II. Our results show that (1) cellular FAK is downregulated on collagen fibrils, but not on a non-fibrillar monolayer of collagen, (2) the downregulation of FAK is independent of the stiffness of the collagen fibrils, and (3) FAK levels are correlated with levels of tyrosine phosphorylation of the collagen adhesion receptor DDR2. Further, siRNA depletion of DDR2 blocks FAK downregulation. Our results suggest that the collagen receptor DDR2 is involved in the regulation of FAK levels in vSMC adhered to Type I collagen matrices, and that regulation of FAK levels in these cells appears to be independent of matrix stiffness.

Latex of immunodiagnosis for detecting the Chagas disease. I. Synthesis of the base carboxylated latex

This article investigates the synthesis of two (monodisperse, carboxylated, and core-shell) latexes, through a batch and a semibatch emulsion copolymerizations of styrene (St) and methacrylic acid (MAA) onto polystyrene latex seeds. A mathematical model of the process was developed that predicts conversion, average particle size, and surface density of carboxyl groups. The model was adjusted to the batch reaction measurements, and then it was used in the design of the semibatch experiment. The semibatch reaction involved an initial homopolymerization of St followed by instantaneous addition of MAA-St-initiator. Compared with the batch reaction results, the semibatch policy more than doubled the surface density of carboxyl groups. The second part of this series describes the development of an immunodiagnosis latex-protein complex for detecting the Chagas disease, by coupling an antigen of Trypanosoma cruzi onto the produced carboxylated latexes.

Binding of TmHU to Single dsDNA as Observed by Optical Tweezers

Optical tweezers are employed to study the action of the histone-like protein from Thermotoga maritima (TmHU) on DNA at a single molecule level. Binding and disruption of TmHU to and from DNA are found to take place in discrete steps of 4-5 nm length and a net binding enthalpy of about 16kBT. This is in reasonable agreement with a microscopic model that estimates the extension of the binding sites of the protein and evaluates the energetics mainly for bending of the DNA in the course of interaction.

The elastic properties of single double-stranded DNA chains of different lengths as measured with optical tweezers

Optical tweezers are microscopic tools with extraordinary precision in the determination of the position (±2 nm) of a colloid (diameter: ∼2.0 μm) in 3D-space and in the measurement of small forces in the range between 0.1 and 100 pN (pN=10^-12 N). Experiments are reported in which single double-stranded (ds)-DNA chains of different length [2,000 base pairs (bp), 3,000, 4,000, and 6,000 bp] are spanned between two colloidal particles by use of appropriate molecular linkers. For the forces applied (≤40 pN) a fully reversible and well reproducible force-extension dependence is found. The data can be well described by both the worm-like chain model or by an approach developed by R. G. Winkler. For the resulting persistence length, a pronounced dependence on the ionic concentration in the surrounding medium is found.

Ultrasensitive detection of biomolecules with fluorescent dye-doped nanoparticles

Fluorescent-labeled molecules have been used extensively for a wide range of applications in biological detection and diagnosis. A new form of highly luminescent and photostable nanoparticles was generated by doping the fluorescent dye tris(2'2-bipyridyl)dichlororuthenium(II)hexahydrate (Rubpy) inside silica material. Because thousands of fluorescent dye molecules are encapsulated in the silica matrix that also serves to protect Rubpy dye from photodamaging oxidation, the Rubpy-dye-doped nanoparticles are extremely bright and photostable. We have used these nanoparticles successfully in various fluorescence labeling techniques, including fluorescent-linked immunosorbent assay, immunocytochemistry, immunohistochemistry, DNA microarray, and protein microarray. By combining the high-intensity luminescent nanoparticles with the specificity of antibody-mediated recognition, ultrasensitive target detection has been achieved. In all cases, assay results clearly demonstrated the superiority of the nanoparticles over organic fluorescent dye molecules and quantum dots in probe labeling for sensitive target detection. These results demonstrate the potential to apply these newly developed fluorescent nanoparticles in various biodetection systems.

Candida albicans cell wall antigens for serological diagnosis of candidemia

Serological tests for diagnosis of disseminated fungal infections in the immunocompromised host are used with varying results. In the present study, the relative ability of antibodies to specifically recognize Candida albicans cell wall components was evaluated in order to find antigenic markers for serological diagnosis of candidemia. Native C. albicans cell wall fragments (CW), periodate- (CWIO4) and proteinase-K- (CWP) treated CW, a mildly extracted phosphopeptidomannan (PPM), and beta(1-3)(1-6)-glucan were used as antigens in ELISA with sera from rabbits immunized with C. albicans (n = 10), patients with culture proven candidemia (n = 8) and healthy individuals (n = 8). The antibody response in rabbits consisted predominantly of anti-PPM antibodies, a finding that was substantiated by inhibition-ELISA. Consistently, periodate treatment (CW104) destroyed a major proportion of the antigenic epitopes. Low rabbit antibody levels were found against glucan, the major Candida cell wall component. These results supported the conclusion that glucan is localized mainly in the inner part of the C. albicans cell wall. In contrast to rabbits' serum IgG antibody response against PPM, which was at least tenfold higher than that raised against CW, patients with candidemia had similar IgG antibody levels against both antigens. These levels were significantly higher than those seen in healthy controls (CW, P = 0.0005 and PPM, P < 0.0001). Although the human anti-glucan and anti-CWIO4 IgG antibody levels were low overall, they were nonetheless significantly increased in the patient group (P = 0.0159 for antiglucan and P = 0.0491 for anti-CWIO4). In addition, a correlation was noticed between levels of these antibodies. No significant differences were found between patients and controls for IgM antibodies when CW, CWIO4, PPM and Glu were used as antigens. In conclusion, IgG antibodies to PPM and native cell wall fragments (CW) were highly discriminatory for recognition of candidemia and these antigens are thus promising candidates for use in serodiagnosis.

Homogeneous luminescence decay time-based assay using energy transfer from nanospheres

Following a study on the feasibility of resonance energy transfer (RET) from carboxylated nanospheres with an incorporated phosphorescent donor to a cationic polyelectrolyte/acceptor aggregate on their surface, a novel scheme for homogeneous assays is presented that is based on RET from phosphorescent biotinylated nanospheres to fluorescently labeled streptavidin (SA). The phosphorescent nanospheres, with a diameter of well below 50 nm, are made from carboxylated polyacrylonitrile and dyed with ruthenium(II)-tris-4,7-diphenyl-1,10-phenanthroline dichloride (Ru(dpp)). Due to the small size of the nanospheres and the complete extraction of the ruthenium dye into the nanospheres during the precipitation process, RET occurs from Ru(dpp) to the label if labeled SA binds to the surface of the nanospheres. Luminescence quenching by oxygen or other species present in the sample can be neglected due to the shielding effect of the polymer matrix. Based on this finding, a competitive binding assay was established, where avidin and labeled SA compete for the biotin binding sites on the nanosphere. The process of binding to the surface can be detected by measurement of the luminescence intensity or the apparent decay time which is in the order of 2.5-4.5 micros.

Development of rapid one-step immunochromatographic assay

An analytical system for a one-step immunoassay has been constructed using the concept of immunochromatography. The system employed two different antibodies that bound distinct epitopes of an analyte molecule: an antibody labeled with a signal generator (e.g., colloidal gold), which was placed in the dry state at a predetermined site on a glass-fiber membrane, and another antibody immobilized on the surface of a nitrocellulose membrane. Three membranes, one with the tracer, one with immobilized antibody, and a cellulose membrane as the absorbent of medium (in a sequence from the bottom), were attached to a plastic film and cut into strips. Aqueous medium containing analyte absorbed from the bottom end of the immunostrip dissolved the labeled antibody, and the antigen-antibody binding complex formed was transported into the next nitrocellulose membrane by the flow caused by capillary action. The complex subsequently reacted with the immobilized antibody, which generated a signal in proportion to the analyte concentration. The convective mass transfer of the immunoreactant to the binding partner allowed the assay to be performed with no handling of reagents. The reaction, however, was carried out under nonequilibrium conditions, which resulted in decreased sensitivity as compared with assays performed in an equilibrium mode (e.g., ELISA). To minimize such sacrifice, major factors that control system performance were identified and the system was then devised under optimal conditions.

Bioaffinity based immobilization of enzymes

Procedures that utilize the affinities of biomolecules and ligands for the immobilization of enzymes are gaining increasing acceptance in the construction of sensitive enzyme-based analytical devices as well as for other applications. The strong affinity of polyclonal/monoclonal antibodies for specific enzymes and those of lectins for glycoenzymes bearing appropriate oligosaccharides have been generally employed for the purpose. Potential of affinity pairs like cellulose-cellulose binding domain bearing enzymes and immobilized metal ionsurface histidine bearing enzymes has also been recognised. The bioaffinity based immobilization procedures usually yield preparations exhibiting high catalytic activity and improved stability against denaturation. Bioaffinity based immobilizations are usually reversible facilitating the reuse of support matrix, orient the enzymes favourably and offer the possibility of enzyme immobilization directly from partially pure enzyme preparations or even cell lysates. Enzyme lacking innate ability to bind to various affinity supports can be made to bind to them by chemically or genetically linking the enzymes with appropriate polypeptides/domains like the cellulose binding domain, protein A, histidine-rich peptides, single chain antibodies, etc.

Immunogenicity and pharmacokinetic attributes of poly(ethylene glycol)-grafted immunoliposomes

Immunoliposomes composed of hydrogenated soy phosphatidylcholine, cholesterol, methoxypoly(ethylene glycol)-distearoyl phosphatidylethanolamine (mPEG-DSPE), and hydrazide-PEG-DSPE (mole ratio, 57:38:3.3:1.7) linked to periodate-oxidized chimerized mouse IgG (C225, anti-human epidermal growth factor receptor) were prepared by an optimized aggregation-free procedure. The antigen-binding activity of the immunoliposomes was well preserved. When injected intravenously into naive rats, the immunoliposomes (approximately 18 IgG per 100 nm liposome) exhibited long circulation times (MRT = 8.5 h, Cl = 0.2 ml/h). Subsequent injections of the immunoliposomes into the same animals resulted in rapid clearance (MRT < or = 0.7 h, Cl > or = 7 ml/h), which was accompanied by a significant increase in anti-C225 specific titers. Upon repeated injection or coinjection with the parent liposomes free C225 consistently exhibited prolonged circulation without any increase in C225-specific antisera, but was cleared quickly when administered into animals that had been pretreated with the immunoliposomes. Screening of the immunoliposome induced antisera against human polyclonal IgG and C225-derived Fab' fragment revealed that the immune response was specifically triggered by the constant human region of C225. These results demonstrate that the preparations of PEG-grafted immunoliposomes are more immunogenic than the free IgG component, which is of profound importance to the antibody-mediated liposomal drug delivery effort.

The quantitation of coupled bead antibody by enzyme-linked immunosorbent assay

Quantitation of antibody coupled to a derivatized polystyrene bead through a bifunctional cross linker can be accomplished by a competitive enzyme-linked immunosorbent assay (ELISA) method. This sensitive method is less subject to interference than other protein assay methods such as bicinchoninic acid (BCA) or Lowry. The competitive ELISA method consists of incubating the coupled bead with a (20/80) weight ratio of goat anti mouse kappa alkaline phosphatase/goat anti mouse kappa (GAMKAP/GAMK) for 1.5 hours at 37 degrees C, washing, adding p-nitrophenyl phosphate (PNPP) substrate, and reading the absorbance at 405/450 nm. A standard curve is established with radiolabeled antibody beads for microgram quantitation.

Non-instrumental immunoassay based on coloured polyacrolein latex: application to group-specific polysaccharide of Streptococcus pyogenes

Non-instrumental immunoassay methods based on immunofiltration and microtiter particle agglutination (MPA) techniques have been developed using coloured polyacrolein latex. These methods have been applied to the quantification of the group-specific polysaccharide, A-PS, of S.pyogenes (group A Streptococcus) and compared to the standard ELISA tests. The assay with the ability to detect the lowest concentration of antigen was MPA; as little as 0.05 ng A-PS/ml or 10(4) cells/ml could be detected in 1.5 h. In comparison to ELISA test the sensitivity of MPA was 10 times higher and the procedure of the assay was much more simple. The sensitivity of the immunofiltration assay using both enzyme and latex markers was shown to be the same (50 ng A-PS/ml) and the duration of the assay 3-5 min. No cross-reactions of latex conjugates with non A Streptococcus cell lysates have been observed. The developed methods are easy to perform and require neither sophisticated equipment nor specially trained personal.

Inactivation of human cytomegalovirus by sodium periodate oxidation

Human cytomegalovirus (HCMV), oxidized by sodium periodate (NaIO4), is incapable of giving rise to viral progeny in cell culture. At a NaIO4 concentration as low as 5 mM, there is a loss of at least 6 logs of viral infectivity which occurs very rapidly (less than 5 min). Further, the inactivation is a first-order reaction depending on the periodate concentration. Adsorption to the cell surface, penetration into cells, and penetration of the viral DNA into cell nuclei were found to occur identically in mock oxidized and oxidized HCMV. Since the carbohydrate moiety of viral glycoproteins was the target of periodate attack, these observations strongly suggest that the structural integrity of the sugar residues is not a prerequisite for adsorption and penetration. Nevertheless, no evidence for viral DNA or protein synthesis was detected in cells infected with oxidized virus, and even after 3 weeks in culture, no cytopathic effect was observed.

Covalent binding of biological samples to solid supports for scanning probe microscopy in buffer solution

Scanning force microscopy allows imaging of biological molecules in their native state in buffer solution. To this end samples have to be fixed to a flat solid support so that they cannot be displaced by the scanning tip. Here we describe a method to achieve the covalent binding of biological samples to glass surfaces. Coverslips were chemically modified with the photoactivatable cross-linker N-5-azido-2-nitrobenzoyloxysuccinimide. Samples are squeezed between derivatized coverslips and then cross-linked to the glass surface by irradiation with ultraviolet light. Such samples can be imaged repeatedly by the scanning force microscope without loss of image quality, whereas identical but not immobilized samples are pushed away by the stylus.

Serological detection of HBeAg and anti-HBe using automated microparticle enzyme immunoassays

Fully automated microparticle enzyme immunoassays (EIA) were developed for the detection of HBeAg (IMx HBe) and antibodies against HBeAg (IMx anti-HBe), respectively. Specimens from blood donors, diagnostic and hospital patients and individuals with a variety of infectious and immune diseases were tested both in house and at four clinical sites. The overall agreement between IMx HBe and Abbott HBe RIA/EIA was 99.7% (2985 of 2994) and between IMx anti-HBe and anti-HBe RIA/EIA was 95.8% (2330 of 2432). Almost all anti-HBe discordant specimens (94.1%, 96 of 102) were reactive by IMx anti-HBe but negative by anti-HBe RIA/EIA. off anti-HBe discordant specimens were also reactive for anti-HBc. The IMx anti-HBe assay was 2- to 4-fold more sensitive than the current RIA as determined by serial dilution of anti-HBe reactive specimens. The ability of these IMx assays to detect HBeAg and anti-HBe in 199 HBsAg reactive specimens was also evaluated. 43.7% (87 of 199) and 66.3% (132 of 199) specimens were reactive for HBeAg and anti-HBe by IMx, respectively. Only one specimen was negative for both IMx assays compared to 14 (7.0%) non-reactive for both HBe and anti-HBe RIA. There were 24 specimens (12.1%) positive for both HBeAg and anti-HBe by IMx compared to 1 (0.5%) positive by the corresponding RIAs. This increased detectability of anti-HBe in HBsAg carriers using IMx anti-HBe may result from increased sensitivity for 'free' anti-HBe and/or increased ability to detect anti-HBe in immune complex. IMx anti-HBe also detected more reactives among volunteer blood donor specimens reactive for anti-HBc but negative for HBsAg (55.5%, 86 of 155), compared to RIA (38.7%, 60 of 155). IMx anti-HBe may be useful in confirming prior exposure to HBV in blood screened positive by Corzyme.

A sensitive viral capture assay for detection of plasma viremia in HIV-infected individuals

Human immunodeficiency virus was detected in the serum/plasma of individuals infected with human immunodeficiency virus (HIV) after capture of virions on microparticles coated with monoclonal antibodies to external and transmembrane proteins of HIV-1. We analyzed serial samples obtained from 6 individuals who seroconverted, 18 asymptomatic, and 12 AIDS patients. HIV-1 RNA was detected in all (29/29) seropositive samples and in 6 seronegative samples immediately preceding seroconversion. In contrast, HIV antigen was detected in 13/29 (45%) of seropositive samples. HIV-1 RNA was also detected in 3 antigen-negative samples from one individual 8-5 months prior to seroconversion and in one sample from another person 2 days before antigen positivity. The intensity of the polymerase chain reaction (PCR) signal paralleled the concentration of HIV antigen. Conversely, seropositive HIV antigen-negative samples gave a weaker PCR signal. HIV-1 RNA was detected in 10/18 (60%) samples from asymptomatic, HIV antigen-negative, individuals and in 11/12 (92%) specimens obtained from AIDS patients. The viral capture method may provide a sensitive, specific, and semiquantitative means of detecting circulating HIV at all stages of infection.

Detection of total antibody against hepatitis A virus by an automated microparticle enzyme immunoassay

A fully automated microparticle enzyme immunoassay, IMx HAVAB, was developed for the detection of antibody against hepatitis A virus (anti-HAV). In the IMx HAVAB assay which is run on the IMx instrument, 24 tests are completed in less than 45 minutes. IMx HAVAB sensitivity was 18-25 World Health Organization U/l and was more sensitive than the commercial RIA or EIA, HAVAB and HAVAB EIA, respectively. Specimens from blood donors, diagnostic and hospital patients and individuals with a variety of infectious and immune diseases were tested in parallel with IMx HAVAB and RIA or EIA. Overall agreement of 99.9% (2118/2121) was obtained. Prevalence of anti-HAV tested by IMx ranged from 12.3% in volunteer blood donors in St. Louis to 64.3% for hospital patients in New York City. Discordant specimens were reactive by IMx HAVAB but borderline negative by EIA or RIA, due to the better sensitivity of the IMx assay. IMx HAVAB detected both IgM and IgG subclasses of anti-HAV. Serial bleeds from six intravenous drug users with acute HAV infection were tested over 8 months for the presence of anti-HAV. At all time points, patients were strongly reactive for anti-HAV (titers greater than 1/1000). Anti-HAV titers rose during the first 20 weeks after presentation of symptoms and then declined with time.

Quantitation of hepatitis B surface antibody by an automated microparticle enzyme immunoassay

A fully automated microparticle enzyme immunoassay, IMx AUSAB, was developed for the detection and quantitation of antibody against hepatitis B surface antigen (anti-HBs). The IMx AUSAB assay can complete 24 tests in less than 45 minutes. Anti-HBs concentrations in specimens are calculated automatically by comparison of the specimen rate to values determined from a stored standard curve. IMx AUSAB sensitivity is 2-3 mIU/ml, equivalent in sensitivity to AUSAB RIA or EIA. Specimens from blood donors, diagnostic and hospital patients, hepatitis B vaccinees, and individuals with a variety of infectious and autoimmune diseases tested in parallel by IMx AUSAB and AUSAB RIA or IMx AUSAB and EIA gave overall qualitative agreement of 97.8% (1265/1293) and 99.1% (1281/1293), respectively. The prevalence of anti-HBs ranged from 5.9% in volunteer blood donors to 47.0% of specimens from a sexually transmitted disease clinic. Most discordant specimens (18/34) were low level reactive (less than 10 mIU/ml) by AUSAB RIA, but negative by IMx AUSAB and AUSAB EIA. These specimens were also negative for antibodies to hepatitis B core antigen (anti-HBc). Six discordants were low level reactive by IMx but negative by RIA and EIA. Three of these six specimens were also reactive for anti-HBc suggesting that the IMx AUSAB reactivity resulted from the presence of low level anti-HBs. Quantitative agreement between IMx AUSAB and RIA or IMx and EIA for 106 specimens ranging in anti-HBs concentration from 1 to 30,000 mIU/ml gave linear correlation coefficients of 0.91 and 0.96, respectively. The IMx test was useful for monitoring hepatitis B vaccine response and seroconversion levels after hepatitis B infection.

Purification of measles virus by affinity chromatography and by ultracentrifugation: a comparative study

The purification of viruses by ultracentrifugation in regions with limited resources is often hampered by problems of instrument maintenance. Viral antigens must therefore be imported, which results in delays in obtaining epidemiological data. To address this problem, we undertook the development of purification procedures by affinity chromatography using measles virus (strain Y15) and monkey IgG (anti-measles) coupled covalently via their carbohydrate residues to glass spheres as a model system. The measles virus prepared in this way was compared with measles virus purified by ultracentrifugation using three criteria: the degree of purification, yield and the sensitivity in HA and ELISA. The purification of the antigen by ultracentrifugation (AgU) was undertaken using 10(9) infected cells, and by affinity chromatography (AgAc) using 10(7) infected cells. The total concentration of proteins before purification was 5000 mg for AgU and 11.3 mg for AgAc. After purification by AgU 21.5 mg protein was obtained which was assessed by specific hemagglutinating units (HAU/mg protein) and found to be 179 for AgU and 372-744 for AgAc. Based on total HAU, the yield by centrifugation was 2.4%, whereas the affinity chromatography produced essentially 100%. By ELISA, using reference sera to calibrate the antigens, maximum OD was obtained with 0.5 microgram/well of AgAc and with 2 micrograms/well of AgU. From the relatively small amount of starting material, good yields were obtained with increased specific activity economy in coating by ELISA. These results favour the adoption of affinity chromatography for purifying viral antigens.

Differential diagnosis of acute viral hepatitis using rapid, fully automated immunoassays

We report the development of three rapid, fully automated immunoassays allowing the differential diagnosis of acute viral hepatitis. These assays detect HBsAg, IgM antibody to hepatitis B core antigen (IgM anti-HBc) and IgM antibody to hepatitis A virus (IgM anti-HAV) using the IMx instrument system. All IMx assays were run in less than 45 minutes and all steps were fully automated including specimen dilution steps. Specimens from blood donors, diagnostic and hospital patients, and individuals with a variety of infectious and immune diseases were tested for IgM anti-HAV (n = 1473) or for IgM anti-HBc (n = 1606) or for HBsAg (n = 9700) by the IMx and commercially available EIA and RIA. Each IMx assay showed 99.8% agreement with current EIA. Reproducibility in all hepatitis IMx assays was significantly better than that observed with manual or semiautomated assays; within-run and between-run % CV ranged from 2.2 to 4.8 and 3.5 to 10.3 respectively. In 29 acute hepatitis B patients studied, HBsAg and IgM anti-HBc were detected in the first available patient bleed collected from 0 to 4 week from the onset of symptoms. IgM anti-HBc persisted at reactive levels in the IMx assay for 1 to 24 weeks (mean 12.1 +/- 5.3 weeks) after the patient presented with symptoms. In individuals exposed to hepatitis A, IgM anti-HAV was detectable by IMx by 40 days post exposure (average 33.5 days) and IgM had declined to unreactive levels in IMx for all patients by from 3 to 6 months post exposure. These data demonstrate the use of these rapid IMx assays for differentiation of acute hepatitis A and B.

Improvements in detection of antibody to hepatitis B core antigen by treating specimens with reducing agent in an automated microparticle enzyme immunoassay

A fully automated microparticle enzyme immunoassay (EIA), IMx Core, was developed for the detection of antibody against hepatitis B core antigen (anti-HBc). IMx Core sensitivity was less than 0.5 Paul Ehrlich Institut units per ml and was greater than that of the commercial radioimmunoassay (RIA) or EIA, Corab and Corzyme, respectively. Specimens from blood donors and diagnostic and hospital patients, which included individuals with a variety of infectious and immune diseases, were tested in parallel by the IMx Core and EIA. Overall agreement of 99.1% (4,797 of 4,841) was obtained. Prevalence of anti-HBc tested by IMx Core ranged from 1.2% in volunteer blood donors to 9.1% in hospital laboratories. Discordant specimens reactive by IMx Core but negative by Corzyme or Corab resulted from the increased sensitivity of the IMx Core assay, since other hepatitis B markers were usually present. However, most discordant specimens were positive by the EIA or RIA but negative by IMx Core. No other hepatitis B markers could be detected in these discordants, and after addition of reducing agent, these specimens also became negative by EIA or RIA. In clinical trials, 30% (14 of 47) of volunteer blood donors and 8% (9 of 119) of hospital patients testing repeatedly reactive by the EIA had reduction-sensitive (unspecific) anti-HBc reactivity. The reducing agent, dithiothreitol, was added to each specimen automatically in the IMx assay to eliminate these unspecific reactions without significantly affecting anti-HBc reactivity resulting from hepatitis B virus infection as judged by the correlation with other hepatitis B markers.

A novel covalent enzyme-linked immunoassay (CELIA) for simultaneously measuring free and immune complex bound antibodies of defined specificity. I. Application to naturally occurring antipolyamine antibodies in human sera

A simple covalent enzyme-linked immunoassay procedure (CELIA) is described for the routine determination of free and immune complex-bound antibodies in sera. Assays for the latter could not have been performed by adsorption ELISA due to the high ionic strength of the reassociating buffer. For the measurement in human sera of free naturally occurring IgG and IgM antibody directed against the hapten spermine, polycarboxystyrene microtiter plates with covalently coupled spermine were used. For the determination of immune complex-bound antipolyamine IgG and IgM antibody titers, serum was first dissociated at pH 2.3 in tubes and then reassociated at pH 8.1 in the wells of a microtiter plate containing covalently bound spermine. The reactivity of anti-spermine antibodies was increased from 2- to 13-fold after dissociation and reassociation compared to that of non-dissociated area. The apparent reaction constant (Rapp.) of free IgG antibodies to spermine in the sera of 19 bronchopulmonary patients with cancer differed significantly from Rapp. values of IgG antibodies having this specificity in ten other patients with non-malignant disease.

A novel covalent enzyme-linked immunoassay (CELIA) for simultaneously measuring free and immune complex bound antibodies with a defined specificity. II. Application to immune complexes containing viral antigens in human sera

The coupling of viral antigens from parainfluenza virus (PIV-1), cytomegalovirus (CMV) and human immunodeficiency virus (HIV-1) to chemically functionalized polystyrene plates has permitted us to develop a covalent enzyme-linked immunoassay (CELIA) for measuring the titers of free antibody (Ab) and immune complex (IC) bound Ab directed against each of these viruses. The method was first validated for experimentally produced IC (PIV-anti-PIV) and then applied to the analysis of IC in human sera. In the case of a renal transplant patient with CMV viremia whose free Ab titers were less than 100, the method unambiguously permitted the IC bound anti-CMV titers to be determined. In the case of a survey for HIV-1 Ab, it also allowed us to identify a sub-group of seropositives with IC anti-HIV. In view of the ease and rapidity with which CELIA can be performed, this technology should enable determinations of IC bound Ab of defined specificity to be undertaken routinely in seroepidemiological surveys.

Preparation of a latex reagent for the detection of anti-Staphylococcus aureus ribitol teichoic acid antibodies

Purified S. aureus ribitol teichoic acid was covalently bound to carboxylated latex particles. The immunological properties of the polysaccharide antigen were preserved. The reagent obtained was used for the quantification of anti-ribitol teichoic acid antibodies by means of a direct and rapid agglutination test carried out on a slide. There was good correlation between the preliminary results of this test and those obtained with counter-immunoelectrophoresis (CIE). The method is faster and more sensitive than CIE.

Hydrazido-derivatized supports in affinity chromatography

Many chemistries have been developed for the immobilization of ligands onto insoluble matrices for subsequent use in affinity systems. One such chemistry which has received little attention involves the use of hydrazido-derivatized solid supports. Hydrazine derivatives are strong nucleophiles which will react with a number of functional groups including aldehydes which may be generated on the oligosaccharide moieties of glycoconjugates by specific oxidation reactions. This paper presents a brief overview of the chemistries involved and the uses of hydrazido-derivatized solid supports for the site-directed immobilization of glycoconjugates. Specific examples from the literature on the uses of affinity matrices prepared by this method are cited.

Direct method for detecting small quantities of hepatitis B virus DNA in serum and plasma using the polymerase chain reaction

Serum components inhibit DNA polymerase, thereby obviating direct detection of serum viral DNA sequences by the polymerase chain reaction (PCR). This has necessitated extraction of nucleic acid from sera before performing PCR and has resulted in loss of sensitivity. By adsorbing virus to a solid surface (microcentrifuge tubes or antibody coated microparticles) followed by proteinase K digestion, as little as three viruses per 200 microliters serum may be directly detected by PCR without nucleic acid extraction. The sensitivity is dependent on the surface area of the adsorptive surface and is increased by having antibodies on the adsorptive surface. The nucleic acid sequence of the amplified DNA fragments may be directly determined by the dideoxy method. Of 24 plasma samples from HBsAg+ volunteer blood donors, HBV DNA was detected in 7 by dot blot assay, 7 by liquid hybridization, and 9 by PCR. PCR detected DNA in every sample that was positive by another assay. Analysis of serial samples of two patients with acute self-limited hepatitis B found detectable HBsAg and pre-S2 antigenemia before HBV DNA by the PCR method. These results suggest that surface antigenemia may precede viremia during acute hepatitis.

Ultrastructural localization of 'anixiopsin': a lectin of the fungus Anixiopsis stercoraria (Hansen) Hansen

In order to localize the 'anixiopsin', a lectin of the keratinolytic fungus Anixiopsis stercoraria, the authors used a monospecific antiserum prepared by immunization of rabbits with their own erythrocytes coated in vitro with 'anixiopsin'. In light and scanning electron microscopies, lectinic sites were visualized by means of latex microspheres sensitized with anti-rabbit IgG antibodies. In transmission electron microscopy using the IgG fraction of the rabbit anti-anixiopsin immune sera and protein A-gold, 'anixiopsin' seemed mainly present on the outermost cell wall layer of the ascospores, in a pseudomembraneous structure dense to electrons. Implications of these results on physical and biological properties of the lectin are discussed.