A rapid, automated colorimetric assay for measuring antibody binding to cell surface antigens

An automated, colorimetric procedure is described for detecting antibodies specific for cell surface antigens. The procedure entails (a) coating the wells of 96-well microplates with either protein A or anti-immunoglobulin antibodies and (b) preincubating either the microplate or target cells with the test antibody. Target cells which react with the test antibody bind to the wells of the microplate and bound cells are quantitated by staining with the dye Rose Bengal. A microplate spectrophotometer is used to measure absorbance in each well of the plate, providing a rapid, automated measure of antibody titre. The assay is simple to perform, uses readily available reagents and gives comparable sensitivity to rosetting assays. With these features, and the capacity for handling large numbers of trays quickly, this method has obvious advantages in screening for antibody activity in culture supernatants of hybridoma clones.     

Detection of residual donor leucocytes in leucoreduced red blood cell components using a fluorescence microplate assay

In November 1999, universal leucoreduction of blood components was introduced in the UK to minimise the risk of variant Creutzfeldt-Jakob Disease (vCJD) transmission by blood transfusion. The UK specifications for leucodepletion processes state that 99% of leucodepleted components should contain < 5 x 10(6) leucocytes/unit, within 95% confidence limits. However, this leucocyte concentration is below the detection limits of standard haematology analysers. The development of a fluorometric immunoassay to detect the residual donor leucocytes in leucoreduced blood components is described. Monoclonal antibodies to leucocyte-specific cell surface antigens, CD45 and CD15, were adsorbed to the well surface in 96-well microplates. Red blood cell samples containing low numbers of leucocytes were added to the wells and the cells of interest captured by the monoclonal antibodies. Since leucocytes are the only nucleated cells found in significant numbers in blood components they were quantified using PicoGreen, a fluorescent stain specific for dsDNA. In comparison to flow cytometry, the method currently used to detect low numbers of leucocytes, the microplate assay demonstrated excellent sensitivity (1.00) and acceptable specificity (0.81) when standard leucodepleted samples were tested. There was no significant difference between the two methods (p < or = 0.175). In conclusion, the fluorescence microplate assay represents a simple, high throughput alternative to flow cytometry for monitoring leucodepletion compliance in blood banks.     

Measurement of Myelin Basic Protein and of Anti-Basic Protein Antibodies by Elisa Utilizing Biotinylated Antibodies

Imnunoglobulins were conjugated to peroxidase by the biotin-avidin method and used in ELISA systems for measuring myelin basic protein (MBP) and anti-MBP antibodies. To measure concentration of MBP, microplate wells were coated with affnity purified rabbit anti-MBP antibodies and incubated with varying concentrations of MBP. Bound antigen was measured by incubating with biotinylated anti-MBP antibodies and avidin-peroxidase. As little as 0.2 ng/ml of MBP could be measured by this assay. To measure anti-MBP antibodies, microplate wells were coated with human MBP and incubated with varying concentrations of affinity purified rabbit anti-human MBP antibodies. Binding was measured by incubating with either peroxidase-conjugated anti-rabbit antibodies or biotinylated anti-rabbit antibodies and avidin peroxidase. The two methods were equally sensitive. The avidin-biotin method for enzyme conjugation promises to be a useful and versatile tool for ELISA systems.     

Specific detection and identification of herpes B virus by a PCR-microplate hybridization assay

Herpes B virus DNA was specifically amplified by PCR, targeting the regions that did not cross-react with herpes simplex virus (HSV). The amplified products, which were shown to be highly genetic polymorphisms among herpes B virus isolates, were identified by microplate hybridization with probes generated by PCR. The products immobilized in microplate wells were hybridized with the biotin-labeled probes derived from the SMHV strain of herpes B virus. The amplified products derived from the SMHV and E2490 strains of herpes B virus were identified by microplate hybridization. PCR products amplified from the trigeminal ganglia of seropositive cynomolgus macaques were identified as herpes B virus DNA. The utility of the PCR-microplate hybridization assay for genetic detection and identification of the polymorphic region of herpes B virus was determined.     

微量酶联杂交法定量检测HBV基因 竞争PCR扩增产物

目的 建立一种简便、敏感、精确的微反应板酶联杂交技术,以鉴定HBV基因的竞争PCR扩增产物。方法 设计了两种捕获探针,能分别与竞争PCR扩增产物中的野生片段和突变片段杂交。捕获探针通过3′－端修饰的氨基与微量DNA结合板孔表面的NOS基团化学结合而被“竖直”地包被在反应板上;将热变性后的产物加入两种捕获探针反应孔内,产物中带有生物素的野生或突变片段的一条单链与相应的捕获探针杂交;最后用链亲和素－碱性磷酸酶及底物检测杂交信号。结果 该方法检测PCR产物DNA的灵敏度为80ng/ml,大于琼脂糖凝胶电泳染色鉴定法。获得野生片段和突变片段杂交信号值后,可根据公式计算扩增前野生模板的初始量。结论 本方法操作简单、灵敏度高、结果数据化、特异性强,适用于竞争PCR产物分析。     

Novel microneutralization assay for HCMV using automated data collection and analysis

In addition to being sensitive and specific, an assay for the assessment of neutralizing antibody activity from clinical trial samples must be amenable to automation for use in high-volume screening. To that effect, we developed a 96-well microplate assay for the measurement of HCMV-neutralizing activity in human sera using the HCMV-permissive human cell line HEL-299 and the laboratory strain of HCMV AD169. The degree to which neutralizing antibodies diminish HCMV infection of cells in the assay is determined by quantifying the nuclei of infected cells based on expression of the 72 kDa IE1 viral protein. Nuclear IE1 is visualized using a highly sensitive immunoperoxidase staining and the stained nuclei are counted using an automated ELISPOT analyzer. The use of Half Area 96-well microplates, with wells in which the surface area of the well bottom is half the area of a standard 96-well microplate plate, improves signal detection compared with standard microplates and economizes on the usage of indicator cells, virus, and reagents. The staining process was also streamlined by using a microplate washer and data analysis was simplified and accelerated by employing a software program that automatically plots neutralization curves and determines NT(50) values using 4-PL curve fitting. The optimized assay is not only fast and convenient, but also specific, sensitive, precise and reproducible and thus has the characteristics necessary for use in measuring HCMV-neutralizing activity in the sera of vaccine trial subjects such as the recipients of Vical's HCMV pDNA vaccine candidates.     

Enzyme-linked immunosorbent assay for detection of antibody to leucocytozoon cauller yi

An enzyme-linked immunosorbent assay (ELISA) was used to detect antibodies to Leucocytozoon caulleryi in chicken sera. The assay was standardised in terms of antigen coating conditions, optimum antigen concentration, serum and conjugate dilutions. The schizont antigen showed a strong affinity for binding or absorbing to the surface of the polystyrene wells of the microplate. Nonspecific binding of antigen and cross-reactions were not observed with sera from specific-pathogen-free chickens and antisera against various chicken disease agents. The ELISA was more sensitive than the indirect immuno-fluorescent antibody test and the agar gel precipitation test.     

Pitfalls in laboratory testing for autoantibodies

Quantitative autoantibody determination has recently can be widely used to confirm the diagnosis of autoimmune diseases, however, there are several problems with the assay methods. As pitfalls in terms of measurement methods, in this report we describe actual examples of a problem related to the analysis and of a large discrepancy between the data obtained by different methods of measurement. In the first example, the reaction solution in the microplate evaporated during the reaction process in automated analysis using an Eitest CA-RF ELISA kit, causing the values in the outermost wells to be significantly higher than in the inner wells. In the second example, there was a large discrepancy between the values obtained when the anti-dsDNA antibody of a systemic lupus erythematosus(SLE) patient was measured by radioimmunoassay(RIA) and by enzyme-linked immunosorbent assay(ELISA). The reason for the discrepancy in the second example may have been related to the method of the RIA, which used 50% ammonium sulfate in the B/F separation, and the possibility that certain patients have autoantibody that recognizes the ELISA solid-phase antigen more strongly. Accordingly, quantitative assay data for anti-dsDNA antibody, which possesses such diversity, should be evaluated with due consideration of the characteristics of the assay method and by checking them against the clinical data.     

A microELISA Raji cell assay to detect immune complexes

The Raji cell assay to detect immune complexes has been modified to a microtiter ELISA system. Raji cells were fixed to microplate wells, then reacted with serum samples or aggregated human IgG. Horseradish peroxidase-conjugated anti-human IgG was used to detect bound complexes. There was a linear relationship between aggregated IgG added and optical density reading, with less than 2 micrograms/ml of aggregated IgG readily detected. When applied to human serum this technique gave results comparable to those obtained with the standard Raji cell assay. The Raji micro-ELISA is simpler to perform than the standard assay, is equally reliable, and avoids the hazards of radioactivity.     

A dynamic approach to mapping coordinates between microplates and microarrays

The retrieval of useful data from spotted microarray slides requires keeping track of which microplate wells and DNA sample corresponds to each spot on each array slide. Existing approaches are closely coupled with the type of arrayer in use and are computer operating-system-specific. To support the microarray researcher community at large who use different arrayers and computer platforms, increased flexibility, generality, and portability of these approaches are required. In this paper, we describe a general algorithm that correlates the well positions of DNA samples in each microplate to the positions of the spots on each array slide. Based on this algorithm, we have implemented a flexible and platform-independent program named MicroArray Convolutor (MAC) that provides a Web solution allowing the user to: (a) import a text file that identifies the DNA samples and their well locations, (b) select a transformation method that converts data in 96-well plate format into 384-well plate format, and (c) specify the output format of the array lists dependant on the configuration of the array platform as well as the downstream analysis software chosen for the array. MAC and its source code can be accessed via the following Web address: http://ymd.med.yale.edu/kei-cgi/kc_mac_dev8.pl.     

Low noise bipolar photodiode array protein chip based on on-chip bioassay for the detection of <Emphasis Type="Italic">E. coli</Emphasis> O157:H7

A bipolar photodiode array (PDA) protein chip is presented for the detection of E. coli O157:H7. Through unique design of the bipolar PDA microchip, the device was able to detect E. coli O157:H7 directly on the surface of the bipolar PDA. The bipolar PDA microchip maintained low noise level in the entire process of on-chip protein assay and demonstrated high performance of analog signal processing. At every reaction step of the on-chip bioassay, stability of wet photodiode detection elements was confirmed by monitoring the variance of their photosignals with respect to the irradiated red beam. The background signal represented less than 1.8% variance with respect to maximum signal of photodiode detection elements. As a result of using the on-chip bioassay, any complicated optical alignment and components could be removed in the constructed protein chip. This protein chip enables direct optical detection of E. coli O157:H7 eliminating the need of conventional expensive microplate reader that is incompatible with size of sampling platform of protein chip. The independence of the constructed protein chip on conventional microplate reader can contribute greatly to further miniaturization of protein chip and field usable lab-on-a-chip.     

Rapid screening of monoclonal antibodies by spin adherence double immunosorbent test (SADIST)

The spin adherence double immunosorbent test (SADIST) is a simple, rapid immunoassay with sensitivity similar to the enzyme-linked immunosorbent assay (ELISA). A 1-step SADIST has been found suitable for rapid screening of hybridomas for antigen-specific monoclonal antibodies (MAb). In this procedure hybridoma supernatants are added to antigen coated microplates followed by commercially available antiglobulin beads. The microplate is immediately centrifuged. Wells containing antigen-specific MAb produce a mat of beads whilst wells without antigen-specific MAb produce a button of beads. No washing or incubation steps are necessary and results are read within minutes of adding beads to test supernatants. By comparison, ELISA tests require several hours to perform with multiple wash steps and further reagent additions. A 2-step SADIST was also assessed. Supernatants are incubated in the microplate as for an ELISA and a wash step precedes the addition of antiglobulin beads. A panel of 117 hybridoma supernatants was selected to assess the suitability of the SADIST techniques for hybridoma screening. The supernatants were added to antigen-coated microplates and SADIST and ELISA tests performed. The SADIST correctly discriminated most hybridoma supernatants that were clearly positive or negative by ELISA. It was also found possible to perform SADIST followed by ELISA tests on the same microplate well without significantly affecting ELISA values.     

Cellular FITC-linked immunospecific assay (cell-FLISA) for detection of monoclonal antibodies against cell-surface antigens

A cellular fluorescein isothiocyanate (FITC)-linked immunospecific assay (Cell-FLISA) has been established using the recently developed fluorophotometer for microplates. In the Cell-FLISA system, monoclonal antibodies specific for the surface antigens of live cells are detected by measuring the fluorescence intensity of an FITC-labeled second antibody: goat anti-mouse immunoglobulin antibody. It takes only 2 min to count 96 samples in microplate wells using the fluorophotometer for microplates. Moreover, by this system, the analysis is finished within 2 hr. Thus, the Cell-FLISA system has advantages in screening a large number of samples, such as hybridoma cell lines secreting monoclonal antibodies against cell-surface antigens.     

Measurement of anti-influenza neuraminidase antibody using a peroxidase-linked lectin and microtitre plates coated with natural substrates.

Neuraminidase-induced removal of sialic acid from natural substrates (desialylation) unmasks saccharides that are specifically recognized by the lectin peanut agglutinin (PNA). We demonstrate that, when a neuraminidase substrate is coated on to the wells of a microplate, it is possible to quantitate the binding of PNA to the desialylated substrate using a peroxidase-conjugated PNA (Po-PNA). The amount of bound PNA correlated directly with the amount of sialic acid removed from the substrate and therefore with the neuraminidase activity. By reacting with specific epitopes that are located near to the enzyme active site, anti-neuraminidase antibodies are capable of inhibiting the virus-induced desialylation of the substrate. Such antibodies therefore reduce the binding of Po-PNA. The advantage of this assay is that since different natural substrates for neuraminidase (erythrocytes, fetuin or gangliosides) can be used to coat the microplates, the capacity of anti-neuraminidase antibody to inhibit the neuraminidase activity towards different types of sialoglycoconjugates can be evaluated. Anti-hemagglutinin or non-specific anti-neuraminidase antibody have no interfering reactivity.     

A new method to detect directly in culture cell surface membrane immunoglobulins

An ELISA assay is described for the measurement of the smIgG. The method is based on the detection of cell-smIgG directly on the same microplate used for the culture. The cells, preincubated at 37 degrees C for one hour, were cultured in the presence of S-ConA and serum-free medium for two days. Using this strategy, the background noise due to non specific adsorption of IgG to plastic wells and cytophilic antibodies was eliminated. The cells in the presence of S-ConA and serum-free medium adhered to the plastic wells, and the cell-smIgG were detected using an anti-human IgG covalently linked to alkaline phosphatase or its F(ab')2 fragment. The possibility of measuring the modulation of the expression of the cell-smIgG without any additional manipulation is stressed.     

A preliminary investigation of cell growth after irradiation using a modulated x-ray intensity pattern

In this study we have investigated a spatial distribution of cell growth after their irradiation using a modulated x-ray intensity pattern. An A549 human non-small cell lung cancer cell line was grown in a 6-well culture. Two of the wells were the unirradiated control wells, whilst another two wells were irradiated with a modulated x-ray intensity pattern and the third two wells were uniformly irradiated. A number of plates were incubated for various times after irradiation and stained with crystal violet. The spatial distribution of the stained cells within each well was determined by measurement of the crystal violet optical density at multiple positions in the plate using a microplate photospectrometer. The crystal violet optical density for a range of cell densities was measured for the unirradiated well and this correlated with cell viability as determined by the MTT cell viability assay. An exponential dose response curve was measured for A549 cells from the average crystal violet optical density in the uniformly irradiated well up to a dose of 30 Gy. By measuring the crystal violet optical density distribution within a well the spatial distribution of cell growth after irradiation with a modulated x-ray intensity pattern can be plotted. This method can be used for in vitro investigation into the changes in radiation response associated with treatment using intensity modulated radiation therapy (IMRT).     

A rapid ELISA for measurement of antibodies to nucleic acid antigens using UV-treated polystyrene microplates

Pretreatment of polystyrene microplate wells with certain doses of UV light enhances their capacity for binding to single-stranded DNA, double stranded DNA and various synthetic polynucleotides. The use of UV-irradiated plates to immobilize nucleic acid antigens provides a simple, rapid, and specific ELISA for measuring anti-nucleic acid antibodies. The assay is at least as sensitive as the more complex method of precoating plates with poly(L-lysine). It is useful for detection of anti-DNA antibodies in sera of systemic lupus erythematous patients, as well as in culture fluids of murine and human anti-DNA-secreting hybridomas.     

Phenotype MicroArrays for High-Throughput Phenotypic Testing and Assay of Gene Function

The bacterium Escherichia coli is used as a model cellular system to test and validate a new technology called Phenotype MicroArrays (PMs). PM technology is a high-throughput technology for simultaneous testing of a large number of cellular phenotypes. It consists of preconfigured well arrays in which each well tests a different cellular phenotype and an automated instrument that continuously monitors and records the response of the cells in all wells of the arrays. For example, nearly 700 phenotypes of E. coli can be assayed by merely pipetting a cell suspension into seven microplate arrays. PMs can be used to directly assay the effects of genetic changes on cells, especially gene knock-outs. Here, we provide data on phenotypic analysis of six strains and show that we can detect expected phenotypes as well as, in some cases, unexpected phenotypes.     

Evaluation of three commercial assays for detection of Giardia and Cryptosporidium organisms in fecal specimens

There is an increasing demand for diagnostic testing for Giardia intestinalis (G. lamblia) and Cryptosporidium parvum, with a priority being placed on obtaining diagnostic results in an efficient and timely manner. Several commercial companies have developed rapid diagnostic tests that are simple to perform and can be completed in less time than traditional methods for detecting Giardia and Cryptosporidium: We compared one of these rapid tests, the ImmunoCard STAT! (Meridian Bioscience, Inc.) lateral-flow immunoassay, with the MERIFLUOR direct fluorescent-antibody (DFA) test, the ProSpecT EZ microplate assay for Giardia and the ProSpecT microplate assay for Cryptosporidium, and modified Kinyoun's acid-fast stained smears for the detection of Cryptosporidium using 246 specimens. The MERIFLUOR DFA (Meridian Bioscience, Inc.) test detected the largest number of cases (32 Giardia and 37 Cryptosporidium) infections and was used to calculate the sensitivity and specificity of the other tests. For Giardia, the sensitivities of the ImmunoCard STAT! and the ProSpecT Giardia EZ microplate assay (Alexon-Trend, Inc.) were 81 and 91%, respectively. For detection of Cryptosporidium, the sensitivities of the ImmunoCard STAT!, the ProSpecT Cryptosporidium microplate assay (Alexon-Trend, Inc.), and modified Kinyoun's acid-fast stained smears were 68, 70, and 78%, respectively. Test specificities were equal to or greater than 99%. Specimens with very small numbers of organisms were not detected by the ImmunoCard STAT!, the ProSpecT microplate assay or modified Kinyoun's acid-fast stained smears.     

Measurement of antigen-specific mouse IgE by a fluorometric reverse (IgE-capture) ELISA

A reverse, or IgE-capture, enzyme-linked immunosorbent assay (ELISA) for measuring ovalbumin-specific IgE antibody in the serum of immunized mice has been developed. Microplate wells were first coated with a commercial anti-mouse IgE rat monoclonal antibody, and then incubated with two-fold serial dilutions of test sera with 10% normal mouse serum as diluent for the capturing of only IgE class molecules. Biotinylated ovalbumin and then beta-D-galactosidase-conjugated streptavidin were added and, finally, 4-methylumbelliferyl-beta-D-galactoside was used as the enzyme substrate. The fluorescence intensity of the reaction product (4-methylumbelliferone) was determined on a microplate fluorescence reader. The sensitivity of this assay was equal to that of passive cutaneous anaphylaxis (PCA). In contrast to indirect ELISAs this IgE-capture assay is free from competition by non-IgE antibodies. Furthermore, it requires much less antigen than the PCA assay.