Comparative sensitivity of different ELISA procedures for detecting monoclonal antibodies

Characterization of cross-reactive norovirus-specific monoclonal antibodies

Noroviruses (NoVs) commonly cause acute gastroenteritis outbreaks. Broadly reactive diagnostic assays are essential for rapid detection of NoV infections. We previously generated a panel of broadly reactive monoclonal antibodies (MAbs). We characterized MAb reactivities by use of virus-like particles (VLPs) from 16 different NoV genotypes (6 from genogroup I [GI], 9 from GII, and 1 from GIV) coating a microtiter plate (direct enzyme-linked immunosorbent assay [ELISA]) and by Western blotting. MAbs were genotype specific or recognized multiple genotypes within a genogroup and between genogroups. We next applied surface plasmon resonance (SPR) analysis to measure MAb dissociation constants (Kd) as a surrogate for binding affinity; a Kd level of <10 nM was regarded as indicating strong binding. Some MAbs did not interact with the VLPs by SPR analysis. To further assess this lack of MAb-VLP interaction, the MAbs were evaluated for the ability to identify NoV VLPs in a capture ELISA. Those MAbs for which a Kd could not be measured by SPR analysis also failed to capture the NoV VLPs; in contrast, those with a measurable Kd gave a positive signal in the capture ELISA. Thus, some broadly cross-reactive epitopes in the VP1 protruding domain may be partially masked on intact particles. One MAb, NV23, was able to detect genogroup I, II, and IV VLPs from 16 genotypes tested by sandwich ELISA, and it successfully detected NoVs in stool samples positive by real-time reverse transcription-PCR when the threshold cycle (CT) value was <31. Biochemical analyses of MAb reactivity, including SPR analysis, identified NV23 as a broadly reactive ligand for application in norovirus diagnostic assays.

Antibodies and intrabodies against huntingtin: production and screening of monoclonals and single-chain recombinant forms

Antibodies can be extremely useful tools for the field of triplet repeats diseases. These reagents are important for localizing proteins in tissues and they can be used in the isolation and characterization of the components of protein complexes. In the context of huntingtin (Htt), antibodies can distinguish Htt with normal or an expanded polyglutamine (polyQ) repeats, and they can identify distinct conformations of Htt. Htt is the protein that, when mutated to contain an expanded polyQ motif, causes Huntington's disease (HD). Our group has produced monoclonal and recombinant single-chain antibodies (intrabodies) that can be used for these purposes and to perturb the function of Htt in living cells. Studies with anti-Htt intrabodies have led to identification of novel pathogenic epitopes. Moreover, some of the isolated intrabodies can reduce the neurotoxicity of mutant Htt in cell culture and animal models of HD. Thus, the production of antibodies and intrabodies has made a significant contribution to the understanding of HD pathogenesis and has introduced a novel strategy to treat this debilitating neurodegenerative disorder.

Improved serological diagnosis of Poplar mosaic virus with monoclonal antibodies

Poplar mosaic virus (PopMV) is widespread in all countries where poplar is grown, and causes severe economic losses in terms of quantity and quality of wood production. Control is based on indexing, aimed at the production of healthy propagation material. The currently used diagnostic method is double antibody sandwich (DAS) ELISA with polyclonal antibodies, which is relatively simple and inexpensive and more reliable than visual inspection of symptoms in the nurseries. However, this method also has disadvantages, mainly low sensitivity in relation to low concentration and irregular distribution of the virus in the plant. In this study, a new diagnostic method for PopMV based on production and use of a monoclonal antibody (Mab) in a triple antibody sandwich (TAS) ELISA, is presented. The TAS-ELISA with monoclonal antibodies was optimised by testing a range of reagent combinations and concentrations. PopMV was detected by the optimised TAS-ELISA with sensitivity more than 100 times higher than by DAS-ELISA with polyclonal antibodies. Six PopMV isolates from four European countries were detected with the same efficiency, indicating that no limitations to the practical use of the TAS-ELISA arise due to excessive epitope-specificity of the monoclonal antibody employed.

Validation of a quantitative ELISA for comparison of monoclonal antibody affinities for isolates of bluetongue virus

The ability of an ELISA-based system to reliably assess the relative affinities of separate monoclonal antibodies (MAbs) for heterologous isolates of bluetongue virus (BTV) was tested. The demonstration that a BTV serogroup-specific MAb (20E9B7G2) possessed equivalent binding properties with the majority of virus isolates tested, permitted a reliable estimation of the relative amount of individual test viruses present in the assay. Subsequent correction for the relative amounts of test viruses and homologous virus present, then allowed monoclonal antibody affinities for heterologous virus isolates to be quantitatively expressed as a function of their homologous binding level and enabled comparisons of individual MAb affinities between virus isolates to be made.

Pitfalls in the use of ELISA to screen for monoclonal antibodies raised against small peptides

Small peptides are often conjugated to large carrier proteins such as thyroglobulin to increase their immunogenicity. Antibodies are raised against peptide, thyroglobulin and contaminants, such as immunoglobulins or BSA in the thyroglobulin preparation, but anti-contaminant antibodies will not be revealed if immune serum is diluted in buffer containing immunoglobulin-contaminated BSA. This may lead to the development of an inappropriate hybridoma-screening assay which detects more anti-contaminant than anti-peptide antibodies if ELISA plates are coated with a capture antibody or blocked with BSA. Dilution of culture supernatants in buffer containing BSA and Tween 20 minimises the risk of false positive results and makes plate-blocking unnecessary. The high affinity peptide-specific antibodies in immune serum, which are more readily detected than lower affinity monoclonal antibodies, may result in an inadequately sensitive hybridoma-screening ELISA.

Epitopes on Cry j I and Cry j II for the human IgE antibodies cross-reactive between Cupressus sempervirens and Cryptomeria japonica pollen

Forty sea from French patients allergic to Cupressus sempervirens pollen were tested for cross-reactivities against Cry j I, Cry j II (major allergens of Cryptomeria japonica pollen) and other pollen allergens from botanically related plants. Seventy-three per cent of the sera reacted with either Cry j I or Cry j II, or with both of them. These IgE cross-reactions were blocked effectively by mAb 046 (anti-Cry j I) or N26, T27 (anti-Cry j II), and weakly by mAbs 052, 027 and 026 (anti-Cry j I). Furthermore, the IgE antibodies in two sera, #40 and #11, bound to peptide fractions obtained from enzyme-digested Cry j I, and mAb 027 could also bind to the fractions. Analyses of the amino acid sequences of the peptides revealed that reactive peptides contained "NGNATPQLTKNAGVLTCSLSKR" sequence and the third residue N3 was glycosylated, however, when the N3 was not glycosylated, the IgE antibodies did not react, but mAb 027 could. The glycosylation of the N3 might be required for IgE-binding to the peptides. Sugar component on the N3 residue was found to be 0.4 mol galactose, 1.3 mol mannose, 0.8 mol fucose and 2.0 mol N-acetyl-glucosamine. Cross-reactivities against other pollen allergens from botanically related plants were found in most of the sera. However, many of these reactivities were detected by sandwich ELISA but not by an ELISA using allergen-coated plates, indicating that it is important to select an appropriate ELISA procedure in order to detect an allergen or an IgE antibody to an allergen.

Interaction between viruses and monoclonal antibodies studied by surface plasmon resonance

An automated biosensor system designed for measuring molecular interactions in real time and without any labelling of the reactants has been used to study the interaction of two animal viruses (vaccinia virus and poliovirus) and two plant viruses (cowpea mosaic virus and tobacco mosaic virus) with monoclonal antibodies. Using monoclonal antibodies specific for different conformational states of viral protein, it was found that the virus particles retained their conformational integrity when immobilized on the dextran matrix present on the sensor chip. Compared to conventional solid phase immunoassays, in which immobilized proteins are usually partly denatured, the biosensor system presents several advantages for studying virus-antibody interaction.

Ultrasound Treatment for Harvesting an Aminopeptidase from Lactic Acid Bacteria and Quantitation of the Enzyme by Enzyme-Linked Immunosorbent Assays

Ultrasound treatment of Lactococcus lactis subsp. cremoris AM2 was optimized to release a maximum amount of intracellular aminopeptidase without modifying the antigenicity of the enzyme. The cells were sonicated three times for 30 s at 23 W. Antibodies produced against the aminopeptidase purified from L. lactis subsp. cremoris AM2 enabled us to use immunoblotting to detect the enzyme in the lysates of all of the lactococci tested but not in the lysates of Leuconostoc strains, lactobacilli, and Streptococcus salivarus subsp. thermophilus . A sandwich enzyme-linked immunosorbent assay (ELISA) was developed to quantify the purified aminopeptidase; the detection limit was 4 ng/ml. The aminopeptidase in the supernatant obtained after the ultrasound treatment of strain AM2 cells was detected with the ELISA starting with a total protein concentration of 200 ng/ml. The proportion of equivalent purified aminopeptidase in the supernatant of L. lactis subsp. cremoris AM2 was about 2% of the total protein. Similarly, the aminopeptidase was quantified in different lactococci; the percentages varied between 0.16 and 2%, depending on the strain. The aminopeptidase content in a mixture of several lactic bacteria was also determined with the sandwich ELISA.

Rapid serotyping of infectious pancreatic necrosis virus by one-step enzyme-linked immunosorbent assay using monoclonal antibodies

A one-step ELISA has been developed for detection and serotyping of infectious pancreatic necrosis virus (IPNV) in infected cell cultures using monoclonal antibodies (mAb) raised against strains representing the Sp, Ab and VR 299 serotypes of IPNV. This assay uses a serotype-specific mAb as capture and a mAb directed against a common epitope as detector antibody. Avidin-peroxidase was employed for amplification. The assay was performed in 90 min by simultaneous incubation of the samples, the biotin labelled mAb and the avidin-peroxidase, and detected 37 ng/ml of purified virus. Serotyping of 34 isolates from different areas of Europe, Asia and America showed a total concordance with the results obtained by the neutralization assay.

Structurally distinct mammalian calmodulins

Rabbits immunized with dinitrophenylated calmodulin produced monospecific antibody against CaM. Using the purified antibody, enzyme-linked immunosorbent assays (ELISAs) were carried out for calmodulin (CaM). The immunological heterogeneity of human and bovine CaMs from erythrocytes was investigated by means of indirect and inhibition ELISAs. The cross-reactivity between the two CaMs was found to be 50% in the indirect ELISA. An eight times higher concentration of human CaM was necessary to produce 30% inhibition in an inhibition assay. The effect of anti-bovine CaM on the stimulation of the red cell membrane calcium pump by human and bovine CaM has also been studied. We have found that (a) the human and bovine CaMs showed indistinguishable activator activities; (b) the antibody partially inhibited the stimulating effects of CaMs; (c) the inhibition was much less effective in the case of stimulation by human CaM. These results suggest that there is a difference in the reactivity of the anti-bovine CaM antibody with bovine and human CaMs. This difference can be attributed to a slight deviation in the antibody binding structure of the two mammalian CaMs in or near the antigenic site of the CaMs.

Production of avian antibodies to three potyviruses in coturnix quail

Avian antibodies against three potyviruses were produced in a small bird, coturnix quail (Coturnix coturnix japonica Temminck et Schlegel), with 15-60 micrograms of purified virus preparations. Intramuscular injections of immunogen with Freund's incomplete or complete adjuvant into the birds did not result in higher titer of antibody compared to that of control birds given intravenous injections. Quail egg yolk antibody was as useful as hen antibody for indirect-ELISA and allowed virus to be detected in purified preparation (10-50 ng/ml) and in crude extracts (10(-6)-10(-7) dilution). The advantages of using quail to produce avian antibodies are discussed.

Monoclonal antibodies directed against the rev protein of human immunodeficiency virus type 1

The rev (art/trs) protein of human immunodeficiency virus type 1 (HIV-1), a phosphoprotein of 20 K apparent molecular weight, is essential to target the mRNA for virion polypeptides into the cytoplasm. The rev protein was expressed in Escherichia coli as a beta-galactosidase fusion protein with a cleavage site for proteinase factor Xa. The rev-specific fragment was isolated to immunize mice. Five stable hybridoma cell lines were obtained producing monoclonal antibodies that reacted with rev protein in Western blot and ELISA. Using the monoclonal antibodies in indirect immunofluorescence, the rev protein could be localized in the nucleus, mostly in the nucleoli, of Hela cells that were transfected with a eukaryotic rev expression plasmid.

Use of a group-reactive and other monoclonal antibodies in an enzyme immunodot assay for identification and presumptive serotyping of aquatic birnaviruses

A panel of monoclonal antibodies (MAbs) was prepared and used to develop an enzyme immunodot assay for the rapid identification and presumptive serotyping of aquatic birnaviruses. Comparison of the reaction patterns of these MAbs with representative virus isolates indicated that one MAb recognizes a serogroup-reactive epitope and can therefore be used for identification of all serogroup A aquatic birnaviruses, the predominant serotype worldwide. Other MAbs exhibited more restrictive specificities, permitting the presumptive serotyping of viruses of the three recognized serotypes and the identification of some individual strains. This assay, in which MAbs are used, is more efficient in terms of time, cost, and case of performance and provides significant advantages in specificity and standardization compared with currently used tests.

Serotype specificity of monoclonal antibodies to cucumber mosaic virus

Ten monoclonal antibodies (McAbs) against cucumber mosaic virus (CMV) have been raised from fusion experiments performed after immunizing mice with different CMV antigens. Their reactivities with members of the three CMV serotypes, CMV-DTL, CMV-ToRS, and CMV-Co were tested in a double antibody sandwich format of enzyme immunosorbent assay (ELISA). Several of the McAbs were specific for different members of the CMV-DTL and CMV-ToRS groups while two allowed the detection of CMV-Co. By using a mixture of two McAbs, any member of the three major CMV serotypes could be detected in infected plant sap. One of the antibodies made it possible to discriminate between subunits and whole virions of CMV-D when it was used in ELISA simultaneously as coating antibody and as biotin-conjugate. McAbs were shown to be useful for quantifying the amount of CMV present in plant sap.

Limitations of different ELISA procedures for localizing epitopes in viral coat protein subunits

The reactivity of monoclonal antibodies (McAbs) to the coat protein of tobacco mosaic virus (TMVP) with the isolated coat protein, disks, virions and a number of antigenic variants of TMV was tested in eight different ELISA procedures. Although certain McAbs, when used as detecting antibody in the liquid phase, did not react with some of these antigens, they were able to bind to them when used as the capturing antibody on the solid phase. This finding was attributed to the ability of the trapping McAb to induce a complementary conformation in the antigen presented in the liquid phase. In many cases, the reactivity of the McAbs was found to depend on the format of the ELISA. This finding together with the presence of oligomers in viral coat protein preparations made it impossible to map TMVP epitopes on the surface of the viral subunit by means of competitive ELISA.

An enzyme immunoassay for prostate-specific p30 antigen detection in the postcoital vaginal tract

A sandwich enzyme immunoassay test utilising a mouse monoclonal antibody has been adapted for the sensitive detection of the p30 prostatic antigen in semen and in postcoital vaginal swabs. In liquid semen, p30 was still detectable at a 1/1,000,000 dilution, and it could still be detected on vaginal swabs 24 h postcoitus.

[Specific monoclonal antibodies to the Mycoplasma-type pathogenic agent of grapevine flavescence dorée]

Three hybridomas producing monoclonal antibodies specific for the mycoplasma-like organism (MLO), pathogenic agent of grapevine flavescence dorée, were obtained after fusion between spleen cells from a mouse immunized against flavescence dorée MLO and Sp2/O-Ag-14 mouse myeloma cells. These hybridomas were selected in an indirect sandwich ELISA in which antibodies from two different animal species were used (rabbit and mouse). This assay is convenient for anti-MLO monoclonal antibody screening, because of its sensitivity, specificity and good preservation of antigens. The three monoclonal antibodies were examined for reactivity towards the MLO causal agents of 15 plant yellows. None of the three were implicated in a serological relationship between the MLO of these plant yellows and flavescence dorée-MLO. Reactivity of the three monoclonal antibodies was checked towards two other isolates of flavescence dorée. One of the three antibodies detected the wild isolates.

Differentiation of peanut clump virus serotypes by monoclonal antibodies

A panel of monoclonal antibodies (mAb) produced against peanut clump virus (PCV) was used to characterize five serotypes of the virus. Four different formats of enzyme-linked immunosorbent assays (ELISA) were compared to establish the most suitable one for diagnosis of infected plants and for serotype differentiation. Since most mAb retained their activity when used for coating microtitre plates, a dual mAb-type assay was found to be most suitable. The same mAb could be used in ELISA as coating and as biotinylated antibody. Because of the ability of mAb to recognize subtle conformational alterations in the viral antigen, it is important to carefully select the ELISA format used for comparing different viral isolates.

Spurious cross-reactions between plant viruses and monoclonal antibodies can be overcome by saturating ELISA plates with milk proteins

It has been claimed recently [Dietzgen (1986) Arch Virol 91: 163-173] that a series of monoclonal antibodies (Mabs) produced against the nepovirus, arabis mosaic virus (ArMV) cross-reacted with the tobamovirus, tobacco mosaic virus (TMV). In the present report, this alleged cross-reactivity was re-examined by two ELISA procedures using Mabs produced against each of the two viruses. It was found that when highly concentrated preparations of Mabs were used, all antibodies reacted in a nonspecific manner with several plant viruses. However, when defatted milk instead of bovine serum albumin was used both as blocking agent and as diluent for the Mabs, the spurious cross-reactions between unrelated viruses were abolished. The use of milk as blocking agent did not prevent the detection of genuine cross-reactions between related nepoviruses.

Purification of monoclonal antibodies against the low-density lipoprotein receptor by preparative isotachophoresis

A preparative free-flow isotachophoretic method for the purification of monoclonal antibodies from mouse ascites fluid and tissue culture media is described. This high-resolution method allows the direct separation of monoclonal antibodies from antibody-containing tissue culture media or ascites fluid and gives a better separation from the major contaminant protein fractions and a higher recovery of the monoclonal antibodies than anion-exchange chromatography. The purification can run continuously and without any time-consuming regeneration procedures; the monoclonal antibody is obtained under mild conditions in a small electrolyte volume.

Specificity of antibodies raised against triacetylated histone H4

Ten monoclonal antibodies (mAbs) were obtained by immunizing animals with triacetylated histone H4 from cuttle-fish. The fine specificity of these antibodies was studied using various populations of acetylated H4, (H3H4)2 tetramers and histone octamers as well as with acetylated and nonacetylated peptides of H4. None of these mAbs were found to recognize triacetylated H4. Only five of them bound to diacetylated, monoacetylated and nonacetylated H4. One antibody was specific for H4 associated in the form of histone octamers and did not bind to any nonacetylated or acetylated form of H4 monomers. Eight of the antibodies were specific for residues situated in the region 9-23 of H4. None of the mAbs was completely specific for acetylated forms of H4. In contrast, antisera raised in rabbits against triacetylated H4 reacted strongly with tri and diacetylated H4, weakly with monoacetylated H4 and barely or not at all with nonacetylated H4.

An enzyme-linked immunosorbent assay utilizing monoclonal antibodies for the characterization of immunoglobulin classes and subclasses of anti-red cell antibodies

The destruction of transfused red cells results from both humoral and cellular immune mechanisms. Numerous factors are likely to affect this destruction. Among them, the class and subclass of antibody-carrying immunoglobulins are of great importance. Compatibility testing routinely realized in vitro in Blood Group Laboratories is not always very helpful in predicting the in vivo significance of alloantibodies. In this sense, we have investigated an enzyme immunoassay that makes it possible to identify the isotype profile of any auto- or alloantibody. This solid-phase immunoassay utilizes mouse monoclonal antibodies specific for individual human IgG subclasses in a double-sandwich test, in which the sample to be analyzed is an eluate obtained by classical absorption-elution methods.

A method for the quantitative analysis of ELISA data

A method is described for measuring relationships among virus serotypes. An indirect ELISA was used to obtain antibody-response curves for homologous and heterologous combinations of virus and dilutions of antibody. Data from the proportional response region of each curve were converted to logarithmic values and subjected to a form of regression analysis to derive relative titres for the various combinations of virus and antibody. SDI values were then obtained by calculating the mean difference in relative titres between homologous and reciprocal heterologous combinations. Virus models in two different groups were examined using this technique. Relative titres obtained were consistent and reproducible over several experiments indicating that the technique was capable of reliably discriminating among serotypes which differed by as little as 0.2 SDI.

A comparison of ELISA screening methods for the production of monoclonal antibodies against soluble protein antigens

A library of monoclonal antibodies against pig heart citrate synthase has been raised. Twelve solid-phase immunoassay systems, employing different methods of antigen immobilization, have been compared for their ability to detect the various members of this library. It was found that a sandwich immunoassay, in which the citrate synthase antigen was immobilized on the solid support via a polyclonal antibody preparation, was the only system capable of detecting all the monoclonal antibodies tested. It is suggested that such a sandwich assay should be used in preference to direct assays for the initial screening of monoclonal antibodies.

Semi-quantitative assessment of anti-insulin total IgG and IgG sub-classes in insulin-immunized patients using a highly sensitive immunochemical micromethod

An immunochemical micromethod was designed to estimate total IgG and IgG sub-classes of anti-insulin antibodies in immunized diabetic patients. Insulin, immobilized on a solid phase, was allowed to react with serum samples containing anti-insulin antibodies. Bound anti-insulin IgG interacted with mouse monoclonal antibodies specific for total IgG or for each IgG isotype. The fixation of mouse monoclonal antibody was subsequently detected using a horseradish peroxidase-conjugated rabbit anti-mouse IgG in the presence of a chromogenic substrate. The test was standardized by an immunocapture assay utilizing coated rabbit anti-human IgG and known concentrations of purified human myelomatous proteins of each sub-class. Results of anti-insulin IgG and anti-insulin IgG sub-classes assay could therefore be expressed in ng equivalent myelomatous proteins per ml of serum. Analysis of serum samples from 24 insulin-immunized diabetic patients revealed a quasi absence of IgG2 anti-insulin antibodies and an increase of the relative abundance of the other three anti-insulin IgG isotypes. In our series, anti-insulin IgG1 was predominant, followed by IgG3 (in 17/24 patients) or IgG4 (in 7/24). Insulin immunization was deduced to be of polyclonal nature, the isotype pattern of which is not representative of the relative proportion of IgG sub-classes in whole normal serum.

Use of egg-yolk antibody for detection of respiratory syncytial virus in nasal secretions by ELISA

Egg-yolk immunoglobulins extracted from the eggs of hens immunized with respiratory syncytial virus (RSV) have been used as a reagent in double sandwich ELISA for detecting RSV in nasal secretions. The sensitivity of virus detection was the same in indirect ELISA, using rabbit anti chicken globulin conjugate, as when biotinylated yolk globulin and labeled avidin were used for detection. The specificity of ELISA for detecting RSV using yolk antibody was similar to that achieved by indirect immunofluorescence using commercial reagents of mammalian origin. Purified immunoglobulin was easily extracted from egg yolk; the amount of globulin present in a single preparation obtained from a batch of ten eggs was sufficient to carry out 10(6) ELISA tests for RSV detection.

Use of the biotin-avidin system for detecting a broad range of serologically related plant viruses by ELISA

The biotin-avidin detection system was used in direct and indirect ELISA for detecting a broad range of serologically related tobamoviruses. When compared to standard ELISA procedures that use antibodies labelled with alkaline phosphatase, the biotin-avidin system increased the assay sensitivity and allowed a wider range of related viral serotypes to be detected.

Dissection of the human antigammaglobulin idiotype system with monoclonal antibodies

Murine monoclonal antibodies (MoAb) were prepared by immunizing mice with human monoclonal rheumatoid factors from patients with mixed cryoglobulinaemia. Indirect solid phase radioimmunoassay and haemagglutination inhibition were used to screen the MoAb. Reactivity patterns of MoAb were determined using (a) polyclonal and monoclonal IgM proteins, (b) monoclonal IgM proteins from patients with neuropathy, (c) monoclonal and polyclonal IgM antigammaglobulins, and (d) various isolated VkIIIb-positive immunoglobulins. Several patterns were obtained: MoAb reacting with private idiotypic determinants, with VkIIIb-related determinants, and with cross-reactive idiotypes (CRI). Two MoAb of the second type reacted with VkIIIb-positive immunoglobulins and light chains regardless of their antigenic activity. Another MoAb reacted with VkIII light chains only when in association with mu heavy chains. MoAb of the third type defined distinct CRI systems. One of these was restricted to antigammaglobulins and another also involved neuropathy-associated monoclonal IgM proteins. All MoAb clearly reacted with a minor population of normal polyclonal IgM, except for the MoAb detecting private idiotypic determinants. Studies using inhibition of binding by enzyme-linked immunosorbent assay showed that polyclonal IgM antigammaglobulins may carry a CRI determinant detected by one of the MoAb. This CRI system, defined by the MoAb Glo 86.3, was similar to but not identical with the previously described Wa CRI, which is widely prevalent among IgM antigammaglobulins of rheumatoid arthritis.

A method of membrane preparation for immunoassay

Membranes prepared from a variety of solid tissues were used as solid-phase antigens for ELISA or RIA after fixation onto polylysine-primed 96-well plates. The preservation of antigens in these membrane preparations was tested by reactivity in ELISA using 2 monoclonal antibodies: W6/32, which recognizes an HLA framework antigen (a protein antigen) and anti-SSEA-1, directed to a carbohydrate antigen carried on glycoproteins. Levels of antigen deposition and usefulness as solid-phase antigens were assessed for ELISA as compared to RIA. Coated plates may be frozen for many months with preservation of antigenic activity. This method is relatively simple, rapid, and is useful for preparation of tissue antigens for immunoassay, especially for screening monoclonal antibodies.

Use of chicken and rabbit antibodies in a solid phase protein A radioimmunossay for virus detection

A new rapid indirect solid phase radioimmunoassay was developed for the detection of Sindbis virus. Chicken antibodies were adsorbed onto wells in microplates to serve as 'capture antibodies' and rabbit antibodies were used as the second antibody. 125I-labelled protein A that does not bind to chicken antibodies, but binds firmly to rabbit antibodies was used as the tracer. All the steps necessary for the development of the assay are described. The minimal amount of Sindbis virus detectable was around 3 x 10(5) PFU/ml and the interassay reproducibility was about +/- 30%.

Alteration in antibody reactivity with foot-and-mouth disease virus (FMDV) 146S antigen before and after binding to a solid phase or complexing with specific antibody

This paper describes the reactions of a number of monoclonal antibodies produced against purified whole virions of foot-and-mouth disease virus in 3 different enzyme immunoassay systems. The first system used whole virus bound non-covalently to microplates; the second used whole virus trapped by a polyclonal antibody which was bound to microplates; and the third allowed the monoclonal antibodies to react with the whole virions in suspension (liquid phase) before trapping by the solid-phase-bound polyclonal antibody. Different reactions with panels of monoclonal antibodies were observed depending on which system was used. Such variations in reactivity give an insight into the alterations in the expression of virus epitopes in the different enzyme immunoassay systems. The reactions of selected monoclonal antibodies were used to illustrate these changes and the results compared to those obtained in similar systems using polyclonal antisera produced against isolated virion polypeptides.

A liquid-phase ELISA and its use in the identification of epitopes on foot-and-mouth disease virus antigens

An enzyme-linked immunosorbent assay was developed which would detect antigen/antibody reactions in liquid-phase; that is under test conditions which should not alter the structure or reactivity of either antigen or antibody. This liquid-phase ELISA was at least as efficient, both qualitatively and quantitatively, as the double sandwich or antigen-trapping ELISA (Crowther and Abu Elzein, 1979), but six to eight times more sensitive than the indirect ELISA. The liquid-phase test can be used to assay both antisera and hybridoma cultures, and will show the greatest discrimination of antibody specificities. Since the liquid-phase ELISA will detect antibody/antigen reactions which are of direct relevance to the protective immune response in vivo (opsonisation; neutralisation of pathogen infectivity), it is recommended that this assay should be used to characterise the antibody reactivity of antisera and hybridoma culture supernatants.

Use of ELISA for measuring the extent of serological cross-reactivity between plant viruses

The degree of antigenic relatedness between two plant viruses is commonly expressed by a serological differentiation index (SDI) which corresponds to the average number of two-fold dilution steps separating homologous from heterologous precipitin titers. Results obtained with several tobamo- and tombusviruses indicated that the indirect form of the enzyme-linked immunosorbent assay (ELISA) can also be used for calculating SDI values. This was achieved by comparing the antiserum dilutions that lead to the same absorbance measurements (for instance 1.0) when homologous and heterologous viruses are assayed by ELISA. SDI values calculated from ELISA were similar to those obtained from precipitin tests. Because of its greater sensitivity, ELISA is able to quantify weak cross-reactions that are not detectable by precipitin tests.

Immunochemical studies of tobacco mosaic virus--VI. Attempts to localize viral epitopes with monoclonal antibodies

The specificity of 18 monoclonal antibodies directed to tobacco mosaic virus (TMV) was studied by measuring their ability to bind to viral mutants, to other tobamoviruses, to dissociated viral subunits and to peptide fragments of the viral coat protein. The apparent binding specificity of the antibodies was dependent on the type of enzyme-linked immunosorbent assay used, probably because the antigens were disrupted or denatured when attached to the plastic surface of microtiter wells. The capacity of different monoclonal antibodies to detect single substitutions in the viral coat protein was used to delineate some of the topographic epitopes of TMV. By means of computer-generated images of the surface residues of the viral subunit, it was possible to identify certain clusters of residues involved in binding to some of the monoclonal antibodies. The results clearly illustrate the operational limitations encountered when monoclonal antibodies are used for elucidating the antigenic structure of proteins.

An enzyme immunoassay for the screening of monoclonal antibodies to cyclosporin

An enzyme-linked immunosorbent assay (ELISA) has been developed which allows hybridoma cell cultures to be tested for the presence of monoclonal antibodies specific for cyclosporin A. Immunization of mice with free cyclosporin was found to be preferable to immunization with cyclosporin-carrier conjugates. It is hoped that the availability of monoclonal antibodies to cyclosporin will clarify the contribution of cyclosporin metabolites to immunosuppression and nephrotoxicity.