Comparison of direct and indirect ELISA for detecting antigenically related cucumoviruses

Serological investigation of highly pathogenic avian influenza H5N2 in ostriches (Struthio camelus)

An ostrich farm of 929 birds that tested polymerase chain reaction-positive for highly pathogenic avian influenza H5N2 in a single sample was designated for culling, despite no evidence of sero-conversion as assessed by haemagglutination inhibition (HI) tests. A month later and immediately prior to culling, all birds were bled and tested with an IDEXX avian influenza virus (AIV) nucleoprotein (NP)-specific enzyme-linked immunosorbent assay (ELISA) and a high sero-prevalence was detected. To address the question of whether the NP-specific antibodies detected indicated exposure to H5 or non-H5 subtypes (H6N2 and H1N2 strains were also circulating regionally at the time), we developed two H5-specific ELISAs, both based on a recombinant H5 HA1 antigen. The H5 indirect ELISA used a horseradish peroxidase ostrich IgY conjugate that we produced in chicken eggs. The single-chain variable fragment (scFv) competitive ELISA (H5 scFv cELISA) used a scFv derived from an H5-immune chicken scFv library. By comparing IDEXX AIV ELISA results with those of the two H5-specific ELISAs and HI tests, we determined that up to 89% of the flock had been exposed to H5N2 AIV. We also detected evidence of suspected vaccination, since 17% of sera contained antibodies against the H5 glycoprotein but not the NP protein. Comparative analytical sensitivity indicated that HI tests are likely to miss up to 35% of H5-positive samples, and thus we consider that H5/H7-specific ELISAs should replace HI tests for ostrich testing in future.

Identification and Subgrouping of Cucumber mosaic virus with Mouse Monoclonal Antibodies

ABSTRACT Using a mixture of isolates of Cucumber mosaic virus (CMV) from subgroups I and II as immunogens, 20 mouse hybridoma cell lines secreting monoclonal antibodies were produced. A reliable method for efficient detection and accurate subgrouping of CMV isolates has been developed. Tests with 12 well-characterized strains of CMV and other cucumoviruses demonstrated the presence of epitopes that were virus and subgroup specific. Analyses of 109 accessions of CMV isolates collected from various parts of the world revealed 70% were subgroup I, with 20% identified as subgroup II. Seven isolates (6%) did not react with group-specific antibodies but did react with antibodies that recognized all CMV isolates. Differential reactions among isolates suggested a total of 10 epi-topes were recognized. The antigenic diversity among subgroup II CMVs was greater than for the subgroup I isolates, even though fewer subgroup II isolates were tested.

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.

Nonspecific binding of immunoglobulins to coat proteins of certain plant viruses in immunoblots and indirect ELISA

Nonspecific binding of immunoglobulins to coat protein of cucumber mosaic virus and several other plant viruses was observed in Western immunoblots, and to a much lesser extent in enzyme-linked immunosorbent assays. The binding appears to occur between immunoglobulin molecules and the basic domains of viral coat proteins which bind to RNA during encapsidation. In all cases tested, the nonspecific reactions could be prevented by addition of 5 U/ml of heparin to the incubation buffers.

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.

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%.

Quantitative microcomplement fixation tests using chicken anti-viral antibody extracted from egg yolk

Yolk immunoglobulins obtained from hens immunized with human rotavirus and two plant virus antigens were used in quantitative microcomplement fixation tests. Difficulties inherent in the use of avian complement were overcome by utilizing a mixture of the C1 component of chicken complement and guinea-pig complement devoid of its own C1. The method is suitable for detecting small quantities of viral antigen and antibody and for detecting antigenic activity present on peptide fragments of viral proteins.

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.

Determination of IgG and IgM levels in serum by rocket immunoelectrophoresis using yolk antibodies from immunized chickens

A method of rocket immunoelectrophoresis based on the use of avian antiglobulin antibodies is described which permits the quantitation of IgG and IgM in human serum. The electrophoretic mobility of avian yolk immunoglobulin (IgY) and mammalian IgG is sufficiently different to obviate the need to chemically modify the antibody, for example by carbamylation. Rockets are obtained in agarose within 3-6 h in 2-(N-morpholino) ethane sulfonic acid buffer at pH 5.5 or 6.0. Avian globulins specific for human IgG and IgM were obtained easily and in large quantities from the egg yolk of hyperimmunized laying hens. The technique is also applicable to quantitation of immunoglobulins in various animal sera.