IMMUNORADIOMETRIC ASSAY FOR QUANTITATION OF DIROFILARIA-IMMITIS ANTIGEN IN DOGS WITH HEARTWORM INFECTIONS

  • 1 January 1984
    • journal article
    • research article
    • Vol. 45  (10) , 2055-2061
Abstract
An immunoradiometric assay (IRMA) was developed, optimized, and validated for detection of parasite-specific antigen in sera from hosts with filarial infections, using D. immitis in dogs as a model. The precision, reproducibility, and parallelism of the IRMA were examined, using precision profile analysis. The IRMA had acceptable precision and reproducibility [< 15% intra-assay coefficient of variation (CV)] over a working range of 10 to 2000 ng of D. immitis-antigen (AG)/ml. The IRMA parallelism (agreement between dilutions) was acceptable(< 10% interdilutional CV) with laboratory-spiked D. immitis AG sera containing no D. immitis-antibody (AB). However, it was not acceptable (> 20% interdilutional CV) for analysis of sera from naturally infected dogs containing D. immitis AB, probably due to dissociation of immune-complexed AG with increasing serum dilution. Nonparallelism limited the accuracy of binding data interpolation from the standard curve. Specificity of the IRMA was enhanced by preabsorption of the radiolabeled detection antibody with Toxocara canis AG before use. Varying amounts of D. immitis AG (22-1000 ng/ml) were detected in 42% (20/48) of microfilaremic dogs. The presence of AG-specific AB at concentrations as low as 1 .mu.g/ml reduced the ability of the IRMA to detect D. immitis AG. Factors that influence the accuracy and sensitivity of immunoassays for circulating filarial antigens are discussed.

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