Public Health Laboratory Service enzymelinked immunosorbent assayfordetecting Toxoplasma specific IgMantibody

SUMMARY Anenzymelinked immunosorbent assay(ELISA) based on theantibody class capture methodforthedetection ofspecific IgMagainst Toxoplasma gondii, using themicrotitre plate format, wasdeveloped. Antigen binding was detected using amonoclonal antibody, CIE3, conjugated tohorseradish peroxidase. Prior mixing oftheconjugate andantigen improved thestability ofthese reagents aswell asremoving anincubation stage fromtheassay.Theincubation timeofless thanfourhours permits a rapid throughput ofspecimens. Using the assay,atotal of163serawereexamined inathree centre study andgoodagreement was found. Results wereexpressed asarbitrary enzymeimmunoassay units (EIUs) against afreeze dried standard. Throughout thestudy thestandard serumshowed acoefficient ofvariation less than10% acrossthemicrotitre plate. Bymeasuring IgMtitres inpatients having toxoplasmic lymphadenopathy with aknowndateofonset, IgMclass antibodies wereshowntopeakattwomonths, persisting foraboutsixmonths. Inaddition, a caseoflaboratory acquired toxoplasmosis was monitored. Serashowntocontain rheumatoid factor andantinuclear factor didnotgive false positive results. Thisrapid, robust, andsimplified assayisusedbythePublic Health Laboratory Service Toxoplasma Reference Units andwill provide a standard withwhichother assayscanbecompared.