Sera from 20 cases of toxoplasmic lymphadenopathy were examined by an enzyme linked immunosorbent assay toxoplasma IgG avidity (ELISA) at two laboratories. The results obtained were largely in agreement and showed that sera from patients with acute infection had low avidity IgG (30% or less), whereas sera from patients with chronic infection had high avidity IgG (40% or more). It is suggested that this type of assay could have a useful complementary role in antenatal testing for toxoplasmosis.

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SUMMARY An enzyme linked immunosorbent assay (ELISA) based on the antibody class capture method for the detection of specific IgM against Toxoplasma gondii, using the microtitre plate format, was developed. Antigen binding was detected using a monoclonal antibody, CIE3, conjugated to horseradish peroxidase. Prior mixing of the conjugate and antigen improved the stability of these reagents as well as removing an incubation stage from the assay. The incubation time of less than four hours permits a rapid throughput of specimens.Using the assay, a total of 163 sera were examined in a three centre study and good agreement was found. Results were expressed as arbitrary enzyme immunoassay units (EIUs) against a freeze dried standard. Throughout the study the standard serum showed a coefficient of variation less than 10% across the microtitre plate. By measuring IgM titres in patients having toxoplasmic lymphadenopathy with a known date of onset, IgM class antibodies were shown to peak at two months, persisting for about six months. In addition, a case of laboratory acquired toxoplasmosis was monitored. Sera shown to contain rheumatoid factor and antinuclear factor did not give false positive results.This rapid, robust, and simplified assay is used by the Public Health Laboratory Service Toxoplasma Reference Units and will provide a standard with which other assays can be compared.

Enzyme-linked immunosorbent assays for IgM antirubella were carried out on 1,546 sera, using an IgM capture method with a F (ab')2 conjugate (ACCA). Under the conditions described, sera containing IgM antirubella bound up to 15 times as much enzyme activity as negative specimens. Paired serum specimens from 27 patients, serial serum specimens from 6 patients, and single serum specimens from 15 patients who had had recent rubella were examined by the haemagglutination inhibition test (HAI) in the presence and absence of 2-mercaptoethanol following sucrose density gradient centrifugation (SDGC). ACCA confirmed all the results found with HAI following SDGC. Specimens were examined from ten patients with congenital rubella; ACCA confirmed the results found with both immunofluorescence following SDGC and radioimmunoassay. Pre- and post-vaccination specimens from 123 patients who had been vaccinated against rubella were examined. An IgM response could only be demonstrated in the 57 cases when IgG was absent in the first specimen. The specificity of the assay was confirmed by testing 31 serum specimens from rubella immune patients that also contained rheumatoid factor, 163 serum specimens from patients with acute infections other than rubella, and 12 serum specimens from infants with miscellaneous neonatal abnormalities other than congenital rubella. The ACCA proved a simple, sensitive, and specific test for IgM antirubella and the results compared favourably with those obtained by the SDGC technique.

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