WHO collaborative studies on enterovirus reference antisera; fourth report.

This paper summarizes the results of the fourth part of a comprehensive programme undertaken by the WHO International Reference Centre for Enteroviruses and other laboratories for the testing of enterovirus equine antisera prepared for long-term use as reference antisera. The studies were designed to appraise the specificity of the immune serum of horses inoculated with prototype enteroviruses (coxsackievirus types A2, 4, 8, 10, 11, 14-16, 18-21, and 24, and echoviruses E21, 27, 30, 31, and 33). Tests for neutralizing antibody were performed against the homologous viruses and against available regional homotypic strains. Heterotypic tests were performed against reoviruses 1-3, adenoviruses 1-31, and the entire series of enteroviruses (with the exception of enterovirus 68). The homologous geometric mean titre of the 5 echovirus antisera ranged from 3 000 to 10 000; the titre of 1 coxsackievirus antiserum (A24) was only about 400, but the titres of the others ranged from 1 500 to 14 000. All corresponding preinoculation sera were negative. Heterotypic antibody of significant titre was found in 4 antisera: E31 serum against E5 virus, CA8 serum against CA3 virus, CA13 serum against CA18 virus, and CA15 serum against CA2 virus. Information on other heterotypic antibody titres (where found) is recorded for guidance in the use of the sera. The results of homotypic tests with viruses isolated by the collaborating laboratories, though limited in number, were satisfactory.