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Idiotypic cross-reactivity between encephalomyocarditis virus (EMCV) neutralizing monoclonal antibodies UM 21.1 (IgG2b) and UM 21.3 (IgG2a) was detected by neutralization inhibition enzyme immunoassay using polyclonal and monoclonal anti-idiotypic antibodies. One strongly cross-reactive anti-idiotypic monoclonal antibody, designated 21.1A5 (IgG2b), might recognize a recurrent idiotope on EMCV neutralizing antibodies but it did not induce EMCV neutralizing anti-anti-idiotypic antibodies in homologous BALB/c mice.

Neutralization inhibition enzyme immunoassay (NI-EIA) was evaluated for its usefulness to detect monoclonal anti-idiotypic antibodies (ab2mAbs) against idiotypic monoclonal antibodies (ab1mAbs) neutralizing either Semliki Forest virus (SFV) or encephalomyocarditis virus (EMCV). Purified ab1mAbs were coupled to keyhole limpet hemocyanin (KLH) mixed with the adjuvant Quil A and then injected intracutaneously into homologous BALB/c mice. Successful fusions were performed 5, 6 and 7 days after intracutaneous booster immunizations of these mice. Ab2mAbs in hybridoma supernatant fluids were detected by their capacity to block virus neutralization by ab1mAbs in NI-EIA. Two stable ab2mAb producing hybridomas were obtained against SFV neutralizing mAb UM 1.13, and twelve against EMCV neutralizing mAb UM 21.1.

Mumps neutralizing monoclonal antibodies (MAs) were purified and labelled with horseradish peroxidase and used to detect virus-infected Vero cells, which were seeded as monolayers in wells of 96-well plates. This direct enzyme immunoassay (EIA) in cell culture proved to be a sensitive method for detection and titration of mumps virus and it may be useful for diagnostic purposes. The EIA is also suitable for the rapid determination of neutralizing antibodies. Neutralization of mumps virus by preincubation with either monoclonal or polyclonal antibodies was indicated by inhibition of the absorbance at 450 nm as measured with a multichannelled photometer. The EIA (duration 2 days) for determination of mumps neutralizing antibodies is an attractive alternative for the plaque reduction test (duration 6 days).