Foot-and-mouth disease virus-neutralizing antibodies induced in mice by anti-idiotypic antibodies.

A neutralizing monoclonal antibody (nmAb) to foot-and-mouth disease virus (FMDV) was used as antibody-1 (AB1) to induce anti-idiotypic antibodies (a-IdAb) in rabbits. The rabbit a-IdAb (AB2) were isolated on protein A-Sepharose, followed by cycles of separation on idiotype and isotype affinity columns. The specificity of the AB2 for the paratope of AB1 was determined by direct binding to AB1 in solid-phase radioimmunoassay (SP-RIA), and by competition RIA (C-RIA) with virus for binding to the AB1. The AB2, termed a-2PD11, was utilized to immunize six groups of female Swiss mice at weekly intervals with either one of three formulations, in doses of 50 micrograms or 5 micrograms, given in single subcutaneous (s.c.) spots. Anti-viral antibody (AB3) was first detected by RIA at the fifth week in the 50 micrograms/dose groups, and maximum levels were reached at the sixth week in the 50 and 5 micrograms/dose groups. The AB3 levels were at least three times higher for mice given 50 micrograms doses. In addition, the AB3 were also shown to neutralize FMDV infectivity in tissue culture and in a suckling mouse protection assay. Overall, mice exhibited variable responses to immunization with AB2. In a subsequent trial, mice received multispot s.c. and footpad injections of 50 micrograms of a-2PD11 coupled to keyhole limpet haemocyanin (KLH) on a weekly basis. In these mice, AB3 was detected earlier than in mice immunized with single s.c. injections. These results support the use of a-IdAb as potential surrogates of critical determinants for FMD vaccines.