SUMMARYThe isolation of monoclonal antibodies directed against the trypsin-sensitive site on the 140S particle of foot-and-mouth disease virus (FMDV) has enabled the demonstration of at least three distinct epitopes within this site. Reaction with two of these resulted in neutralization of virus infectivity. None of the epitopes appeared to be present on the 12S particles, and one of the neutralizing epitopes was sensitive to even milder configurational changes of the particle.The ability to stimulate neutralizing, i.e. protective, antibody is largely associated with the nucleocapsid (140S particle) of foot-and-mouth disease virus (FMDV). This property is significantly reduced following treatment of the virus with trypsin (Wild & Brown, 1967). The primary immunogenic determinant on the 140S particle appears to be located on the virion polypeptide (VP1) which is the only polypeptide cleaved by trypsin in situ (Wild et al., 1969) and confined to one or two small tracts containing no more than about 20 amino acid residues (Bachrach et al., 1982;Bittle et al., 1982; Strohmaier et al., 1982). However, information on the nature of the antigenic structures formed by these peptides on their own and perhaps in association with other structures is lacking. For example, although VP1 remains intact in the 12S virion subunit, this particle is far less efficient at provoking neutralizing antibody than the 140S particle (Brown & Newman, 1963 ;Cartwright et al., 1982). We have therefore analysed the antigenic structure of the trypsin-sensitive site of FMDV using monoclonal antibodies as a probe.Monoclonal and hybridoma cell lines secreting antibody of the IgG immunoglobulin class to virus strain O1BFS 1860 were isolated from both mouse (using P3-NS1/Ag4-1 myeloma cells and BALB/c mice) and rat (using the Y3 Ag 1.2.3 myeloma line described by Galfre et al., 1979 and Lou F strain rats) fusions. For the preparation of hybridoma cell lines, sucrose-purified 140S antigen either inactivated with acetylethyleneimine or not inactivated was emulsified in Freund's incomplete adjuvant and inoculated intraperitoneally at 28-day intervals. The second or third injection was given without adjuvant, intravenously 3 to 4 days before the spleens were collected. The techniques for the fusion of myeloma cells with spleen cells and the subsequent isolation and cultivation of antibody-secreting cell lines were essentially those described by McMaster & Williams (1979). Both the indirect sandwich enzyme-linked immunosorbent assay (ELISA) (Ouldridge et al., 1982) and neutralization tests (Booth et al., 1978) were used to detect anti-FMDV-secreting cell lines. Briefly, for the indirect sandwich ELISA, rabbit anti-FMDV IgG was absorbed to flexible PVC microtitre plates; this capture antibody was then used to trap purified 140S antigen. Tissue culture supernatants were then reacted with this antigen and the reaction detected with anti-mouse or-rat IgG antibody linked to horseradish peroxidase. For the detection of neutralizing antibody, serial twofold dil...
Serological evaluations of foot-and-mouth disease type SAT 2 viruses isolated in Kenya between 1979 and 1982 were performed using the two-dimensional microneutralization test. Nine field isolates of epizootiological significance were compared with four vaccine viruses. The results obtained identified Tan 5/68 as the most appropriate reference vaccine virus strain since it had the broadest serological spectrum. Potent Tan 5/68 vaccines would be expected to provide adequate protection against the contemporary SAT 2 field viruses. In the case of K183/74, which also was shown to have a broad spectrum with viruses isolated in Kenya, the results show that the 1982 isolate from central Kenya was significantly divergent (r less than 1.00 at P = 0.01) and warranted tactical revaccination for its control. The study highlighted the fact that strain R1215 which had been isolated from the oesophageal-pharyngeal swabs of asymptomatic carrier cattle had a narrow serological spectrum suggesting that such viruses could be unsuitable as vaccine for the national campaign.
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