Heterogeneity of neutralization-related epitopes within a bluetongue virus serotype

Twenty-four monoclonal antibodies raised against a 1962 Wyoming isolate of blue-tongue virus serotype 17 (BTV 17) were tested against 20 other field isolates of this serotype in a solid-phase radioimmunoassay (RIA), neutralization, and mouse passive protection tests. Of the 21 antibodies that bound in RIA to acetone-fixed BTV-infected cells, 18 bound to cells infected with any of the BTV 17 isolates and 3 detected minor antigenic differences in two isolates. The remaining 3 antibodies, that bound in RIA only to unfixed virus-infected cells detected additional differences. Of the 3 antibodies binding to unfixed virus-infected cells one bound to all but 2 isolates. A second antibody, 6C3A.2, bound only to the Wyoming isolate and passively protected mice against this isolate. The third antibody, 6C2A.4.2, bound to the Wyoming isolate and to 8 isolates from the mid-South U. S., but not to 12 isolates from California. Antibody 6C2A.4.2 neutralized the Wyoming and mid-South isolates to which it bound and passively protected mice against the Wyoming isolate but provided little or no protection against 4 California isolates tested. Polyclonal serum from mice immunized against Wyoming BTV 17 bound in RIA to all BTV 17 isolates and neutralized all isolates. Thus, three neutralization-related antigenic determinants were disclosed, one (perhaps a set) recognized by immune sera on all BTV 17 isolates, a second recognized by antibody 6C2A.4.2 on the Wyoming and 8 mid-South isolates, and a third recognized by antibody 6C3A.2 only on the Wyoming isolate. These differences may be important in selection of virus strains for vaccine development.