NEUTRALIZING EPITOPES OF FELINE CALICIVIRUS

A new collection of eighteen neutralizing monoclonal antibodies (N-MoAbs), raised against feline calicivirus (FCV), was used to analyze neutralizing epitopes of the F 4 strain of FCV, the prototype strain of FCV in Japan. By cross-neutralization tests with the 20 FCV strains including Japanese, American, Swiss, and New Zealand isolates, the 18 N-MoAbs were categorized into six groups. One N-MoAb (1 D 7) neutralized all the strains tested; eight N-MoAbs neutralized only FCV F 4; while the others neutralized the FCV strains in various degrees. In order to confirm this grouping, eight N-MoAbs were used to select neutralization-resistant variants of FCV F 4. Although no variant against 1 D 7 was obtained, antigenic variants against other N-MoAbs were obtained. Neutralization tests using these variants revealed that there are six neutralizing epitopes on FCV F 4 and that several epitopes are functionally related. One of these epitopes was the same epitope as one of the two epitopes identified by another panel of N-MoAbs we produced previously. Therefore, a total of seven neutralizing epitopes on FCV F 4 were identified. Immunoblot analysis indicated that four of the seven epitopes existed on the 67 kDa capsid protein of the virus.