ANALYSIS OF FELINE CALICIVIRUS CAPSID PROTEIN GENES - IDENTIFICATION OF VARIABLE ANTIGENIC DETERMINANT REGIONS OF THE PROTEIN

Three isolates of feline calicivirus (FCV) designated NADC, KCD and CF I/68 were compared for biochemical, serological and genetic variation within the capsid protein gene. The M(r) of the capsid protein from pu rified virions was approximately 66 000 for the NADC virus isolate, wh ich differed slightly from the relative mobilities of the purified cap sid proteins of the KCD and CFI/68 isolates. Polyclonal antisera from either cats infected or rabbits hyperimmunized with the CFI/68 isolate cross-reacted with all three isolates by Western blot analysis. Howev er, these polyclonal antisera to CFI/68 varied considerably in their v irus-neutralization titres to the KCD and NADC isolates. Nucleotide se quence data confirmed the genetic variability among these FCV isolates . Comparison of the predicted amino acid sequence of the capsid protei n among isolates revealed two regions of sequence divergence that prob ably contain the antigenically variable determinants. These hypervaria ble regions may vary by as much as 55 % among isolates of FCV. The ami no acid sequence diversity, in the hypervariable regions of the KCD an d NADC isolates correlated well with the virus-neutralization data and suggests that polyvalent vaccines may be more protective than the com monly used monovalent vaccines.