The capsid gene of feline calicivirus contains linear B-cell epitopes in both variable and conserved regions

In order to map linear B-cell (LBC) epitopes in the major capsid protein of feline calicivirus (PCV), an expression library containing random, short ( 100- to 200-bp) fragments of the FCV P9 capsid gene was constructed. Analys is of this library showed it to be representative of the region of the caps id gene that encodes the mature capsid protein. The library was screened by using polyclonal antisera from a eat that had been challenged experimental ly with F9 to identify immunoreactive clones containing LBC epitopes. Twent y-six clones that reacted positively to feline antisera in immunoblots were identified. FCV-derived sequence from these clones mapped to a region of t he capsid that spanned 126 amino acids and included variable regions C and E. An overlapping set of biotinylated peptides corresponding to this region was used to further map LBC epitopes by using F9 antisera. Four principal regions of reactivity were identified. Two fell within the hypervariable re gion at the 5' end of region E (amino acids [aa] 445 to 451 [antigenic site {ags} 2] and aa 451 to 457 [ags 3]). However, the other two were in conser ved regions (aa 415 to 421 [ags 1; region D] and aa 475 to 479 [ags 4; cent ral region F]). The reactivity of the peptide set with antisera from 11 oth er cats infected with a range of FCV isolates was also determined. Ten of 1 1 antisera reacted to conserved ags 4, suggesting that this region may be u seful for future recombinant vaccine design.