Immune response genes modulate serologic responses to Vibrio cholerae TcpApilin peptides

Cholera is an enteric disease caused by Vibrio cholerae. Toxin-coregulated pilus (TCP), a type 4 pilus expressed by V cholerae, is a cholera virulence factor that is required for host colonization. The TCP polymer is composed of subunits of TcpA pilin. Antibodies directed against TcpA are protective in animal models of cholera. While natural or recombinant forms of TcpA ar e difficult to purify to homogeneity, it is anticipated that synthesized Tc pA peptides might serve as immunogens in a subunit vaccine. We wanted to as sess the potential for effects of the immune response (Ir) gene that could complicate a peptide-based vaccine. Using a panel of mice congenic at the H -2 locus we tested the immunogenicity of TcpA peptide sequences (peptides 4 to 6) found in the carboxyl termini of both the classical (CI) and El Tor (ET) biotypes of TCP. Cl peptides have been shown to be immunogenic in CD-1 mice. Our data clearly establish that there are effects of the Ir gene ass ociated with both biotypes of TcpA. These effects are dynamic and dependent on the biotype of TcpA and the haplotypes of the host. In addition to the effects of the classic class II Ir gene, class I (D, L) or nonclassical cla ss I (Qa-2) may also affect immune responses to TcpA peptides. To overcome the effects of the class II Ir gene, multiple TcpA peptides similar to pept ides 4, 5, and 6 could be used in a subunit vaccine formulation. Identifica tion of the most protective B-cell epitopes of TcpA within a particular pep tide and conjugation to a universal carrier may be the most effective metho d to eliminate the effects of the class II and class I Ir genes.