Immune response related to the molecular structure of a peptide from the cholera toxin B subunit

Three forms of a peptide P50-75 from the cholera toxin B subunit in the absence of carrier or adjuvant were administered orally or intraperitoneally to C57Bl/6J mice. Mice were given P50-75 as the free monomer, as an octamer synthesized on the seven polylysine core proposed by Tam (S), or as an octamer synthesized on the epsilon-amino groups of a chain of eight Lys-Gly-Gly units (C). P50-75, presented to the immune system, as monomer or polymers, generated similar serum titres of anti-cholera toxin (CT) antibodies. However, mice immunized orally with the polymers S and C were better protected against the intestinal effects of the toxin than mice immunized with the free monomer P50-75. S and C are more effective than P50-75 or the B subunit in increasing the amounts of total IgA secreted into the intestine and, moreover, the anti-CT IgA neutralized toxin activity. The amounts of anti-CT subclasses (IgG1, IgG2a, IgG2b, and IgG3 plus IgM) produced by the antigens depended on how the peptide P50-75 was presented for priming to the mice boosted thereafter with the B subunit.