Priming immune response to cholera toxin induced by synthetic peptides

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Abstract
A systematic study has been conducted of the priming effect in the immunization against cholera toxin (CT). We demonstrate that a priming phenomenon can be achieved by synthetic peptides of the CT B subunit, leading (after a subsequent booster with a subimmunizing dose of the intact toxin) to an efficient anti‐CT neutralizing antibody response. This effect is obtained even upon a single administration of a peptide conjugate and even by peptides that as such are not able to induce CT cross‐reactive antibodies whatsoever. This effect is specific and dose dependent. A macromolecular carrier as well as an adjuvant are essential for the induction of antitoxin response. In this respect, a totally synthetic priming agent, CTP3‐poly (DL‐alanyl)–poly(L‐lysine), was adequate for an effective priming response. The specificity of the antibodies formed after the booster was mainly towards the whole CT molecule and only a small fraction of them were specific towards the peptide used for priming. The ability of synthetic peptides to prime the immune system towards a secondary stimulus with whole organism or native protein might be of general practical value, especially in endemic areas where the population is probably constantly exposed to a low level of a particular infectious agent. This exposure, which has no influence on the unprimed immune system, could serve as a booster in the case of individuals primed with an appropriate peptide, leading to a secondary immune response.