Mapping and comparison of the B-cell epitopes recognized on thePlasmodium vivaxcircumsporozoite protein by immune Colombians and immunizedAotusmonkeys

Abstract

Plasma samples of individuals from two malaria-endemic villages on the Colombian Pacific coast and synthetic peptides representing different fragments of the central and flanking regions of the Plasmodium vivax circumsporozoite protein (CSP) were used to perform a fine mapping of the B-cell epitopes on the whole CSP. In addition, the immunogenicity of long polypeptides corresponding to the amino (N) and carboxyl (C) regions was evaluated in Aotus monkeys. The epitopes recognized after natural infection of humans and after immunization of Aotus with these synthetic peptides were compared. Human samples more frequently contained specific antibodies to the central region. The type-I repeat region of the CSP was predominantly recognized by the human sera (by 68% of those from the village of Zacarías and 75% of those from Bajo Calima), a significantly smaller population reacting with the type-II repeat (20% and 11%, respectively). Most of the sera reacting with the type-I repeat recognized the minimal epitope AGDR. Although the N- and C-terminal polypeptides were both highly immunogenic in Aotus and induced long-lasting antibodies, titres of antibodies to the C-terminal polypeptide were higher than those of antibodies to the N-terminal. Competitive inhibition assays performed using human and monkey plasma allowed the identification of dominant B-cell epitopes on sequence 71-90 (p8) from the amino region and sequence 332-361 (p24/p25) from the carboxyl region. The high prevalence of naturally induced antibodies to the three epitopes, the possible functional role of the corresponding sequences, and the high immunogenicity of these epitopes in Aotus could be of great importance in the development of a malaria vaccine based on P. vivax CSP.