Cross-reactivity between repeat peptides of circumsporozoite proteins (CSPs) of different malaria parasites

Information on the primary sequences of CSP repeat peptides in different malaria parasites is now available. The central third of the CSPs consists of multiple repeating sequences. These repetitive segments are immunodominant epitopes of the CSPs. It has been shown that these repeat units (antigens) cross-react with heterologous peptides (like blood-stage antigens), but so far, no work has been done to show the existence of cross-reactivity between the repeat peptides of different malaria parasites. Using solid phase methodology, we synthesized peptides consisting of repeat units corresponding to four different species of malaria circumsporozoite antigens, namely Plasmodium falciparum (NANP4), P. vivax (DRADGQPAGDRAAGOPAG), P. cynomolgi (AGNNAAGEAGNNAAAGE), P. yeolii (QGPGAP)4. The synthetic peptides were conjugated to bovine serum albumin with glutaraldehyde as the coupling reagent. Four groups of Balb/c mice were immunized with the respective peptide-bovine serum albumin conjugates, and high titer antibodeis were obtained. The antibody raised by a particular species was not found to cross-react wtih the other species of malaria parasites' CSP repeat units