Abstract
The circumsporozoite protein (CSP) plays a key role in malaria sporozoite infection of both mosquito salivary glands and the vertebrate host. The conserved Regions I and II have been well studied but little is known about the immunogenic central repeat region and the N-terminal region of the protein. Rodent malaria Plasmodium berghei parasites, in which the endogenous CS gene has been replaced with the avian Plasmodium gallinaceum CS (PgCS) sequence, develop normally in the A. stephensi mosquito midgut but the sporozoites are not infectious. We therefore generated P. berghei transgenic parasites carrying the PgCS gene, in which the repeat region was replaced with the homologous region of P. berghei CS (PbCS). A further line, in which both the N-terminal region and repeat region were replaced with the homologous regions of PbCS, was also generated. Introduction of the PbCS repeat region alone, into the PgCS gene, did not rescue sporozoite species-specific infectivity. However, the introduction of both the PbCS repeat region and the N-terminal region into the PgCS gene completely rescued infectivity, in both the mosquito vector and the mammalian host. Immunofluorescence experiments and western blot analysis revealed correct localization and proteolytic processing of CSP in the chimeric parasites. The results demonstrate, in vivo, that the repeat region of P. berghei CSP, alone, is unable to mediate sporozoite infectivity in either the mosquito or the mammalian host, but suggest an important role for the N-terminal region in sporozoite host cell invasion.
Highlights
The circumsporozoite protein (CSP) is the predominant surface antigen of Plasmodium sporozoites and is highly immunogenic being one of the key targets recognised by the host immune system
Generation of transgenic parasites Transgenic P. berghei parasites were generated that carried chimeric P. gallinaceum - P. berghei CS genes
In the first transgenic parasite line, the endogenous P. berghei CS (PbCS) gene was substituted with the Plasmodium gallinaceum CS (PgCS) gene in which the repeat region was replaced with the homologous region of P. berghei: line PgCS/PbRR (Figure 1A)
Summary
The circumsporozoite protein (CSP) is the predominant surface antigen of Plasmodium sporozoites and is highly immunogenic being one of the key targets recognised by the host immune system. The central repeat region of P. falciparum CSP, which contains an immunodominant B cell epitope, represented the target of the first two vaccine trials [3,4]. The results of a phase III trial of the RTS,S vaccine, based on both the repeat region and T-cell epitopes from the C-terminal region, provided evidence for protection against both clinical and severe malaria in African children [5]. CSP has long been known to be involved in sporozoite infectivity [10,11]. It appears to be important in the binding of the sporozoite to both mosquito salivary glands [12,13,14] and vertebrate host hepatocytes [15,16,17]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
