Plasmodium vivax: C-terminal diversity in the blood stage SERA genes from Indian field isolates

Abstract

The burden of Plasmodium vivax malaria is huge in India, affecting a large population annually. Recent reports of P. vivax contributing to severe illness and death, makes vaccine research on P. vivax malaria, a high priority. Extent of sequence variation in antigen coding genes is known to be a major hurdle in vaccine initiatives against malaria. Serine repeat antigens of Plasmodium are promising asexual blood stage vaccine candidates against malaria and have been implicated to have a key role in merozoite invasion and egress. Among the P. vivax SERA proteins, SERA4 and SERA5 are the major transcribed members in erythrocytic stages, making them encouraging candidates to be explored for their polymorphism and vaccine potential. Earlier reports suggest that diversity in these PvSERA antigens is localized to the C-terminal region of the proteins. Hence, genetic diversity study of this region seems prudent. Moreover, as there are no reports available from India, the present study aims to investigate the polymorphism in the C-terminal region of two highly transcribed members PvSERA4 and PvSERA5 in Indian field isolates. Our result of PvSERA5 demonstrates extensive genetic diversity, with major deletions, insertions and SNPs and signifies the gene to be under positive selection. On the other hand, high sequence conservation was seen in the PvSERA4 C-terminal region in Indian field isolates which was contrasting to earlier report from Thailand where they have shown diversity. Research data showcased in this study will greatly aid in gaining better understanding of antigenic variations, immune mediated selection mechanisms and the functional significance of these two vivax proteins. This study also makes a striking contribution towards understanding the antigenic repertoire of PvSERA genes in Indian isolates.