Genetic Diversity Analysis of Surface-Related Antigen (SRA) in Plasmodium falciparum Imported From Africa to China

Plasmodium yoelii surface-related antigen (PySRA) modulates the host pro-inflammatory responses via binding to CD68 on macrophage membrane

Malaria, one of the major infectious diseases in the world, is caused by the Plasmodium parasite. Plasmodium antigens could modulate the inflammatory response by binding to macrophage membrane receptors. As an export protein on the infected erythrocyte membrane, Plasmodium surface-related antigen (SRA) participates in the erythrocyte invasion and regulates the immune response of the host. This study found that the F2 segment of P. yoelii SRA activated downstream MAPK and NF-κB signaling pathways by binding to CD68 on the surface of the macrophage membrane and regulating the inflammatory response. The anti-PySRA-F2 antibody can protect mice against P. yoelii, and the pro-inflammatory responses such as IL-1β, TNF-α, and IL-6 after infection with P. yoelii are attenuated. These findings will be helpful for understanding the involvement of the pathogenic mechanism of malaria with the exported protein SRA.

Immunogenicity Analysis of the Recombinant Plasmodium falciparum Surface-Related Antigen in Mice

Plasmodium falciparum, mainly distributed in tropical and subtropical regions of the world, has received widespread attention owing to its severity. As a novel protein, P. falciparum surface-related antigen (PfSRA) has the structural and functional characteristics to be considered as a malaria vaccine candidate; however, limited information is available on its immunogenicity. Here, we expressed three fragments of recombinant PfSRA in an Escherichia coli system and further analyzed its immunogenicity. The results showed that rPfSRA-immunized mice produced specific antibodies with high endpoint titers (1:10,000 to 1:5,120,000) and affinity antibodies (i.e., rPfSRA-F1a (97.70%), rPfSRA-F2a (69.62%), and rPfSRA-F3a (91.87%)). In addition, the sera of immunized mice recognized both the native PfSRA and recombinant PfSRA, the rPfSRA antibodies inhibited the invasion of P. falciparum into the erythrocytes, and they were dose-dependent in vitro. This study confirmed PfSRA could be immunogenic, especially the F1a at the conserved region N-terminal and provided further support for it as a vaccine candidate against P.falciparum.