Plasmodium falciparum Subtilisin-Like Domain Containing Protein ((PfSDP) PF3D7_1105800), a Cross-Stage Antigen, Elicits Short-Lived Antibody Response Following Natural Infection with Plasmodium falciparum

With the increasing detection of artemisinin resistance to front-line antimalarials in Africa and notwithstanding the planned roll-out of RTS’S and R21 in Africa, the search for new vaccines with high efficacy remains an imperative. Towards this endeavor, we performed in silico screening to identify Plasmodium falciparum gametocyte stage genes that could be targets of protection or diagnosis. Through the analysis, we identified a gene, Pf3D7_1105800, coding for a Plasmodium falciparum subtilisin-like do-main-containing protein (PfSDP). Genetic diversity assessment revealed the Pfsdp gene to be relatively conserved across continents with signs of directional selection. Using RT qPCR and western blots, we observed that Pfsdp is expressed in all parasite developmental stages at the transcript and protein levels. Immunofluorescence assays found PfSDP protein colocalizing with PfMSP-1 and partially with Pfs48/45 at the asexual and sexual stages, respectively. Further, we demonstrated that anti-PfSDP peptide-specific antibodies inhibited erythrocyte invasion by 20-60% in a dose-dependent manner, suggesting that PfSDP protein might play a role in merozoites invasion. We also discovered that PfSDP protein is immunogenic in children from different endemic areas with antibody level increasing from acute infection to day 7 post-treatment, followed by a gradual decay. The limited effect of antibodies on erythrocyte invasion could imply that it might be more involved in other processes in the development of the parasite.