title: Functional characterization of Plasmodium berghei PSOP25 during ookinete development and as a malaria transmission-blocking vaccine candidate.
abstract: Plasmodium ookinete surface proteins as post-fertilization target antigens are potential malaria transmission-blocking vaccine (TBV) candidates. Putative secreted ookinete protein 25 (PSOP25) is a highly conserved ookinete surface protein, and has been shown to be a promising novel TBV target. Here, we further investigated the TBV activities of the full-length recombinant PSOP25 (rPSOP25) protein in Plasmodium berghei, and characterized the potential functions of PSOP25 during the P. berghei life-cycle.
  
  
  
  We expressed the full-length P. berghei PSOP25 protein in a prokaryotic expression system, and developed polyclonal mouse antisera and a monoclonal antibody (mAb) against the recombinant protein. Indirect immunofluorescence assay (IFA) and Western blot were used to test the specificity of antibodies. The transmission-blocking (TB) activities of antibodies were evaluated by the in vitro ookinete conversion assay and by direct mosquito feeding assay (DFA). Finally, the function of PSOP25 during Plasmodium development was studied by deleting the psop25 gene.
  
  
  
  Both polyclonal mouse antisera and anti-rPSOP25 mAb recognized the PSOP25 proteins in the parasites, and IFA showed the preferential expression of PSOP25 on the surface of zygotes, retorts and mature ookinetes. In vitro, these antibodies significantly inhibited ookinetes formation in an antibody concentration-dependent manner. In DFA, mice immunized with the rPSOP25 and those receiving passive transfer of the anti-rPSOP25 mAb reduced the prevalence of mosquito infection by 31.2 and 26.1%, and oocyst density by 66.3 and 63.3%, respectively. Genetic knockout of the psop25 gene did not have a detectable impact on the asexual growth of P. berghei, but significantly affected the maturation of ookinetes and the formation of midgut oocysts.
  
  
  
  The full-length rPSOP25 could elicit strong antibody response in mice. Polyclonal and monoclonal antibodies against PSOP25 could effectively block the formation of ookinetes in vitro and transmission of the parasites to mosquitoes. Genetic manipulation study indicated that PSOP25 is required for ookinete maturation in P. berghei. These results support further testing of the PSOP25 orthologs in human malaria parasites as promising TBV candidates.
authors.affiliation: Department of Pathogen Biology, College of Basic Medical Sciences, China Medical University, Shenyang, Liaoning, 110001, China.|Laboratory of Surgery, The Affiliated Hospital, Inner Mongolia Medical University, Hohhot, 010050, China.
authors.forename: Wenqi
authors.initials: W
authors.lastname: Zheng
authors.affiliation: Department of Immunology, College of Basic Medical Sciences, China Medical University, Shenyang, Liaoning, 110001, China.
authors.forename: Fei
authors.initials: F
authors.lastname: Liu
authors.affiliation: Department of Immunology, College of Basic Medical Sciences, China Medical University, Shenyang, Liaoning, 110001, China.
authors.forename: Yiwen
authors.initials: Y
authors.lastname: He
authors.affiliation: Department of Immunology, College of Basic Medical Sciences, China Medical University, Shenyang, Liaoning, 110001, China.
authors.forename: Qingyang
authors.initials: Q
authors.lastname: Liu
authors.affiliation: Department of Entomology, The Pennsylvania State University, University Park, PA, 16802, USA.
authors.forename: Gregory B
authors.initials: GB
authors.lastname: Humphreys
authors.affiliation: Cell-free Science and Technology Research Center, Ehime University, Matsuyama, Ehime, 790-8577, Japan.
authors.forename: Takafumi
authors.initials: T
authors.lastname: Tsuboi
authors.affiliation: Dalian Institute of Biotechnology, Dalian, Liaoning, China.
authors.forename: Qi
authors.initials: Q
authors.lastname: Fan
authors.affiliation: Department of Pathogen Biology, College of Basic Medical Sciences, China Medical University, Shenyang, Liaoning, 110001, China.
authors.forename: Enjie
authors.initials: E
authors.lastname: Luo
authors.affiliation: Department of Immunology, College of Basic Medical Sciences, China Medical University, Shenyang, Liaoning, 110001, China. ymcao@mail.cmu.edu.cn.
authors.forename: Yaming
authors.initials: Y
authors.lastname: Cao
authors.affiliation: Department of Entomology, The Pennsylvania State University, University Park, PA, 16802, USA.
authors.forename: Liwang
authors.initials: L
authors.lastname: Cui
mesh_terms: D000818:Animals; D000913:Antibodies, Protozoan / Q000276:immunology; D000953:Antigens, Protozoan / Q000235:genetics / Q000276:immunology*; D004195:Disease Models, Animal; D018562:Disease Transmission, Infectious / Q000517:prevention & control*; D017353:Gene Deletion; D007116:Immunization, Passive; D008288:Malaria / Q000517:prevention & control*; D017780:Malaria Vaccines / Q000276:immunology*; D051379:Mice; D010962:Plasmodium berghei / Q000235:genetics / Q000254:growth & development* / Q000276:immunology*; D015800:Protozoan Proteins / Q000235:genetics / Q000276:immunology* / Q000378:metabolism
chemical_list: D000913:Antibodies, Protozoan; D000953:Antigens, Protozoan; D017780:Malaria Vaccines; D015800:Protozoan Proteins
keywords: Ookinete; PSOP25; Plasmodium berghei; Transmission-blocking vaccine