title: Enhanced protection against Rickettsia rickettsii infection in C3H/HeN mice by immunization with a combination of a recombinant adhesin rAdr2 and a protein fragment rOmpB-4 derived from outer membrane protein B.
abstract: BACKGROUND
  Two surface proteins of Rickettsia rickettsii, outer membrane protein B (OmpB) and adhesion 2 (Adr2), have been recognized as protective antigens. Herein, the immunization with both OmpB and Adr2 was performed in mice so as to explore whether their combination could induce an enhanced immunoprotection against R. rickettsii infection.
  
  
  METHODS
  C3H/HeN mice were immunized with recombinant protein rAdr2 or/and rOmp-4, a fragment derived from OmpB, and then mice were challenged with R. rickettsii. After which rickettsial loads in mice were measured by quantitative PCR. The specific antibodies in mouse sera were determined by ELISA and antigen-specific cytokines secretion by mouse T cells were analyzed in vitro.
  
  
  RESULTS
  After challenge with R. rickettsii, the mice immunized with rAdr2 or/and rOmpB-4 had significant lower rickettsial load in livers, spleens, or lungs compared to PBS mock-immunized mice. Particularly, the load in lungs of mice immunized with both rAdr2 and rOmpB-4 was significantly lower than that with either of them. High levels of specific antibodies were detected in sera from mice immunized with rAdr2 or/and rOmpB-4, but the ratios of specific IgG2a to IgG1 induced by their combination were significantly higher than that by either rAdr2 or rOmpB-4. Following stimulation with rAdr2 or/and rOmpB-4, the INF-γ secreted by CD4(+) T cells from infected mice was significantly higher than that by cognate cells from uninfected mice. And the TNF-α secreted by CD4(+) or CD8(+) T cells from infected mice was markedly greater than that by cognate cells from uninfected mice after stimulation by their combination but not either of them.
  
  
  CONCLUSIONS
  The combination of rAdr2 and rOmpB-4 conferred an enhanced protection against R. rickettsii infection in mice, which was mainly dependent on a stronger Th1-oriented immunoresponse with greater INF-γ and TNF-α secretion by antigen-specific T cells and specific IgG2a elicited by the combination.
authors.affiliation: State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, 20 Dong-Da-Jie Street, Fengtai, Beijing 100071, China.
authors.forename: Wenping
authors.initials: W
authors.lastname: Gong
authors.affiliation: State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, 20 Dong-Da-Jie Street, Fengtai, Beijing 100071, China; Department of Clinical Laboratory, The 105th Hospital of PLA, Hefei, Anhui 230031, China.
authors.forename: Pengcheng
authors.initials: P
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, 20 Dong-Da-Jie Street, Fengtai, Beijing 100071, China. Electronic address: xiongxiaolu624@sohu.com.
authors.forename: Xiaolu
authors.initials: X
authors.lastname: Xiong
authors.affiliation: State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, 20 Dong-Da-Jie Street, Fengtai, Beijing 100071, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Jiao
authors.affiliation: State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, 20 Dong-Da-Jie Street, Fengtai, Beijing 100071, China.
authors.forename: Xiaomei
authors.initials: X
authors.lastname: Yang
authors.affiliation: State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, 20 Dong-Da-Jie Street, Fengtai, Beijing 100071, China. Electronic address: wenbohai@yahoo.com.
authors.forename: Bohai
authors.initials: B
authors.lastname: Wen
mesh_terms: D018829:Adhesins, Bacterial / Q000235:genetics / Q000276:immunology*; D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood / Q000276:immunology; D057134:Antibodies, Neutralizing / Q000097:blood / Q000276:immunology; D000942:Antigens, Bacterial / Q000235:genetics / Q000276:immunology; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000276:immunology*; D016207:Cytokines / Q000096:biosynthesis; D004195:Disease Models, Animal; D007114:Immunization; D008099:Liver / Q000276:immunology / Q000473:pathology; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D011993:Recombinant Fusion Proteins / Q000276:immunology*; D012284:Rickettsia rickettsii / Q000235:genetics / Q000276:immunology*; D012290:Rickettsial Vaccines / Q000235:genetics / Q000276:immunology; D012373:Rocky Mountain Spotted Fever / Q000276:immunology / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism
chemical_list: D018829:Adhesins, Bacterial; D000907:Antibodies, Bacterial; D057134:Antibodies, Neutralizing; D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D016207:Cytokines; D011993:Recombinant Fusion Proteins; D012290:Rickettsial Vaccines
keywords: Adhesin; Outer membrane protein B; Rickettsia rickettsii; Rocky Mountain spotted fever