Recombinant SpaO and H1a as immunogens for protection of mice from lethal infection with Salmonella paratyphi A: implications for rational design of typhoid fever vaccines.
The Vi capsular polysaccharide vaccine is one of two vaccines against typhoid recommended worldwide and is the vaccine generally used in China. However, in recent years a Salmonella paratyphi A strain that is naturally devoid of capsule has caused frequent outbreaks of typhoid fever in Southern China, leading to the need for identification of additional antigens that could be incorporated into new vaccines. SpaO acts as a major invasion factor of Salmonella enterica spp. and H1a is the unique flagellin subunit ofS. paratyphi A. In this study, the two prokaryotic recombinant antigens, rSpaO and rH1a, were expressed and their immunogenicity was demonstrated by the slide agglutination test and Western blot assays. Using PCR and sequencing analysis as well as ELISA, we find that the spaO and h1a genes are widely distributed in 196 S. paratyphi A isolates (97.5 and 100%, respectively), with high expression frequencies for the SpaO (98.0%) and H1a (100%) antigens. The two genes also show high sequence conservation (similarities from 99.31 to 99.88% for both genes). In sera from 172 paratyphoid A patients, anti-SpaO and anti-H1a IgGs were detectable by ELISA, in 94.8 and 98.8% of patients, respectively. Furthermore, 41.7-66.7% of mice immunized with rSpaO or rH1a alone were protected against subsequent infection, and the protection rate rose to 75.0-91.7% in mice co-immunized with the two antigens. As the spaO and h1a genes of S. paratyphi A are sequence conserved, extensively distributed and highly expressed, the rSpaO and rH1a immunogens should be considered in the development of novel vaccines to prevent S. paratyphi A-caused typhoid fever.
Division of Basic Medical Microbiology, State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, Zhejiang, Hangzhou 310003, PR China.
Ping
P
Ruan
Xiao-Ping
XP
Xia
Dexter
D
Sun
David M
DM
Ojcius
Ya-Fei
YF
Mao
Wen-Yan
WY
Yue
Jie
J
Yan
D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood / Q000276:immunology; D000942:Antigens, Bacterial / Q000235:genetics / Q000276:immunology; D001426:Bacterial Proteins / Q000235:genetics / Q000276:immunology*; D004269:DNA, Bacterial / Q000235:genetics; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000276:immunology*; D051379:Mice; D008807:Mice, Inbred BALB C; D010284:Paratyphoid Fever / Q000276:immunology / Q000517:prevention & control*; D011994:Recombinant Proteins / Q000235:genetics / Q000276:immunology; D012482:Salmonella paratyphi A / Q000235:genetics / Q000276:immunology*; D017422:Sequence Analysis, DNA; D014436:Typhoid-Paratyphoid Vaccines / Q000276:immunology*
D000907:Antibodies, Bacterial; D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D008565:Membrane Proteins; D011994:Recombinant Proteins; C101106:SpaO protein, Salmonella sp.; D014436:Typhoid-Paratyphoid Vaccines