Submitted to: Clinical and Vaccine Immunology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/8/2010
Publication Date: 6/23/2010
Citation: Charles, R.C., Sheikh, A., Krastins, B., Harris, J., Bhuiyan, S.M., Larocque, R.C., Logvinenko, T., Sarracino, D.A., Kudva, I.T., Eisenstein, J., Podolsky, M.J., Kalsy, A., Ludwig, A., John, M., Calderwood, S.B., Qadri, F., Ryan, E.T. 2010. Characterization of Anti-Salmonella enterica Serotype Typhi Antibody Responses in Bacteremic Bangladeshi Patients by an Immuno-affinity Proteomic-based Technology (IPT). Clinical and Vaccine Immunology. 17:1188-1195. Interpretive Summary: Salmonella enterica serotype Typhi (S. Typhi) causes typhoid fever only in humans. Currently available typhoid vaccines provide limited protection for about 2-5 years, and the diagnostic tests to identify individuals with typhoid fever lack both sensitivity and specificity. Identifying proteins produced by S. Typhi specifically during human infection could lead to improved diagnostic assays and vaccines. Hence, in this study, we have used the Immuno-affinity Proteomic-based Technology (IPT) to capture these S. Typhi proteins with antibodies present in sera of typhoid patients and subsequently identified the proteins by mass spectrometry. This screening tool identifies immunogenic proteins recognized by antibodies from infected humans. Using this technology and the plasma of typhoid patients in Bangladesh, we identified 57 proteins of S. Typhi, including previously identified proteins, and a number of proteins present only in S. Typhi and another related Salmonella, S. Paratyphi A but rarely found in other Salmonella species. We assessed immune responses of S. Typhi infected patients and uninfected individuals to one of these proteins, HlyE, and detected anti-HlyE responses only in acutely infected patients but not in controls. These findings could assist in the development of improved and differentiating diagnostic assays.
Technical Abstract: Salmonella enterica serotype Typhi (S. Typhi) is the cause of typhoid fever and a human-restricted pathogen. Currently available typhoid vaccines provide only 50-75% protection for 2-5 years, and available diagnostic assays to identify individuals with typhoid fever lack both sensitivity and specificity. Identifying immunogenic S. Typhi antigens expressed during human infection could lead to improved diagnostic assays and vaccines. Here we describe a platform Immuno-affinity Proteomic-based Technology (IPT) that involves the use of columns charged with IgG, IgM or IgA antibody fractions recovered from humans bacteremic with S. Typhi to capture S. Typhi proteins subsequently identified by mass spectrometry. This screening tool identifies immunogenic proteins recognized by antibodies from infected hosts. Using this technology and the plasma of patients with S. Typhi bacteremia in Bangladesh, we identified 57 proteins of S. Typhi, including proteins known to be immunogenic (PagC, HlyE, OmpA, and GroEL), and a number of proteins present in the human-restricted serotypes S. Typhi and S. Paratyphi A but rarely found in broader host-range Salmonella spp. (HlyE, CdtB, PltA, and STY1364). We categorized identified proteins into a number of major groupings, including those involved in energy metabolism, protein synthesis, iron homeostasis, biosynthetic and metabolic functions, and those predicted to localize to the outer membrane. We assessed systemic and mucosal anti-HlyE responses in S. Typhi infected patients, and detected anti-HlyE responses at the time of clinical presentation in patients but not in controls. These findings could assist in the development of improved diagnostic assays.