title: Immune response to Vi polysaccharide, heat-killed whole cells, and outer membrane protein of Salmonella typhi.
abstract: BACKGROUND
  Salmonella typhiVi capsular polysaccharide (ViCPS) is a licensed vaccine against typhoid fever in many countries; in Egypt, the killed whole-cell vaccine is still used. In this study, mice were used as an animal model to evaluate the immune response to ViCPS and other S. typhi antigens such as heat-killed whole cells and outer membrane protein (OMP).
  
  
  METHODS
  The three antigens were laboratory prepared, injected into mice groups, and the humoral response was evaluated using the indirect whole-cell enzyme-linked immunosorbent assay (ELISA). The sensitivity of this assay was investigated using in situ or pre-heated whole cells as coating antigens. In addition, the effect of the immunization route for ViCPS was examined.
  
  
  RESULTS
  Immunizing doses of heat-killed whole cells as well as ViCPS, 2 and 4 µg given subcutaneously (SC) and 4 µg given intraperitoneally (IP), showed significant immune response compared to controls. However, the responses to these doses were not significantly different from each other. The OMP showed a higher significant response. The sensitivity of indirect whole-cell ELISA was enhanced significantly by in situ heat treatment of the coating antigen rather than the pre-heated coating antigen.
  
  
  CONCLUSIONS
  The three antigens showed significant immune response. The immune response to OMP was higher. Though heat-killed whole cells and ViCPS are almost similar in immunizing level, ViCPS is recommended. The SC route was more immunizing than the IP one. Furthermore, the sensitivity of the indirect whole-cell ELISA technique could be enhanced by in situ heat inactivation of the coating cells.
authors.affiliation: Faculty of Pharmacy, Cairo University, Cairo, Egypt. doctor.alaa@hotmail.com.
authors.forename: Alaa El-Din Shawky
authors.initials: Ael-D
authors.lastname: Hosny
authors.forename: Mohamed Reda
authors.initials: MR
authors.lastname: Diab
authors.forename: Rania Abdelmonem
authors.initials: RA
authors.lastname: Khattab
authors.forename: Heba Osama
authors.initials: HO
authors.lastname: Awad
mesh_terms: D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood*; D001425:Bacterial Outer Membrane Proteins / Q000276:immunology*; D004534:Egypt; D004797:Enzyme-Linked Immunosorbent Assay; D051379:Mice; D011135:Polysaccharides, Bacterial / Q000276:immunology*; D012485:Salmonella typhi / Q000276:immunology*; D014436:Typhoid-Paratyphoid Vaccines / Q000008:administration & dosage / Q000276:immunology*; D014611:Vaccination / Q000379:methods*
chemical_list: D000907:Antibodies, Bacterial; D001425:Bacterial Outer Membrane Proteins; D011135:Polysaccharides, Bacterial; D014436:Typhoid-Paratyphoid Vaccines; C054154:capsular polysaccharide, Salmonella