title: The C-terminal domain of Salmonella enterica serovar typhimurium OmpA is an immunodominant antigen in mice but appears to be only partially exposed on the bacterial cell surface.
abstract: We examined the way the major outer membrane protein OmpA of Salmonella enterica serovar Typhimurium is recognized by the mouse immune system, by raising a panel of 12 monoclonal antibodies (MAbs) against this protein. Interaction between OmpA and these MAbs is competitively inhibited with several-hundredfold dilutions of mouse polyclonal sera obtained by immunization with live or heat-killed whole cells, suggesting that OmpA is one of the immunodominant antigens of serovar Typhimurium. All of the MAbs were specific for an identical epitope(s) located on the C-terminal domain of OmpA, as indicated by the use of OmpA fragments generated by protease or cyanogen bromide treatment and by competitive inhibition enzyme-linked immunosorbent assay. This epitope was highly conserved within (but not outside) the family Enterobacteriaceae: The strong immunogenicity of this epitope was surprising because the C-terminal domain of OmpA, usually thought to be located in the periplasm, is not expected to be exposed on the bacterial cell surface. A MAb, however, reacted in a cytofluorometry assay more strongly with outer-membrane-permeabilized cells than with untreated cells, a result supporting the predominantly periplasmic localization of the epitope. Significant, though low-level, reactivity of intact cells nevertheless suggests that in some cells the C-terminal domain of OmpA is exposed on the surface, a result consistent with the proposal that OmpA can fold into one of the two alternate conformations.
authors.affiliation: Biomedical Research and Training Programs, Alabama State University, Montgomery, Alabama 36101, USA. Singhs@nigms.nih.gov
authors.forename: Shiva P
authors.initials: SP
authors.lastname: Singh
authors.forename: Yvonne U
authors.initials: YU
authors.lastname: Williams
authors.forename: Stephanie
authors.initials: S
authors.lastname: Miller
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nikaido
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000276:immunology*; D002462:Cell Membrane / Q000276:immunology; D000939:Epitopes; D051379:Mice; D008807:Mice, Inbred BALB C; D011487:Protein Conformation; D017510:Protein Folding; D012486:Salmonella typhimurium / Q000276:immunology*
chemical_list: D000911:Antibodies, Monoclonal; D001425:Bacterial Outer Membrane Proteins; D000939:Epitopes; C078167:OMPA outer membrane proteins