Analysis of cell surface antigens of Campylobacter rectus

Abstract

Campylobacter rectus is one of the predominant bacteria in the lesions of human periodontitis. The surface antigens of the bacterium contain several components which may play significant roles in colonization and pathogenesis. A high-molecular-weight protein was selectively isolated from the cell surface of C. rectus by acid extraction and purified by DEAE Sepharose. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis showed that the extracted protein was 150 kDa. The protein was not found in Campylobacter curvus ATCC 35224 or Wolinella succinogenes ATCC 29543. Lipopolysaccharide (LPS) was extracted from various C. rectus strains by the hot phenol-water method. SDS-PAGE patterns revealed that C. rectus LPS was the smooth type in nature. Monoclonal antibodies against C. rectus were generated by the fusion of SP2/0 myeloma cells with splenocytes from BALB/c mice immunized with whole cells of C. rectus ATCC 33238 strain. An Immunoglobulin G1 monoclonal antibody reacted with the high-molecular-weight proteins from 4 of 9 C. rectus strains, indicating that the 150 kDa protein exhibits antigenic heterogeneity. Immunoelectron microscopic study revealed that the monoclonal antibody recognized the S-layer of C. rectus cells. An IgM monoclonal antibody reacted with LPSs from C. rectus strains at molecular weights between approximately 20.0 kDa and 24.0 kDa. The monoclonal antibody did not react with any other LPSs from C. curvus ATCC 35224 or W. succinogenes ATCC 29543. The reactivities of this monoclonal antibody indicate that it recognizes an O-specific side chain epitope of C. rectus LPS. Sera from patients with adult periodontitis showed strong reactivity with the 150 kDa protein antigen and LPS from C. rectus strains. As determined by immunoblotting analysis, sera from periodontally healthy individuals, however, showed little or no reactivity. The levels of serum IgG antibodies of patients with periodontitis to the protein antigen and LPS were statistically significantly higher than those of periodontally healthy individuals, as assessed by an enzyme-linked immunosorbent assay.