Immunogenicity of a Cholera Toxin B Subunit Porphyromonas gingivalis Fimbrial Antigen Fusion Protein Expressed in E. coli.
Kim TG, Huy NX, Kim MY, Jeong DK, Jang YS, Yang MS, Langridge WH, Lee JY. Mol Biotechnol. 2008 Sep 20. [Epub ahead of print] PMID: 18807220 Abstract:
The gram-negative anaerobic oral bacterium Porphyromonas gingivalis
initiates periodontal disease through fimbrial attachment to saliva-coated oral surfaces. To study the effects of immunomodulation on enhancement of subunit vaccination, the expression in E. coli
and immunogenicity of P. gingivalis
fimbrial protein (FimA) linked to the C-terminus of the cholera toxin B subunit (CTB) were investigated. Complementary DNAs encoding the P. gingivalis
381 fimbrillin protein sequence FimA1 (amino acid residues 1–200) and FimA2 (amino acid residues 201– 337) were cloned into an E. coli
expression vector downstream of a cDNA fragment encoding the immunostimulatory cholera toxin B subunit (CTB). CTB-FimA1 and CTB-FimA2 fusion proteins synthesized in E. coli
BL21 (DE3) cells were purified under denaturing conditions by Ni2+-NTA affinity column chromatography. Renaturation of the CTB-FimA1 and CTB-FimA2 fusion proteins, permitted identification of CTB-FimA pentamers and restored CTB binding activity to GM1-ganglioside to provide a biologically active CTB-FimA fusion protein. Mice orally inoculated with purified CTB-FimA1 or CTB-FimA2 fusion proteins generated measurable FimA1 and FimA2 IgG antibody titers, while no serum fimbrial IgG antibodies were detected when mice were inoculated with FimA1 or FimA2 proteins alone. Immunoblot analysis confirmed that sera from mice immunized with CTB linked to FimA1 or FimA2 contained antibodies specific for P. gingivalis
fimbrial proteins. In addition, mice immunized with FimA2 or CTB-FimA2 generated measurable intestinal IgA titers indicating the presence of fimbrial antibody class switching. Further, mice orally immunized with CTB-FimA1 generated higher IgA antibody titers than mice inoculated with FimA1 alone. The experimental data show that the immunostimulatory molecule CTB enhances B cell mediated immunity against linked P. gingivalis
FimA fusion proteins in comparison to immunization with FimA protein alone. Thus, linkage of CTB to P. gingivalis
fimbrial antigens can increase subunit vaccine immunogenicity to provide enhanced protection against periodontal disease.