Assessment of immune protective capacity of the recombinant iron-superoxide dismutase (fesod) from bordetella pertussis

Apak, Aycan
Whooping cough (pertussis) is a highly contagious acute respiratory disease caused by the strict human pathogen Bordetella pertussis, a gram-negative coccobacillus. The worldwide mass-vaccination was started in 1940s and to date, a number of whole-cell (Pw) and acellular pertussis vaccine (Pa) formulations were developed. Yet the current vaccines are incapable of providing sustained, lifelong immunity and eliminating subclinical infections, which pose a threat especially for unimmunized infants as well as adolescents and adults. Thus, finding new protein candidates with high immune protective capacities is necessary to enhance the clinical efficacy of current acellular pertussis (Pa) vaccines. In this study, iron-superoxide dismutase (FeSOD) protein was investigated for its capacity of conferring protectivity as well as stimulating humoral and cellular responses against B. pertussis infection in a mouse model. For this purpose, sodB gene, which encodes iron-superoxide dismutase FeSOD protein, was amplified from the genomic DNA of the universal B. pertussis strain ‘Tohama I’ and sequentially cloned to pGEM®-T subcloning and pET-28a(+) expression vectors. Afterwards sodb/pET28a(+) construct was introduced to E. coli BL21(DE3) cells and the gene was overexpressed therein via IPTG induction. The expressed FeSOD protein was then purified by affinity chromatography and its previously reported immunogenicity was confirmed by Western blot. After filter-sterilization, the protein was adsorbed to alum [Al(OH)3] adjuvant and introduced to BALB/c twice at three weeks intervals intraperitoneally at a concentration of 20 μg purified FeSOD protein/mouse. Another group of mice were immunized in tandem with heat-inactivated whole-cell suspension of B. pertussis. Ten days after the second immunization, mice were intranasally challenged with the local ‘Saadet’ strain of B. pertussis. Next the lungs of groups of mice were excised, homogenized and plated as serial dilutions on days 5, 8 and 14 post-challenge, and viable lung CFU counts were carried out. Whole cell immunization conferred complete bacterial clearance following B. pertussis intranasal infection while FeSOD immunization failed to attain such protection. In addition to the protectivity assay, ELISA was performed to assess the humoral (i.e. IgG) immune response triggered upon FeSOD- and whole-cell immunizations and a statistically significant increase in anti-FeSOD IgG production was observed in FeSOD-immunized group. Finally, cellular immune response was tested via cytokine (IFN-γ) assay, in which spleens of mice were excised, splenocytes were cultured and the level of IFN-γ production upon FeSOD addition to the cultures was measured via ELISA. This test showed that whole-cell immunization triggered IFN-γ production at significant levels while FeSOD-immunization did not; indicating the failure of alum-adsorbed FeSOD immunization in inducing cell-mediated immune response.
Citation Formats
A. Apak, “Assessment of immune protective capacity of the recombinant iron-superoxide dismutase (fesod) from bordetella pertussis,” M.S. - Master of Science, Middle East Technical University, 2011.