Investigation of the Cellular Immune Response to Recombinant Fragments of Filamentous Hemagglutinin and Pertactin of Bordetella pertussis in BALB/c Mice

Vaccination with whole-cell or acellular (Ac) vaccines has been very effective for the control of pertussis. The immune response to Ac vaccines has been generally associated with a shift toward the Th2 profile. In the present study, overlapping recombinant fragments of filamentous hemagglutinin (FHA) and pertactin (PRN) were produced in Escherichia coli. BALB/c mice were immunized with recombinant FHA and PRN together with the native pertussis toxin and alum or CpG as adjuvant. Immunized mice were subsequently aerosol challenged with Bordetella pertussis. Bacterial growth was assessed in bronchoalveolar lavage samples and the levels of cytokines were quantitated in supernatants of stimulated splenocytes by enzyme-linked immunosorbent assay. Our results demonstrated that both PRN and FHA antigens were able to induce IFN-γ, IL-4, and to some extent IL-17 cytokines in challenged mice. The level of IFN-γ was higher in response to CpG formulated antigens. These findings indicate immunoprotective efficacy of our recombinant FHA and PRN antigens in mice.

Comparative in vitro and in vivo assessment of toxin neutralization by anti-tetanus toxin monoclonal antibodies

Tetanus is caused by the tetanus neurotoxin (TeNT), a 150 kDa single polypeptide molecule which is cleaved into an active two-chain molecule composed of a 50 kDa N-terminal light (L) and a 100 kDa C-terminal heavy (H) chains. Recently, extensive effort has focused on characterization of TeNT binding receptors and toxin neutralization by monoclonal antibodies (mAbs). Toxin binding inhibition and neutralization is routinely assessed either in vitro by the ganglioside GT1b binding inhibition assay or in vivo using an animal model. These two assay systems have never been compared. In the present study, we report characterization of eleven mAbs against different parts of TeNT. The toxin inhibitory and neutralization activity of the mAbs was assessed in vitro and in vivo respectively. Our data demonstrated that seven mAbs bind to fragment C of the heavy chain, two mAbs react with the light chain, one mAb recognizes both chains and one mAb reacts with neither light chain nor fragment C. Six fragment C specific mAbs were able to inhibit TeNT binding to GT1b ganglioside in vitro but three failed to neutralize the toxin in vivo. One in vitro inhibitory mAb (1F3E3) was found to synergize with the in vivo neutralizing mAbs to reduce toxin lethal activity in vivo. Sequencing of the immunoglobulin heavy and light chain variable region genes revealed that the three in vivo neutralizing mAbs were derived from a common origin. Altogether, our data suggests that fragment C specific mAbs contribute to toxin neutralization in both systems, though some of the GT1b binding inhibitory mAbs may not be able to neutralize TeNT in vivo.

Production and characterization of recombinant light chain and carboxyterminal heavy chain fragments of tetanus toxin

BACKGROUND

Light chain (LC) and heavy chain carboxyterminal subdomain (HCC) fragments are the most important parts of tetanus neurotoxin (TeNT) which play key roles in toxicity and binding of TeNT, respectively. In the present study, these two fragments were cloned and expressed in a prokaryotic system and their identity was confirmed using anti-TeNT specific polyclonal and monoclonal antibodies.

METHODS

LC and HCC gene segments were amplified from Clostridium tetani genomic DNA by PCR, cloned into pET28b(+) cloning vector and transformed in Escherichia coli (E. coli) BL21(DE3) expression host. Recombinant proteins were then purified through His-tag using Nickel-based chromatography and characterized by SDS-PAGE, Western blotting and ELISA techniques.

RESULTS

Recombinant light chain and HCC fragments were successfully cloned and expressed in (E. coli) BL21 (DE3). Optimization of the induction protocol resulted in production of high levels of HCC (~35% of total bacterial protein) and to lesser extends of LC (~5%). Reactivity of the His-tag purified proteins with specific polyclonal and monoclonal antibodies confirmed their renatured structure and identity.

CONCLUSION

Our results indicate successful cloning and production of recombinant LC and HCC fragments of TeNT. These two recombinant proteins are potentially useful tools for screening and monitoring of anti-TeNT antibody response and vaccine production.