Related Experiment Videos
DNA immunisation with Onchocerca volvulus chitinase induces partial protection against challenge infection with L3
R A Harrison1, Y Wu, G Egerton
1Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, UK. robharr@liverpool.ac.uk
Abstract:
The parasitic nematode, Onchocerca volvulus is a major cause of blindness and dermal pathology in tropical regions. A vaccine directed to infective larvae would provide a valuable control tool alongside the current methods of chemotherapy and vector control. Previously we have described the identification of a chitinase cDNA that is expressed in a stage specific manner by O. volvulus infective third stage (L3) larvae. To evaluate its host protective potential, the complete open reading frame was cloned into the eukaryotic expression plasmid pJW4303 and used to vaccinate mice by DNA immunisation with the Accell GeneGun. The survival of challenge infective larvae was monitored using implanted micropore chambers. In the first trial, mice immunised 3 times over 4 months with 1 microg O. volvulus chitinase DNA responded with modest antibody responses dominated by IgG2a and exhibited a 36% (p=0.189, NS) reduction in parasite survival compared with challenge controls. In the second trial, an increased dose of DNA (5 microg) and more frequent immunisations (5 times over 6 months) stimulated an IgG1 dominant response and a 53% reduction in parasite survival (p=0.042). Antibodies from the vaccinated mice reacted with the cuticle of post-infective L3 larvae, implying that this may be the site of immune attack following secretion of chitinase.
Insights
Researchers developed a DNA vaccine targeting the parasitic nematode Onchocerca volvulus, a cause of blindness. Vaccination showed a significant reduction in parasite survival, suggesting potential for a new control strategy.
Area of Science:
- Parasitology
- Immunology
- Molecular Biology
Background:
- Onchocerca volvulus causes significant human disease, including blindness and skin conditions.
- Current control relies on chemotherapy and vector control; a vaccine targeting infective larvae is needed.
- A stage-specific chitinase cDNA from O. volvulus infective larvae was previously identified.
Purpose of the Study:
- To evaluate the host protective potential of O. volvulus chitinase as a vaccine candidate.
- To assess the efficacy of DNA immunization with O. volvulus chitinase in a mouse model.
Main Methods:
- Cloning the O. volvulus chitinase open reading frame into a eukaryotic expression plasmid.
- DNA immunization of mice using the Accell GeneGun with varying DNA doses and schedules.
- Monitoring infective larvae survival using implanted micropore chambers.
- Analyzing antibody responses (IgG1, IgG2a) and antibody reactivity to larval cuticle.
Main Results:
- DNA immunization elicited antibody responses, with IgG2a dominant in the first trial and IgG1 in the second.
- A 36% reduction in parasite survival was observed in the first trial (1 microg DNA, 3 immunizations).
- An increased dose (5 microg DNA, 5 immunizations) resulted in a statistically significant 53% reduction in parasite survival (p=0.042).
- Antibodies reacted with the cuticle of post-infective larvae, suggesting a potential target site.
Conclusions:
- O. volvulus chitinase DNA vaccination can induce a protective immune response against infective larvae.
- Optimized vaccination protocols (dose and frequency) enhance parasite reduction.
- The larval cuticle is a likely target for immune attack mediated by chitinase-specific antibodies.