O. volvulus mouse-chamber model

by David Abraham


Acquired protective immunity has been demonstrated to larval Onchocerca volvulus in a mouse-diffusion chamber model system. Male BALB/cByJ mice approximately 6 weeks old are used in this model. Larvae are introduced into the mice in diffusion chambers constructed with 5.0micro~ pore size membranes. These membranes allow cells unimpeded entry into the diffusion chambers, yet prevent the larvae from exiting. Twenty-five cryopreserved O. volvulus larvae, from Liberia, are inoculated into each chamber. The diffusion chambers are implanted subcutaneously in the animals' rear flank. Previous studies using irradiated larvae to immunize mice have demonstrated that the optimal time for observing the development of protective immunity was at two weeks postinfection. At this time there was the greatest discrimination between the larval recoveries from control and immunized mice. Approximately 30% to 50% of implanted larvae are recovered from control mice, whereas 10% to 15% of larvae are recovered from immunized mice. Statistically significant differences were also seen at three and four weeks post infection; at six and eight weeks postinfection there was still a difference between the recoveries seen in control and immune mice but the difference was no longer statistically significant. It was also observed that more than 80% of larvae had developed into fourth stage larvae by day seven post-infection. Recovering the diffusion chambers at two weeks postinfection thus ensure that the immune response will have the opportunity of attacking both third and fourth stage larvae.

Protocols for immunization with recombinant antigens can be quite varied. Variables include route, dosage, timing, and adjuvant. It would be of great benefit if the producer of the antigen would supply any available information relating to these variables including specific antibody production and/or cellular responsiveness. If this information is unavailable, the antigen will be tested using standardized routes and adjuvants which are in the process of being determined.

At the conclusion of an experiment, larvae in the diffusion chambers from control and immunized mice will be assessed for their viability. In addition, material will be collected for the following assays, which will be performed when deemed necessary.

1. Larvae will be fixed and studied to determine their developmental stage.
2. Peripheral blood smears will be prepared for blood cell differentials.
3. Serum will be collected for antibody analyses.
4. Cells found within the diffusion chambers will be counted and identified.
5. Supernatants from the diffusion chambers will be collected for analysis for the presence of the cytokines IL-5 and gamma interferon, or antibody.