Explaining patterns of infection in free-living populations using laboratory immune experiments.

The host response to different helminth species can vary and have different consequences for helminth persistence. Often these differences are generated by changes in the dynamics and intensity of the immune components against parasites with distinct life history strategies. We examined the immune response of rabbits to primary infections of the gastrointestinal nematodes Trichostrongylus retortaeformis and Graphidium strigosum under controlled conditions for 120 days post-challenge. Results showed that rabbits developed a robust and effective immune response against T. retortaeformis and abundance quickly decreased in the duodenum and was completely cleared in the remaining sections of the small intestine within 4 months. Infected individuals exhibited an initial strong inflammatory response (IFN-γ), IL-4 expression also increased and was coupled to a rapid serum and mucus IgG and IgA and eosinophilia. Strong IL-4, serum IgA and IgG responses and eosinophilia were also observed against G. strigosum. However, parasite abundance remained consistently high throughout the infection, and this was associated with relatively low mucus antibodies. These findings suggest that immunity plays a key role in affecting the abundance of these nematodes, and different immune mechanisms are involved in regulating the dynamics of each infection and their long-term persistence in free-living host populations.