Impact of Coinfection on Parasite Clearance in Heligmosomoides polygyrus Trickle Infections

Abstract

The intestinal roundworm Heligmosomoides polygyrus causes chronic infection; however, repeat (trickle) infection confers immunity and facilitates worm clearance. This acquired immunity is associated with a strong Th2 response, notably the enhanced production of intestinal granulomas and parasite-specific antibody. In the natural world rather than the laboratory setting, immune environments are more nuanced. We examined the impact of a mixed Th1/Th2 environment on trickle infection-induced immunity. We used co-infection with Toxoplasma gondii, a Th1-inducing parasite, to achieve this. The mixed infections were associated with lower granuloma numbers. Granulomas also had decreased proportions of key immune cells (eosinophils and M2 macrophages) and an absence of antibody. Parasite-specific antibodies were also absent from the draining lymph nodes. These data confirm the importance of intestinal granulomas and parasite-specific antibody, and highlight why it may be more difficult to clear worms in the field than in the laboratory.