Bowron, J. | Search bioRxiv

bioRxiv2021

Early Th2 cytokine production in Heligmosomoides polygyrus and Toxoplasma gondii co-infected mice is associated with reduced IFNγ production, increased parasite loads and increased mortality

Co-infections are a common reality but understanding how the immune system responds in this context is complex and can be unpredictable. Heligmosomoides bakeri (parasitic roundworm, previously Heligmosomoides polygyrus) and Toxoplasma gondii (protozoan parasite) are well studied organisms that stimulate a characteristic Th2 and Th1 response, respectively. Several studies have demonstrated reduced inflammatory cytokine responses in animals co-infected with such organisms. However, while general cytokine signatures have been examined, the impact of the different cytokine producing lymphocytes on parasite control/clearance is not fully understood. We investigated five different lymphocyte populations (NK, NKT, {gamma}{delta} T, CD4 + T and CD8+ T cells), five organs (small intestine, Peyers patches, mesenteric lymph nodes, spleen and liver), and 4 cytokines (IFN {gamma}, IL-4, IL-10 and IL-13) at two different time points (days 5 and 10 post T. gondii infection). We found that co-infected animals had significantly higher mortality than either single infection. This was accompanied by transient and local changes in parasite loads and cytokine profiles. Despite the early changes in lymphocyte and cytokine profiles, severe intestinal pathology in co-infected mice likely contributed to early mortality due to significant damage by both parasites in the small intestine. Our work demonstrates the importance of taking a broad view during infection research, studying multiple cell types, organs/tissues and time points to link and/or uncouple immunological from pathological findings. Our results provide insights into how co-infection with parasites stimulating different arms of the immune system can lead to drastic changes in infection dynamics.

immunology↗

bioRxiv2020

Host protection to intestinal worm infections: the importance of activated and armed innate effector cells at the host parasite interface.

The intestinal roundworm Heligmosomoides bakeri causes chronic infection in susceptible (C57Bl/6) mice; however, repeat (trickle) infection confers immunity and facilitates worm clearance. We previously showed that this acquired immunity is associated with a strong Th2 response, notably the enhanced production of intestinal granulomas. Here we demonstrate that elevated proportions of IgG1-bound eosinophils and macrophages are observed around the developing tissue worms of trickle-infected female C57Bl/6 mice compared to bolus infected animals. Levels of IgG2c, IgA or IgE were not detected in the granulomas. Increased proportions of SiglecF+ and CD206+ cells, but not Ly6G+ and/or NK1.1+ cells, were also found in the granulomas of trickle-infected mice. However, in the natural world rather than the laboratory setting, immune environments are more nuanced. We examined the impact of a mixed immune environment on trickle infection-induced immunity, using a pre-infection with Toxoplasma gondii. The mixed immune environment resulted in fewer and smaller granulomas with a lack of IgG -bound cells as well as reduced proportions of SiglecF+ and CD206+ cells, measured by immunofluorescence and flow cytometry. This was associated with a higher worm burden in the co-infected animals. Our data confirm the importance of intestinal granulomas and parasite-specific antibody for parasite clearance. They highlight why it may be more difficult to clear worms in the field than in the laboratory. AUTHORS SUMMARYDespite decades of research on intestinal parasitic worms, we are still unable to clearly point to why so many people (approximately 1.8 billion) and most livestock/wild animals are infected with these parasites. We have made progress in understanding how the immune system responds to parasitic worms, and how these parasites manipulate our immune system. However, identifying effective clearance mechanisms is complex and context dependent. We have used models of trickle infection (multiple low doses of parasites) and co-infection (two intestinal parasites) to simulate how people/animals get infected in the real world. Using these models, we have confirmed the host/parasite interface (the granuloma) within the intestinal tissue to be key in determining the hosts ability to clear worms. The lack of specific immune cells and antibodies within the granuloma was associated with chronic infection. Our results help explain why intestinal parasitic worms are so prevalent and why it may be difficult to clear worms in natural settings.

immunology↗