Constance A. M. Finney

Toxoplasmosis, a disease caused by apicomplexan Toxoplasma gondii (Tg) , is associated with various neuropsychiatric and behavioral conditions. Toxoplasmosis can cause serious complications for those with weakened immune systems and during pregnancy. Cathelicidins, peptides with antimicrobial and immunomodulatory functions, are critical factors in host defense against microbes, but their role in parasitic infections is less well understood. This study demonstrates the protective function of endogenous cathelicidin against hepatic damage caused by Tg infection in an oral infection model. We challenged wild-type ( Camp ^+/+ ) and cathelicidin-deficient ( Camp ^-/- ) mice with low-virulent Type II strain of Tg (ME-49) cysts. Our findings demonstrate that Camp ^-/- mice exhibited more severe clinical manifestations, higher mortality rates, and more pronounced hepatic damage compared to their Camp ^+/+ counterparts. Histological liver examinations indicated significant necrotic hepatitis in Camp ^-/- mice, correlating with increased local concentrations of pro-inflammatory cytokines and proteomic upregulation of poly(ADP-ribose) polymerase 3 and guanylate-binding proteins. Increased cerebral inflammation and Tg cystogenesis were also observed in Camp ^-/- mice. Systemically, Camp ^-/- mice presented elevated levels of pro-inflammatory mediators, specifically interferon-gamma (Ifn-γ) and tumor necrosis factor-alpha (Tnf-α). In cultured macrophages, endogenous cathelicidin increased after Tg challenge, while Camp ^-/- bone marrow-derived macrophages released higher amounts of Tnf-α than their counterparts. We conclude that cathelicidin protects against liver injury and systemic deterioration induced by Tg infection by downregulating the synthesis of pro-inflammatory cytokines.

Introduction: The intestinal roundworm Heligmosomoides bakeri establishes chronic infections in susceptible C57Bl/6 mice, yet repeated (‘trickle’) infections confer immunity and promote worm clearance. We previously linked this acquired immunity to enhanced intestinal granuloma formation. Here, we focused on effector molecules (antibodies) and cells (eosinophils and macrophages) known to immobilize and damage developing parasites. Methods and Results: We used flow cytometry and immunofluorescence to show that granulomas in trickle-infected female mice contain elevated levels of IgG1, SiglecF+ eosinophils and CD206+ macrophages compared to bolus-infected animals, while IgG2c, IgA, and IgE were undetectable and levels of Ly6G+ neutrophils or NK1.1+ NK cells were unchanged. To mimic natural complexity, we introduced a mixed immune environment via prior Toxoplasma gondii infection which induces interferon-γ production in the small intestine. Co-infected mice exhibited fewer and smaller granulomas, which lacked IgG1, SiglecF+ eosinophils, and CD206+ macrophages, correlating with higher worm burdens. Conclusion: Together, these findings highlight the importance of local immune responses to tissue-invading worms and help explain why helminth elimination is frequently more difficult in the complex immune environments found in field settings compared with laboratory conditions.

The intestinal epithelium is in continual flux. It must balance maintaining a healthy microbiota with detecting and destroying intestinal pathogens. Intestinal stem cells (ISCs), which sit in the crypts below the intestinal villi, control this process. Depending on the molecular signals they receive, ISCs rapidly differentiate into the different intestinal epithelial cell subsets, making the intestine a remarkably adaptable organ. However, pathogens can hijack ISC functions to their advantage and establish infections. In this review, we explore the mechanisms used by pathogens to exploit ISCs.

Myxozoans are a monophyletic taxon of approximately 2,400 described species of parasites from the phylum Cnidaria. The recent focus on their negative impacts on fisheries, on their evolution from free-living ancestors, and on their emergence into new fish host populations has stressed the critical need for genomic resources for this parasitic group. Here, we describe the genome assembly and annotation of Myxobolus rasmusseni, an emerging parasite of fathead minnows in Alberta, Canada. The assembly is 174.6 Mb in size, 68% of which is made up of repetitive elements, making it one of the most repetitive animal genomes sequenced to date. Through comparisons to other myxozoans, we show that widespread gene loss, a known phenomenon of this group of parasites, is consistent with closely related species. Additionally, we assembled the M. rasmusseni mitochondrial genome which is nearly twice the size of the typical animal mitochondrial genome yet contains only five of the canonical mitochondrial protein-coding genes and open reading frames not found in other myxozoans. These results add to our understanding of the gene- and genome-level diversity observed in myxozoans.

Haem, which binds iron and oxygen, is essential for parasitic nematode growth. Nematodes lack endogenous haem synthesis pathways and acquire haem from their environment or intracellular symbionts. Genes involved in haem degradation and detoxification have been identified in parasitic nematodes who are either specialised blood feeders (haematophages) or reside in the blood stream. Targeting these genes, so limiting parasite growth and promoting parasite death, provides a new therapeutic avenue against blood feeding parasitic nematodes. Heligmosomoides bakeri , a model intestinal parasitic nematode, has not been considered a blood feeder. Adults live in the intestinal lumen and graze on host tissue. However, the earlier larval stages enter the intestinal tissue, where they grow and moult multiple times, an oxygen demanding process. We have shown that, in vivo , likely through nematode-induced damage, many tissue-dwelling H. bakeri are in close vicinity of red blood cells. During this time, infection induces host anemia. Further, tissue-dwelling H. bakeri that have fed on blood have an increased expression of collagen genes compared to those parasites that had not fed on blood. In vitro , this translates to a growth advantage. Our findings suggest blood feeding is more widespread among nematodes than currently described. We argue that biochemical adaptations previously considered to be limited to blood-feeders are found in other nematodes. Moreover, H. bakeri can serve as a model for studying blood-feeding mechanisms and developing anthelminthic strategies to them.

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, γδ T, CD4⁺ T and CD8⁺ T cells), five organs (small intestine, Peyer’s patches, mesenteric lymph nodes, spleen and liver), and 4 cytokines (IFN©, 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.

[This corrects the article DOI: 10.3389/fimmu.2022.1020056.].

HpARI is an immunomodulatory protein secreted by the intestinal nematode Heligmosomoides polygyrus bakeri , which binds and blocks IL-33. Here, we find that the H. polygyrus bakeri genome contains three HpARI family members and that these have different effects on IL-33-dependent responses in vitro and in vivo , with HpARI1+2 suppressing and HpARI3 amplifying these responses. All HpARIs have sub-nanomolar affinity for mouse IL-33; however, HpARI3 does not block IL-33-ST2 interactions. Instead, HpARI3 stabilizes IL-33, increasing the half-life of the cytokine and amplifying responses to it in vivo . Together, these data show that H. polygyrus bakeri secretes a family of HpARI proteins with both overlapping and distinct functions, comprising a complex immunomodulatory arsenal of host-targeted proteins.

Background The Myxozoa is a group of at least 2,400 endoparasites within the phylum Cnidaria. All myxozoans have greatly reduced in size and morphology compared to free-living members of the phylum. They are best known for causing disease in economically important fish across the world; for example, Myxobolus cerebralis causes whirling disease, which can kill 90% of infected juvenile salmonid fish. In 2017, a new myxozoan species was identified in Alberta. Myxobolus rasmusseni n. sp. causes distinct lesions in fathead minnows, which are ultimately fatal. Here, we sequenced, assembled and analyzed the genome of M. rasmusseni to understand how the parasite interacts with its fish host and identify potential strategies to counter this emerging threat. Results At 185 Mb, the M. rasmusseni genome is the largest myxozoan genome sequenced so far. This large genome size is, in part, due to the high repetitive content; 68% of the genome was interspersed repeats, with the MULE-MuDR transposon covering 18% of the M. rasmusseni genome. Similar to myxozoan genomes, the M. rasmusseni genome has lost many genes well conserved in other eukaryotes. However, we also identified multiple expansions in gene families—serine proteases, hexokinases, and FLYWCH-domain containing proteins—which suggests their functional importance in the parasite. The mitochondrial genome of M. rasmusseni encodes only five of the thirteen protein-coding genes typically found in animals. We found that the mitochondrial gene atp6 was transferred to the nucleus and acquired a mitochondria-targeting signal in M. rasmusseni. Conclusions Our study provides valuable insights into myxozoan biology and identify promising avenues for future research. We also propose that M. rasmusseni is promising myxozoan model to explore host-parasite interactions in these parasites.

HpARI is an immunomodulatory protein secreted by the intestinal nematode Heligmosomoides polygyrus bakeri , which binds and blocks IL-33. Here, we find that the H. polygyrus bakeri genome contains 3 HpARI family members, and that these have different effects on IL-33-dependent responses in vitro and in vivo, with HpARI1+2 suppressing, and HpARI3 amplifying these responses. All HpARIs have sub-nanomolar affinity for mouse IL-33, however HpARI3 does not block IL-33-ST2 interactions. Instead, HpARI3 stabilises IL-33, increasing the half-life of the cytokine and amplifying responses to it in vivo. Together these data show that H. polygyrus bakeri secretes a family of HpARI proteins with both overlapping and distinct functions, comprising a complex immunomodulatory arsenal of host-targeted proteins.