Helminth neuroinfections represent serious medical conditions, but the diversity of the host-parasite interplay within the nervous tissue often remains poorly understood, partially due to the lack of laboratory models. Here, we investigated the neuroinvasion of the mouse spinal cord by Trichobilharzia regenti (Schistosomatidae). Active migration of T. regenti schistosomula through the mouse spinal cord induced motor deficits in hindlimbs but did not affect the general locomotion or working memory. Histological examination of the infected spinal cord revealed eosinophilic meningomyelitis with eosinophil-rich infiltrates entrapping the schistosomula. Flow cytometry and transcriptomic analysis of the spinal cord confirmed massive activation of the host immune response. Of note, we recorded striking upregulation of the major histocompatibility complex II pathway and M2-associated markers, such as arginase or chitinase-like 3. Arginase also dominated the proteins found in the microdissected tissue from the close vicinity of the migrating schistosomula, which unselectively fed on the host nervous tissue. Next, we evaluated the pathological sequelae of T. regenti neuroinvasion. While no demyelination or blood-brain barrier alterations were noticed, our transcriptomic data revealed a remarkable disruption of neurophysiological functions not yet recorded in helminth neuroinfections. We also detected DNA fragmentation at the host-schistosomulum interface, but schistosomula antigens did not affect the viability of neurons and glial cells in vitro. Collectively, altered locomotion, significant disruption of neurophysiological functions, and strong M2 polarization were the most prominent features of T. regenti neuroinvasion, making it a promising candidate for further neuroinfection research. Indeed, understanding the diversity of pathogen-related neuroinflammatory processes is a prerequisite for developing better protective measures, treatment strategies, and diagnostic tools.

• MeSH
• Arginase metabolism   MeSH
• Biomarkers metabolism   MeSH
• Chemokines metabolism   MeSH
• Eosinophils metabolism   MeSH
• Major Histocompatibility Complex MeSH
• Immunity MeSH
• Trematode Infections immunology   metabolism   pathology   MeSH
• Host-Parasite Interactions MeSH
• Spinal Cord parasitology   MeSH
• Disease Models, Animal MeSH
• Mice, Inbred C57BL MeSH
• Mice MeSH
• Neuroglia parasitology   MeSH
• Neurons parasitology   MeSH
• Schistosomatidae immunology   MeSH
• Gene Expression Profiling MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Arginase MeSH
• Biomarkers MeSH
• Chemokines MeSH

BACKGROUND: Avian schistosomes, the causative agents of human cercarial dermatitis (or swimmer's itch), die in mammals but the mechanisms responsible for parasite elimination are unknown. Here we examined the role of reactive nitrogen species, nitric oxide (NO) and peroxynitrite, in the immune response of mice experimentally infected with Trichobilharzia regenti, a model species of avian schistosomes remarkable for its neuropathogenicity. METHODS: Inducible NO synthase (iNOS) was localized by immunohistochemistry in the skin and the spinal cord of mice infected by T. regenti. The impact of iNOS inhibition by aminoguanidine on parasite burden and growth was then evaluated in vivo. The vulnerability of T. regenti schistosomula to NO and peroxynitrite was assessed in vitro by viability assays and electron microscopy. Additionally, the effect of NO on the activity of T. regenti peptidases was tested using a fluorogenic substrate. RESULTS: iNOS was detected around the parasites in the epidermis 8 h post-infection and also in the spinal cord 3 days post-infection (dpi). Inhibition of iNOS resulted in slower parasite growth 3 dpi, but the opposite effect was observed 7 dpi. At the latter time point, moderately increased parasite burden was also noticed in the spinal cord. In vitro, NO did not impair the parasites, but inhibited the activity of T. regenti cathepsins B1.1 and B2, the peptidases essential for parasite migration and digestion. Peroxynitrite severely damaged the surface tegument of the parasites and decreased their viability in vitro, but rather did not participate in parasite clearance in vivo. CONCLUSIONS: Reactive nitrogen species, specifically NO, do not directly kill T. regenti in mice. NO promotes the parasite growth soon after penetration (3 dpi), but prevents it later (7 dpi) when also suspends the parasite migration in the CNS. NO-related disruption of the parasite proteolytic machinery is partly responsible for this effect.

• Keywords
• 3-Nitrotyrosine, Cathepsin B, Nitric oxide, Nitric oxide synthase, Peroxynitrite, Schistosomatidae, Trichobilharzia,
• MeSH
• Central Nervous System parasitology   MeSH
• Guanidines pharmacology   MeSH
• Trematode Infections drug therapy   MeSH
• Skin parasitology   MeSH
• Peroxynitrous Acid pharmacology   MeSH
• Humans MeSH
• Spinal Cord parasitology   MeSH
• Mice MeSH
• Nitric Oxide pharmacology   MeSH
• Peptide Hydrolases drug effects   metabolism   MeSH
• Helminth Proteins drug effects   metabolism   MeSH
• Birds parasitology   MeSH
• Schistosoma drug effects   growth & development   pathogenicity   MeSH
• Schistosomatidae drug effects   growth & development   pathogenicity   MeSH
• Schistosomiasis drug therapy   MeSH
• Nitric Oxide Synthase drug effects   metabolism   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Guanidines MeSH
• Peroxynitrous Acid MeSH
• Nitric Oxide MeSH
• pimagedine MeSH Browser
• Peptide Hydrolases MeSH
• Helminth Proteins MeSH
• Nitric Oxide Synthase MeSH

BACKGROUND: Helminth neuroinfections represent a serious health problem, but host immune mechanisms in the nervous tissue often remain undiscovered. This study aims at in vitro characterization of the response of murine astrocytes and microglia exposed to Trichobilharzia regenti which is a neuropathogenic schistosome migrating through the central nervous system of vertebrate hosts. Trichobilharzia regenti infects birds and mammals in which it may cause severe neuromotor impairment. This study was focused on astrocytes and microglia as these are immunocompetent cells of the nervous tissue and their activation was recently observed in T. regenti-infected mice. RESULTS: Primary astrocytes and microglia were exposed to several stimulants of T. regenti origin. Living schistosomulum-like stages caused increased secretion of IL-6 in astrocyte cultures, but no changes in nitric oxide (NO) production were noticed. Nevertheless, elevated parasite mortality was observed in these cultures. Soluble fraction of the homogenate from schistosomulum-like stages stimulated NO production by both astrocytes and microglia, and IL-6 and TNF-α secretion in astrocyte cultures. Similarly, recombinant cathepsins B1.1 and B2 triggered IL-6 and TNF-α release in astrocyte and microglia cultures, and NO production in astrocyte cultures. Stimulants had no effect on production of anti-inflammatory cytokines IL-10 or TGF-β1. CONCLUSIONS: Both astrocytes and microglia are capable of production of NO and proinflammatory cytokines IL-6 and TNF-α following in vitro exposure to various stimulants of T. regenti origin. Astrocytes might be involved in triggering the tissue inflammation in the early phase of T. regenti infection and are proposed to participate in destruction of migrating schistosomula. However, NO is not the major factor responsible for parasite damage. Both astrocytes and microglia can be responsible for the nervous tissue pathology and maintaining the ongoing inflammation since they are a source of NO and proinflammatory cytokines which are released after exposure to parasite antigens.

• Keywords
• Anti-inflammatory cytokines, Astrocytes, Avian schistosome, Cathepsin B, Microglia, Neuroinfection, Nitric oxide, Proinflammatory cytokines, Trichobilharzia regenti,
• MeSH
• Astrocytes immunology   parasitology   MeSH
• Interleukin-6 metabolism   MeSH
• Cells, Cultured MeSH
• Mice MeSH
• Neuroglia immunology   parasitology   MeSH
• Nitric Oxide metabolism   MeSH
• Schistosomatidae immunology   MeSH
• Tumor Necrosis Factor-alpha metabolism   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• interleukin-6, mouse MeSH Browser
• Interleukin-6 MeSH
• Nitric Oxide MeSH
• Tumor Necrosis Factor-alpha MeSH