Investigating the immunomodulatory properties of Nippostrongylus brasiliensis; a potential model for Necator americanus
Publication Date
March 15, 2023
Creator
Abstract
Introduction
Necator americanus infection is a significant public health concern, particularly in developing countries. Dendritic cells (DCs) are considered as sentinels of the immune system and act as a link between innate and adaptive immune systems. Following antigen uptake in peripheral tissues, DCs migrate into the regional lymph nodes, where they present peptide antigens derived from pathogens into naïve T cells and guide T cell differentiation towards distinct inflammatory or regulatory phenotypes. The fundamental information about how N. americanus interfaces with immune cells such as DCs and how N. americanus secretions affect DC function and downstream immune responses such as T cell polarisation are still under intensive research. Despite relative successes with the drugs used in treating hookworm infection, there is a high rate of reinfection, and the immune response against hookworms is typically not protective. Therefore, there is a need for a better understanding of the early events involved in the interface between the hookworm and the immune system, which could pave the way for the design of more efficient therapies and vaccines. In a recent study our group have shown exsheathment of N. americanus L3 upon interaction with human immature dendritic cells (iDCs). Intriguingly, these cells did not interact with the exposed infective third-stage larvae (L3) cuticle. However, the exact mechanism underlying such immune evasion has remained elusive. Therefore, characterisation of N. americanus L3 interaction with DCs could provide invaluable insight into mechanism that underpin N. americanus immune evasion and its immune modulatory effects, which could in turn help in the design of new therapeutic strategies. However, a major limitation of working with N. americanus is the availability of viable L3, as they require a human host. Thus, identifying other more readily accessible nematode species that can be used as a surrogate model system for studying human immune responses would greatly facilitate such studies. In this study I used Nippostrongylus brasiliensis parasite as a laboratory model system to investigate physical interaction of N. brasiliensis infective larvae L3 with human DCs and investigated the surface chemical signatures of N. brasiliensis L3 cuticle and its sheath to determine any similarities or differences with N. americanus and whether such molecular signatures could explain the interaction between larvae and DCs. I also investigated the immune modulatory properties of N. brasiliensis infective larvae L3 and their secretion on DCs phenotype and function as well as how these conditioned DCs could influence downstream T cell polarisation. Furthermore, I identified some sugar moieties in the N. brasiliensis L3 secretion similar to those expressed on the surface of larval cuticle and investigated their impact on DCs phenotype and on T cell polarisation.
Results
Our data showed that the exsheathment of N. brasilienis L3 upon the interaction with human iDCs with minimal physical interaction between DCs and the exposed cuticles. I then characterised the chemical composition of larvae sheath and cuticle using Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS). Interestingly, our TOF-SIMS data revealed differences between the surface chemistries of larvae sheath and the cuticle which might be of biological relevance and explain immune evasion by larvae cuticle. For example, the surface of larval cuticle contains phosphatidylglycerol which may inhibit aggregation of DC around larval cuticle and support the migration of infective stage, while the surface of larval sheath express heparan sulphate which could result in the aggregation of DCs and diverse immune defences. Our finding confirm that chemical signatures expressed on N. brasiliensis larval cuticle and its sheath are similar to those signatures expressed on N. americanus larvae previously reported using TOF-SIMS.
Furthermore, DC co-cultured with N. brasiliensis larvae cuticle induced a regulatory DC phenotype characterised by significant production of IL-10, suppression of IL12p70 production in response to LPS as well as induction of regulatory T (Treg) cell differentiation in coculture experiments between conditioned DC and autologous naïve T cells. Given the very limited physical interaction between DCs and larvae, it was reasonable to assume that the observed immune modulatory effects are potentially driven by larvae secretion. To test this hypothesis, similar experiments were carried out using larvae secretions which showed similar effect as infective larvae on DC phenotype, function as well as on T cell polarisation. Further characterisation of larval secretions revealed the presence of sugars moieties such as galactose and N-acetylgalactosamine similar to sugars previously observed on the surface of larval cuticle that could impact DC functions. Intriguingly, this finding highlights the potential role of C-type lectin ligands in mediating the observed immune regulatory effects. Together, these results demonstrate the strong immune regulatory effects of N. brasiliensis infective larvae and their secretions on human DCs and T cells as well as the potential role of CLRs in the process. Galactose and N-acetylgalactosamine (GalNAc) purified from larval secretion induce regulatory DC phenotype as evidenced by a significant downregulation of LPS induced HLA-DR, CD80, CD86 and CD40 expression compared to LPS alone as well as significant upregulation of PDL-1 expression. This was accompanied by significant increase in production of prototypic regulatory cytokine IL-10 and a significant decrease of signature pro-inflammatory cytokine IL-12. Together, these data suggest a regulatory phenotype for DCs treated with galactose and GalNAc in larvae secretions. Furthermore, DCs conditioned with these sugars induced naïve T cell polarisation towards regulatory phenotype that clearly showing the potential role of galactose and GalNAc in immunomodulation.
Conclusion:
Taken together, these observations are in line with previous observations showing similar effects as N. americanus, highlighting the suitability of N. brasiliensis as a model system for investigating early events between human DCs and infective hookworm larvae. In addition, our findings show the potential immunomodulatory properties of N. brasiliensis infective larvae and their secretion in regulating DCs phenotype and skewing immune responses towards regulatory phenotypes. It also provides in understanding of how some sugars present in larval secretion have the ability to modulate immune system. This understanding could pave the way for utilising parasite-derived products in the development of potent treatment for autoimmune or autoinflammatory conditions.
Item Type
ethesis
Thesis Type
PhD
Subjects (LC)
Associated Schools / Departments
School of Life Sciences
eprints ID
71639
UoN Repository URI
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Tahani Hamed Alharbi PhD thesis 2022 final submission.pdf
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