Recognition of Schistosoma mansoni egg-expressed ovalbumin by T cell receptor transgenic mice

https://doi.org/10.1016/j.exppara.2019.107767Get rights and content

Highlights

  • We showed, by western blot & RT-PCR, that S.mansoni eggs can express chicken ovalbumin following lenti viral transduction.

  • OVA transgenic S. mansoni eggs induce proliferation of antigen-specific OT-II T cells & expression of signature cytokines.

  • This work will allow the unravelling of the mechanisms used by the parasite to manipulate the immune system in vivo.

Abstract

Schistosoma mansoni eggs can influence immune responses directed at them, and the mechanisms by which this is achieved are being unravelled. Going towards, developing effective tools for the study of how S. mansoni influences naïve T cells, we have developed S. mansoni eggs expressing chicken ovalbumin (OVA), using a lentiviral transduction system. Indeed, such a parasite could be used in conjunction with cells from OT-II transgenic mice as a source of naïve, antigen-specific T cells. The expression of the transgenic protein was confirmed by real-time RT-PCR of OVA-specific mRNA and western blotting using polyclonal antibodies specific for OVA. T cells from OT-II transgenic mice expressing a T cell receptor specific for the OVA323-339 peptide recognised the OVA-transduced S. mansoni eggs. Using flow cytometry on CFSE-labelled OT-II splenocytes, we demonstrated that OVA-transduced eggs elicit higher OT-II proliferative responses than untransduced eggs. The OT-II T cells also produced TNF-α and IFN-γ following exposure to OVA-transduced eggs. In addition, moderate amounts of IL-6 and IL-17A were also detected. In contrast, no IL-10, IL-4 and IL-2 were detected in cultures, whether the cells were stimulated with transduced or untransduced eggs. Thus, the cytokine signatures showed the transfected eggs induced predominantly a Th1 response, with a small amount of IL-6 and IL-17.

Introduction

Schistosomiasis, a parasitic disease caused by trematodes or digenetic blood flukes, is one of the most devastating tropical diseases. It is endemic in 74 countries and affects more than 200 million people worldwide, with 85% of patients living in Africa [Chitsulo et al., 2017]. Regular and periodic chemotherapy of at-risk groups with praziquantel, with potency against the Schistosoma adult parasite, is the only available intervention strategy [WHO, 2015]. As a result, the global and regional occurrence of the diseases has declined in the past few decades. However, elimination of the disease remains a global challenge [WHO, 2015]. While an effective vaccine is not yet available, the recent discovery of specific vaccine antigens has shown promise. Drug treatment targeting the parasite and control of the arthropod vector combined with vaccines might offer a long-term solution (Moreno-Cid et al., 2013; Sinden, 2017), despite genetic variation among parasitic strains, which could affect vaccine coverage (Sheerin et al., 2017). However, induction of effective protective immunity remains out of reach at least in part because of the ability of the parasite to modulate immune response.

Therefore, understanding how the parasite persists in the face of robust stimulation of the host immune system is one of the most important aspects in the study of host-parasite interactions [Hagen et al., 2015]. Indeed, S. mansoni, is known to have specific tactics to manipulate the host immune response in order to ensure its survival in the host [Bergquist, 1995]. Modulating the immune system at a molecular level via, in particular, soluble egg antigens (SEAs) is one of the key strategies for S. mansoni to compromise host immunity [Kane et al., 2008]. However, the mechanism of this specific immunomodulation remains elusive, particularly in vivo [Fallon and Antonio, 2006]. The immunomodulatory potential of S. mansoni eggs at the onset of chronic infection, is well documented and characterized by a Th2 polarized immune response [Pearce et al., 2004]. This Th2 response is associated with down-regulation of the initial Th1 or pro-inflammatory responses to migrating cercaria and leads to granuloma formation [Brunet et al., 1997; Fallon et al., 2000]. Many SEAs have been identified in S. mansoni, including omega-1 now understood to drive Th2-polarized responses, through interaction with dendritic cells (DCs). This protein plays an important role in switching the Th1 response into a Th2 response through inhibition of IL-12 production [Everts et al., 2009; Steinfelder et al., 2001]. Moreover, other SEAs, such as, IPSE/α-1, trigger Ig-E-driven IL-4 secretion by basophils and induces alternatively activated macrophages and, thus, Th2-polarized responses [Donnelly et al., 2008]. Kappa-5 is another immunomodulatory SEA present in S. mansoni.

In the present study, we utilised S. mansoni-expressed chicken ovalbumin (OVA), to study the immune response of parasite-associated antigens in inducing biased Th responses in naïve T cells. OVA being a model antigen avoids the induction of biased immune response and is ideal for such investigations as it is difficult to exclude that parasite-derived antigens have intrinsic biases selected as a result of prolonged evolutionary pressures. The expression of OVA in the parasite therefore helps to elucidate the immunomodulatory properties of the soluble egg antigens of the parasite egg and, using the expressed protein as a neutral antigen, we are able to further characterise functions of specific SEAs. As a first step, demonstrating that T cell receptor transgenic mice (OT-II mice) known for having higher frequency of CD4+ T cell receptors that recognise OVA, as a source of naïve CD4+ T cells that can recognise S. mansoni expressed OVA, is essential. Here we show that, OT-II cells respond to this antigen by proliferating and producing key cytokines in vitro.

Section snippets

Experimental mice and maintenance of the S. mansoni life cycle

Six- to eight-week-old female BALB/c and OT-II mice were purchased from the Walter and Eliza Hall Institute of Medical Research (WEHI) and were used in the present study to maintain the life cycle of S. mansoni and as a source of naïve OT-II T cells, respectively. All the experiments related with mice were conducted after getting an approval from the Animal Ethical Committee of the University of Melbourne (Ethics ID: 1312952). Snails (Biomphlaria glabrata, NMRI strain), an intermediate host of

Optimisation of OVA for expression and secretion in S. mansoni eggs following lentiviral transduction

The first 47-amino acid signal peptide sequence of original OVA was replaced by the 23-amino acid of S. mansoni ω-1 signal sequence. And 6-histidine sequence was added at the C-terminal end of the optimized sequence. Two restriction sites, SpeI at the N-terminal end and NotI at the C-terminal end were included to the sequence. After the sequence was synthesized commercially by GenScript (NJ, USA), the gene was cloned in to the pGIPZ_CMV_mCherry via SpeI and NotI replacing mCherry to produce

Discussion

As a result of the complex biology of the schistosome parasite, generation of a transgenic parasite eggs has been challenging. However, recently, introduction of foreign genes was achieved using lentiviruses as a vector [Hagen et al., 2014]. Lentiviral vectors, which are modified from the type 1 human immunodeficiency virus (HIV-1), have become the main tool for gene-delivery to mammalian cells and are known for their important features of mediating strong transduction and stable expression

Acknowledgements

We are grateful to Melbourne International Research Scholarship for research training sponsorship.

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  • Cited by (0)

    1

    Both authors contributed equally.

    2

    Current address: Department of Life Sciences, Imperial College London, London, SW7 2AZ, UK.

    3

    Current address: College of Science, Health and Engineering, La Trobe University, Victoria, 3086.

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