Biochemical and Biophysical Research Communications
The tick saliva immunosuppressor, Salp15, contributes to Th17-induced pathology during Experimental Autoimmune Encephalomyelitis
Research highlights
► Treatment with the immunosuppressive protein, Salp15, during induction of murine EAE exacerbates pathology. ► Salp15 does not prevent the activation of pathogenic T cells in EAE-induced mice. ► Th17 differentiation is increased in EAE-induced mice treated with Salp15. ► In vitro, Salp15 inhibits IL-2 production and enhances Th17 differentiation in the absence of TGFβ.
Introduction
The tick salivary protein Salp15 inhibits the activation of CD4+ T cells during their encounter with cognate antigen by repressing the production of the autocrine growth factor IL-2 [1]. The effect of Salp15 is mediated by its interaction with the T cell co-receptor, CD4 [2]. The activity of Salp15 requires its carboxyl terminal residues and occurs through its interaction with the first two most-extracellular domains of CD4 [2], [3]. The interaction results in a conformational change of CD4 that impedes the proper activation of the Src kinase, Lck [3], leading to the inhibition of early signaling cascades [2], [4]. In vivo, Salp15 prevents the development of acute asthma in ovalbumin-induced mice [5] and the development of antibody and delayed-type sensitivity responses in KLH-immunized animals [1]. Thus, Salp15 has potential beneficial use in conditions in which CD4+ T cells are involved, including autoimmune diseases in which CD4+ T cells are major players.
Multiple sclerosis is a chronic inflammatory disease that affects the central nervous system. The inflammation associated with the disease is believed to be the consequence of the activation of inflammatory CD4+ T cells. Mice can also develop a demyelinating inflammatory disease of the central nervous system (CNS) known as Experimental Autoimmune Encephalomyelitis (EAE) that mimics MS [6]. The mice, when immunized with a specific peptide from the myelin proteolipid protein (PLP) or Myelin Basic Protein (MBP) [7], [8], [9] develop an MS-like syndrome with a course that is similar to that found in humans [10]. The inflammatory response associated with disease progression is caused by T helper cells that secrete interleukin 17 (IL-17A), known as Th17 cells, in combination with IFNγ-secreting Th1 cells [11], [12], [13], [14]. Th17 cells participate directly in the development and pathogenesis of EAE [15]. Thus, the transfer of IL-17-producing T cells results in severe EAE [16] and mice deficient in IL-17 markedly suppress the development of EAE [15]. In addition, mice treated with a neutralizing monoclonal antibody specific for IL-17 demonstrated reduced CNS autoimmune inflammation [16].
In mice, the differentiation of Th17 cells requires the presence of transforming growth factor (TGF) β and the pleiotropic cytokine IL-6 [17], [18], [19]. In order for a Th17 response to prevail, the heterodimeric cytokine, IL-23, which shares the p40 subunit with IL-12, must be present to sustain Th17 cell survival and maintenance [16]. Th17 cell differentiation requires the orphan nuclear receptors, ROR-γt and RORα, two specific transcriptional factors that are selectively expressed in Th17 cells [20], [21]. The importance of these transcriptional factors in the development of Th17 cells is underlined by experiments showing that RORγt/RORα double deficiency completely abrogates Th17 differentiation in vitro [21]. Furthermore, RORγt/RORα deficient mice do not develop EAE [21].
Because Salp15 is able to prevent the activation of antigen-specific CD4+ T cells in vivo [1], [5] and prevent inflammation in a murine model of asthma [5], we postulated that the administration of the protein during the induction of EAE in mice would prevent the generation of autoreactive T cells and the development of CNS inflammation. Our results show that surprisingly, Salp15 induces the increased differentiation of Th17 effector cells both in vivo and in vitro. Our results suggest that immunosuppressive agents can mimic the role of TGFβ during the differentiation of Th17 cells through the repression of the production of IL-2 during the differentiation process.
Section snippets
Mice, peptide and induction of EAE
Female SJL/J mice 8 week old were purchased from Jackson laboratories (Bar Harbor, ME). The mice in groups of 3–5 were injected subcutaneously in both flanks with 100 μg of PLP peptide 139–151 (HSLGKWLGHPDKF) (Research Genetics, Huntsville, AL). The original cysteine has been substituted by serine for stability purposes. This change does not induce any alteration in the antigenicity of the peptide [22]. EAE was induced by immunizing the mice with 100 μg of the peptide dissolved in an emulsion of
Treatment with Salp15 during EAE induction results in increased pathology
Murine Experimental Autoimmune Encephalomyelitis is mediated by the activation of CD4+ T cells that respond to self antigens present in the myelin sheath. Salp15 has been shown to prevent the development of ovalbumin-induced asthma in mice [5] and of KLH-specific antibody and DTH responses [1] through the specific inhibition of CD4+ T cell activation. We thus hypothesized that the administration of the tick salivary protein during induction of murine EAE would prevent the activation of
Acknowledgments
This work was supported by the NINDS/NIH grant R21NS048433.
We thank Dr. Cory Teuscher for his advice.
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Cited by (11)
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2017, Veterinary ParasitologyCitation Excerpt :During tick bite and blood feeding, ticks are exposed to host innate immune responses and the complement system and protect themselves from host immunoglobulin- and T cell-mediated immune responses to ensure blood feeding success (Kazimirova and Stibraniova, 2013). Accordingly, Salp 15 inhibits T cell activation and IL-2 production by binding to CD4 (Juncadella et al., 2010) and a Salp 16-like molecule attenuates the oxidative burst of activated bovine neutrophils and inhibits neutrophil migration induced by interleukin-8 (IL-8) (Hidano et al., 2014). Iris-1 from the salivary glands of Ixodes persulcatus inhibits T cell proliferation and IFN-γ production in bovine peripheral blood mononuclear cells (PBMCs) (Toyomane et al., 2016).
Identification and partial characterization of a Salp15 homolog from Ixodes ricinus
2014, Ticks and Tick-borne DiseasesCitation Excerpt :Moreover, Salp15 protein has been shown to inhibit a Toll-like receptor and the B. burgdorferi-induced production of pro-inflammatory cytokines by dendritic cells and dendritic cell-induced T-cell activation (Hovius et al., 2008a,b). Furthermore, Salp15 induced Th17 cell differentiation in vivo and in vitro (Juncadella et al., 2010). In this study, we identified a novel homolog of Salp15 protein in I. ricinus, which we named I. ricinus Salp15-like protein, and we demonstrated that the recombinant I. ricinus Salp15-like protein suppressed IL-10 production from LPS-stimulated PBMCs in a dose-dependent manner.
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- 1
Present address: Carter Center for Immunology, University of Virginia, Charlottesville, VA.
- 2
Present address: Department of Biology, University of North Carolina at Charlotte, Charlotte, NC, United States.
- 3
Present address: Infectious Disease Laboratory. National Naval Medical Center, Bethesda, MD 20889, United States.
- 4
Present address: Department of Biochemistry and Molecular Biology, Universidad de León, León, Spain.