Elsevier

Cytokine

Volume 35, Issues 5–6, September 2006, Pages 235-246
Cytokine

Blockade of TLR9 agonist-induced type I interferons promotes inflammatory cytokine IFN-γ and IL-17 secretion by activated human PBMC

https://doi.org/10.1016/j.cyto.2006.09.001Get rights and content

Abstract

Type I interferons (IFN) (IFN-α/β) are recognized as both inhibitors and effectors of autoimmune disease. In multiple sclerosis, IFN-β therapy appears beneficial, in part, due to its suppression of autoimmune inflammatory Th cell responses. In contrast, in systemic lupus erythematosus (SLE) triggering of plasmacytoid DC (pDC) Toll-like receptors (TLRs) by autoimmune complexes (autoICs) results in circulating type I IFN that appear to promote disease by driving autoantigen presentation and autoantibody production. To investigate how pDC-derived type I IFN might regulate Th cells in SLE, we examined a model in which sustained pDC stimulation by autoICs is mimicked by pretreating normal human PBMC with TLR9 agonist, CpG-A. Subsequently, PBMC Th cells are activated with superantigen, and APC are activated with CD40L. The role of CpG-A/TLR9-induced type I IFN in regulating PBMC is determined by blocking with virus-derived soluble type I IFN receptor, B18R. In summary, pretreatment with either rhIFN-α/β or CpG-A inhibits PBMC secretion of superantigen-induced IFN-γ and IL-17, and CD40L-induced IL-12p70 and IL-23. B18R prevents these effects. Data indicate that CpG-A-induced type I IFN inhibit IL-12p70-dependent PBMC IFN-γ secretion by enhancing IL-10. Our results suggest that in SLE, circulating type I IFN may potentially act to inhibit inflammatory cytokine secretion.

Introduction

Type I interferons (IFN) (IFN-α/β) are increasingly recognized as immune modulators that can inhibit or promote autoimmune diseases, including multiple sclerosis (MS), systemic lupus erythematosus (SLE), rheumatoid arthritis, and diabetes[61]. In SLE, a central role for type I IFN, in particular IFN-α, in disease pathogenesis is strongly indicated by studies of SLE patients and murine models of lupus (reviewed in [8]). In patients with active SLE, levels of IFN-α and expression of IFN-responsive genes are often elevated and correlated with the severity of disease [7], [11], [12], [34], [54]. Moreover, IFN-α therapy is known to induce clinical SLE [49]. Finally, in certain murine models of SLE, genetic type I IFN receptor deficiency suppresses autoimmune disease [37], [56].

It is now known that the specific source of IFN-α in SLE is the plasmacytoid dendritic cell (pDC) [55]. A current model of SLE envisions that engagement of pDC Toll-like receptors (TLRs) by circulating nucleic acid-containing autoimmune complexes (autoICs) stimulates pDC secretion of IFN-α. Subsequently, IFN-α acts to drive monocyte differentiation and immature myeloid DC maturation which, in turn, leads to the presentation of nuclear self-antigen to autoreactive T helper (Th) cells and breaking of tolerance[51]. Activated Th cells then help autoreactive B cells differentiate into autoantibody-producing plasma cells. In SLE, the effects of pathogenic autoantibodies and autoIC deposition results in inflammation and tissue damage, with release of cell debris that may provide a new source of self antigen to perpetuate the disease[41]. Currently, a major area of interest in designing new SLE therapies is on breaking the cycle of autoimmune disease by blocking the activity of circulating, pDC-derived type I IFN [51], [58].

The direct effects of inflammatory Th1-type cells also appear to contribute to autoimmune-mediated tissue injury in SLE [3], [9], [15], [61], [62], [63]. A Th1 predominance has been reported in some SLE patients, as indicated by increased systemic and/or local levels of the inflammatory cytokine IFN-γ, and the pro-inflammatory IFN-γ-inducers, IL-12 p70, and IL-18 [6], [15], [28], [52], [53], [64], [70], [71]. In addition, the activity of inflammatory Th1 cells is strongly implicated in mediating certain forms of lupus, including lupus glomerular nephritis, and cutaneous, and CNS lupus [2], [15], [17], [33], [66], [70].

The role of pDC-derived type I IFN in influencing autoimmune inflammatory Th cell responses in SLE is unknown. Type I IFN can have both positive and negative regulatory effects on inflammatory Th cell functions. Thus, although type I IFN are often considered to be promoters of anti-viral Th1-mediated immunity [42], [57], we and others have demonstrated that these IFN can act as potent inhibitors of Th1-mediated inflammation, and have shown that the basis for this effect is, at least in part, through their regulation of myeloid DC function [13], [22], [24], [44], [45], [47], [48], [67]. Indeed, it is this latter, Th1-inhibitory effect that appears to contribute to the beneficial effects of IFN-β therapy in the treatment of relapsing remitting MS, an inflammatory Th1-mediated autoimmune disease [14], [32].

The mechanisms involved in the opposing effects of type I IFN on human inflammatory Th cell-mediated immunity are not well understood, and they are the focus of our laboratory’s research. We observe that type I IFN regulate human myeloid DC expression of pro-inflammatory IFN-γ-inducing cytokines, and that depending on the timing of exposure, type I IFN can either promote or inhibit the differentiation of human naïve Th cells into IFN-γ-secreting Th1-type effector cells [67], [47]. Based on these and other findings, we hypothesized that in SLE, constant triggering of pDC TLR9 by autoICs results in high levels of circulating type I IFN that act to inhibit Th cell-mediated autoimmune inflammation. To explore this hypothesis, we developed a unique model of human PBMC stimulation to examine the effects of TLR9-induced type I IFN on PBMC cytokine secretion. In this model, normal PBMC are pretreated with the TLR9 agonist, CpG-A, and Th cells within the PBMC are subsequently activated with superantigen, while APC are activated with CD40L. Our results indicate that when pDC TLR9 triggering precedes APC cell activation and Th activation, the overall effect is to inhibit PBMC secretion of, respectively, the pro-inflammatory cytokines, IL-12 p70 and IL-23, and the inflammatory cytokines, IFN-γ and IL-17. Moreover, our data also indicate that this inhibitory effect is specifically mediated by pDC TLR9 agonist-induced type I IFN.

Section snippets

Cytokines and other cell culture reagents

The following recombinant human (rh) cytokines and other molecules were used during cell culture: Staphylococcal Enterotoxin A (SEA) (Toxin Technology; Sarasota, FL); rhIFN-β (Avonex; Biogen Idec, Cambridge, MA), rhIFN-α-a2 (Biosource) rhIFN-γ (BD/Pharmingen; San Diego, CA); rh interleukin (IL)-12 p70 (Hoffman-La Roche; Nutley, NJ), rhIL-23 (R&D Systems; Minneapolis, MN), and rhIL-10 (BD/Pharmingen); CpG-A, oligodeoxynucleotide (ODN) 2336 (Coley Pharmaceuticals, Wellesley, MA); B18R

A model of human PBMC stimulation

We developed a unique model of human PBMC stimulation in order to examine how, in SLE and other autoimmune diseases, constant triggering of pDC TLR9 by autoICs might regulate Th cell autoimmune inflammatory responses. In this model (see Fig. 6A), sustained pDC TLR9 stimulation by circulating SLE autoICs is mimicked by pretreating normal PBMC for 18 h with the pDC TLR9 ligand, CpG-A. Subsequently, stimulation of autoreactive Th cells with nuclear self antigen is mimicked by using the bacterial

Discussion

The studies presented herein demonstrate that pre-exposure to TLR9 agonist-induced type I IFN can inhibit activated PBMC secretion of the inflammatory cytokines, IFN-γ and IL-17, and pro-inflammatory cytokines, IL-12 p70 and IL-23. Our results indicate that type I IFN-mediated inhibition of PBMC IFN-γ secretion is largely due to a suppression of IFN-γ secretion by activated Th cells. Moreover, they suggest that inhibition of PBMC IFN-γ is mediated by a negative regulatory effect of type I IFN

Acknowledgements

The authors thank Dr. Ann Marshak Rothstein, and Dr. Robert Lafyatis for their helpful discussions and critical reviews of the manuscript.

References (68)

  • H. Liptakova et al.

    Analysis of an interaction between the soluble vaccinia virus-coded type I interferon (IFN)-receptor and human IFN-alpha1 and IFN-alpha2

    Virology

    (1997)
  • B.L. McRae et al.

    Interferon-alpha and -beta inhibit the in vitro differentiation of immunocompetent human dendritic cells from CD14(+) precursors

    Blood

    (2000)
  • L. Ronnblom et al.

    An etiopathogenic role for the type I IFN system in SLE

    Trends Immunol

    (2001)
  • L. Ronnblom et al.

    The natural interferon-alpha producing cells in systemic lupus erythematosus

    Hum Immunol

    (2002)
  • J.A. Symons et al.

    Vaccinia virus encodes a soluble type I interferon receptor of novel structure and broad species specificity

    Cell

    (1995)
  • J.M. van Seventer et al.

    Interferon-beta differentially regulates expression of the IL-12 family members p35, p40, p19 and EBI3 in activated human dendritic cells

    J Neuroimmunol

    (2002)
  • M. Akahoshi et al.

    Th1/Th2 balance of peripheral T helper cells in systemic lupus erythematosus

    Arthritis Rheum

    (1999)
  • M. Akahoshi et al.

    Th1/Th2 balance of peripheral T helper cells in systemic lupus erythematosus

    Arthritis Rheum

    (1999)
  • A. Alcami et al.

    The vaccinia virus soluble alpha/beta interferon (IFN) receptor binds to the cell surface and protects cells from the antiviral effects of IFN

    J Virol

    (2000)
  • P. Amerio et al.

    Increased IL-18 in patients with systemic lupus erythematosus: relations with Th-1, Th-2, pro-inflammatory cytokines and disease activity. IL-18 is a marker of disease activity but does not correlate with pro-inflammatory cytokines

    Clin Exp Rheumatol

    (2002)
  • E.C. Baechler et al.

    Interferon-inducible gene expression signature in peripheral blood cells of patients with severe lupus

    Proc Natl Acad Sci USA

    (2003)
  • D. Balomenos et al.

    Interferon-gamma is required for lupus-like disease and lympho accumulation in MRL-lpr mice

    J Clin Invest

    (1998)
  • E.J. Bartholome et al.

    Interferon-beta inhibits Th1 responses at the dendritic cell level. Relevance to multiple sclerosis

    Acta Neurol Belg

    (1999)
  • A.A. Bengtsson et al.

    Activation of type I interferon system in systemic lupus erythematosus correlates with disease activity but not with antiretroviral antibodies

    Lupus

    (2000)
  • L. Bennett et al.

    Interferon and granulopoiesis signatures in systemic lupus erythematosus blood

    J Exp Med

    (2003)
  • A.A. Byrnes et al.

    Type I interferons and IL-12: convergence and cross-regulation among mediators of cellular immunity

    Eur J Immunol

    (2001)
  • A.A. Byrnes et al.

    Interferon-beta therapy for multiple sclerosis induces reciprocal changes in interleukin-12 and interleukin-10 production

    Ann Neurol

    (2002)
  • N. Calvani et al.

    Up-regulation of IL-18 and predominance of a Th1 immune response is a hallmark of lupus nephritis

    Clin Exp Immunol

    (2004)
  • R.S. Chu et al.

    CpG oligodeoxynucleotides act as adjuvants that switch on T helper 1 (Th1) immunity

    J Exp Med

    (1997)
  • L.P. Cousens et al.

    Interferon-alpha/beta inhibition of interleukin 12 and interferon-gamma production in vitro and endogenously during viral infection

    Proc Natl Acad Sci USA

    (1997)
  • D.J. Cua et al.

    Interleukin-23 rather than interleukin-12 is the critical cytokine for autoimmune inflammation of the brain

    Nature

    (2003)
  • M. Dalod et al.

    Interferon alpha/beta and interleukin 12 responses to viral infections: pathways regulating dendritic cell cytokine expression in vivo

    J Exp Med

    (2002)
  • T.A. Fehniger et al.

    Differential cytokine and chemokine gene expression by human NK cells following activation with IL-18 or IL-15 in combination with IL-12: implications for the innate immune response

    J Immunol

    (1999)
  • L.E. Harrington et al.

    Interleukin 17-producing CD4+ effector T cells develop via a lineage distinct from the T helper type 1 and 2 lineages

    Nat Immunol

    (2005)
  • Cited by (0)

    This research was funded by NIH/NIAID Grants R01AI44209 to G.A.v.S., and R21A1061433 to G.A.v.S. and J.M.v.S.

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