Systemic lupus erythematosus (SLE) is a severe and incurable autoimmune disease characterized by chronic activation of plasmacytoid dendritic cells (pDCs) and production of autoantibodies against nuclear self-antigens by hyperreactive B cells. Neutrophils are also implicated in disease pathogenesis; however, the mechanisms involved are unknown. Here, we identified in the sera of SLE patients immunogenic complexes composed of neutrophil-derived antimicrobial peptides and self-DNA. These complexes were produced by activated neutrophils in the form of web-like structures known as neutrophil extracellular traps (NETs) and efficiently triggered innate pDC activation via Toll-like receptor 9 (TLR9). SLE patients were found to develop autoantibodies to both the self-DNA and antimicrobial peptides in NETs, indicating that these complexes could also serve as autoantigens to trigger B cell activation. Circulating neutrophils from SLE patients released more NETs than those from healthy donors; this was further stimulated by the antimicrobial autoantibodies, suggesting a mechanism for the chronic release of immunogenic complexes in SLE. Our data establish a link between neutrophils, pDC activation, and autoimmunity in SLE, providing new potential targets for the treatment of this devastating disease.

Psoriasis is a common T-cell-mediated skin disease with 2-3% prevalence worldwide. Psoriasis is considered to be an autoimmune disease, but the precise nature of the autoantigens triggering T-cell activation remains poorly understood. Here we find that two-thirds of patients with moderate-to-severe plaque psoriasis harbour CD4 þ and/or CD8 þ T cells specific for LL37, an antimicrobial peptide (AMP) overexpressed in psoriatic skin and reported to trigger activation of innate immune cells. LL37-specific T cells produce IFN-g, and CD4 þ T cells also produce Th17 cytokines. LL37-specific T cells can infiltrate lesional skin and may be tracked in patients blood by tetramers staining. Presence of circulating LL37-specific T cells correlates significantly with disease activity, suggesting a contribution to disease pathogenesis. Thus, we uncover a role of LL37 as a T-cell autoantigen in psoriasis and provide evidence for a role of AMPs in both innate and adaptive immune cell activation.

CD38, an ectoenzyme and a signaling receptor, is a novel marker of human mature monocyte-derived dendritic cells (MDDCs). The working hypothesis is that CD38 is not only a marker but also contributes to functions specifically gained by MDDCs with maturation. This was tested by assessing the role(s) of CD38 after signaling with agonistic anti-CD38 monoclonal antibodies or by blocking the interactions taking place between CD38 and CD31, its counterreceptor. IntroductionCD38 is a pleiotropic cell surface molecule acting as an ectoenzyme and a receptor. The enzymatic activity ends in the synthesis of Ca 2ϩ -mobilizing metabolites (ie, ADP-ribose [ADPR], nicotinic acid adenine dinucleotide phosphate [NAADP], and cyclic ADP-ribose [cADPR]) involved in the regulation of calcium-dependent calcium release. 1,2 CD38 has a unique pattern of surface expression among cells of the human immune system, being present on lymphoid and myeloid progenitors, lost during differentiation, and re-expressed at high density in activated T, B, and natural killer (NK) cells. 3,4 The molecule shows a broad distribution in different tissues. 5 CD38 ligation in immune cells delivers activation signals and induces cytokine production and secretion by T, 6 B, 7 and NK cells 8 and monocytes. 9 CD38 also regulates cell viability by preventing human germinal center B cells from undergoing apoptosis 10 and contributing to increased survival of B-cell chronic lymphocytic leukemia (B-CLL) cells. 11 This panoply of different functional roles may be explained considering some nonconventional features of CD38 as a receptor. The intrinsic ineptitude of CD38 to transduce signals is overcome by working in physical and functional associations with specialized signaling molecules, such as T-cell receptor on T cells, 12-14 B-cell receptor on B cells, 15,16 and CD16 on NK cells. 17 CD38 can sustain adhesion and rolling of CD38 ϩ lymphocytes on endothelial cells through interaction with CD31 (identified as a specific counterreceptor 18 ), suggesting its possible role in lymphocyte trafficking. 19 All the signals mediated by monoclonal antibody (mAb) ligation of CD38 can be reproduced by its interaction with CD31.In murine models, CD38 is involved in chemotaxis and transendothelial migration of both polymorphonuclear leukocytes (PMNs) and dendritic cells (DCs) and this function requires its enzymatic activities. 20,21 Consequently, CD38 knockout mice have impaired capacity to respond to infections. 20 The evaluation of the expression of the molecule also has applications in clinical diagnosis, such as in AIDS (where CD38 is one of the earliest indicators of infection 22 ) and B-CLL (where the expression is generally associated with poor prognosis 15 ). Autoantibodies specific for CD38 are found in diabetes and thyroid disorders. [23][24][25][26] The agonistic properties of these autoantibodies envisage pathogenic role(s) in these diseases.We recently reported a pulsatile pattern of surface CD38 expression in human monocyte-derived dendritic cells (MDDCs). 27 ...

Systemic sclerosis (SSc) is a chronic autoimmune disease characterized by fibrosis and vasculopathy. CXCL4 represents an early serum biomarker of severe SSc and likely contributes to inflammation via chemokine signaling pathways, but the exact role of CXCL4 in SSc pathogenesis is unclear. Here, we elucidate an unanticipated mechanism for CXCL4-mediated immune amplification in SSc, in which CXCL4 organizes “self” and microbial DNA into liquid crystalline immune complexes that amplify TLR9-mediated plasmacytoid dendritic cell (pDC)-hyperactivation and interferon-α production. Surprisingly, this activity does not require CXCR3, the CXCL4 receptor. Importantly, we find that CXCL4-DNA complexes are present in vivo and correlate with type I interferon (IFN-I) in SSc blood, and that CXCL4-positive skin pDCs coexpress IFN-I-related genes. Thus, we establish a direct link between CXCL4 overexpression and the IFN-I-gene signature in SSc and outline a paradigm in which chemokines can drastically modulate innate immune receptors without being direct agonists.

Double-stranded DNA (dsDNA) can trigger the production of type I interferon (IFN) in plasmacytoid dendritic cells (pDCs) by binding to endosomal Toll-like receptor-9 (TLR9; refs 1-5). It is also known that the formation of DNA-antimicrobial peptide complexes can lead to autoimmune diseases via amplification of pDC activation. Here, by combining X-ray scattering, computer simulations, microscopy and measurements of pDC IFN production, we demonstrate that a broad range of antimicrobial peptides and other cationic molecules cause similar effects, and elucidate the criteria for amplification. TLR9 activation depends on both the inter-DNA spacing and the multiplicity of parallel DNA ligands in the self-assembled liquid-crystalline complex. Complexes with a grill-like arrangement of DNA at the optimum spacing can interlock with multiple TLR9 like a zipper, leading to multivalent electrostatic interactions that drastically amplify binding and thereby the immune response. Our results suggest that TLR9 activation and thus TLR9-mediated immune responses can be modulated deterministically.

Lupus erythematosus (LE) patients develop autoantibodies that form circulating immune complexes (ICs) with extracellular self-nucleic acids. These ICs are deposited into peripheral tissues, where they trigger detrimental organ inflammation. Recent evidence suggests that ICs contain LL37-DNA complexes derived from neutrophil extracellular traps (NETs) and that LE patients develop pathogenic autoantibodies against these structures, including Abs to LL37. However, the mechanism that leads to the generation of these Abs is unknown. In this study, we show that NETs directly trigger Ab production by human memory B cells. This occurs via LL37-DNA complexes present in NETs, which have the unique ability to gain access to endosomal compartments of B cells and to trigger TLR9 activation. In LE patients, NET-derived LL37-DNA complexes trigger polyclonal B cell activation via TLR9, but also specifically expand self-reactive memory B cells producing anti-LL37 Abs in an Ag-dependent manner. These findings suggest a unique link between neutrophils and B cells in which NETs trigger a concerted activation of TLR9 and BCR leading to anti-NET autoantibody production in lupus.

Psoriasis is a T-cell-mediated skin autoimmune disease characterized by the aberrant activation of dermal dendritic cells (DCs) and the sustained epidermal expression of antimicrobial peptides. We have previously identified a link between these two events by showing that the cathelicidin antimicrobial peptide LL37 has the ability to trigger selfnucleic acid mediated activation of plasmacytoid DCs (pDCs) in psoriatic skin. Whether other cationic antimicrobial peptides exert similar activities is unknown. By analyzing heparin-binding HPLC fractions of psoriatic scales, we found that human beta-defensin (hBD)2, hBD3, and lysozyme are additional triggers of pDC activation in psoriatic skin lesions. Like LL37, hBD2, hBD3, and lysozyme are able to condense self-DNA into particles that are endocytosed by pDCs, leading to activation of TLR9. In contrast, other antimicrobial peptides expressed in psoriatic skin including elafin, hBD1, and psoriasin (S100A7) did not show similar activities. hBD2, hBD3, and lysozyme were detected in psoriatic skin lesions in the vicinity of pDCs and found to cooperate with LL37 to induce high levels of IFN production by pDCs, suggesting their concerted role in the pathogenesis of psoriasis.Keywords: Antimicrobial peptides r Plasmacytoid DC r Psoriasis r Skin r Toll-like receptor Additional supporting information may be found in the online version of this article at the publisher's web-site IntroductionPsoriasis is a common T-cell-mediated inflammatory disease of the skin, which, in its most prevalent form, is characterized by the appearance of scaly erythematous plaques that may cover large Correspondence: Dr. Michel Gilliet e-mail: Michel.gilliet@chuv.ch areas of the patient's body [1][2][3]. A key feature of psoriasis is the abnormal activation of dendritic cell (DC) subsets in the dermal compartment leading to the downstream T-cell-mediated autoimmune cascade [4]. A role for plasmacytoid DCs (pDCs) producing type I IFNs appears to be central in this process. pDC-derived * These authors contributed equally to this work.www.eji-journal.eu 204Roberto Lande et al. Eur. J. Immunol. 2015. 45: 203-213 IFNs activate conventional DCs that stimulate autoimmune T cells to migrate into the epidermis [5]. Here, these T cells produce Th17 cytokines 7], which directly initiate keratinocyte proliferation and an abnormal epidermal differentiation pattern [8,9]. Another key feature of psoriasis is the excessive production of antimicrobial peptides (AMPs) and proteins by keratinocytes [10][11][12]. These AMPs are best known for their role in killing pathogenic microorganisms such as Gram-positive and Gramnegative bacteria, protozoa, fungi, as well as some viruses [13]. The antimicrobial activity of AMPs has been ascribed to their unique cationic and amphiphatic structure, which allows interaction with and disruption of microbial membranes containing a high degree of negative charges. Three major antimicrobial peptide classes found in psoriatic skin are the cathelicidin, β-defensins, or S100 proteins. ...

Dendritic cell (DC) maturation is characterized by the gain or loss of immunological functions and by expression of distinctive surface receptors. CD38 is an ectoenzyme that catalyzes the synthesis of cyclic ADP ribose (a potent second messenger for Ca 2+ release), as well as a receptor that initiates transmembrane signaling upon engagement with its counterreceptor CD31 or with agonistic monoclonal antibodies. Since CD38 is expressed by resting monocytes, we aimed to monitor CD38 expression during the differentiation of human monocyte-derived DC (MDDC) and to investigate the possibility that CD38 plays a functional role during DC maturation. CD38 is down-modulated during differentiation into immature MDDC and expressed again upon maturation. The extent of CD38 expression is dependent on the stimulus adopted (LPS G IFN-+ G CD40 cross-linking). Although weak, IFN-+ consistently induces DC maturation. De novo-synthesized CD38 is enzymatically active, and its expression in mature (m) MDDC is dependent on NF-‹ B activity. However, CD38 is not merely a maturation marker but also mediates signaling in mMDDC, where it maintains its functions as a receptor. Activation via agonistic anti-CD38 mAb induces up-regulation of CD83 expression and IL-12 secretion, whereas disruption of CD38/CD31 interaction inhibits CD83 expression, IL-12 secretion and MDDC-induced allogeneic T cell proliferation.