High mobility group box 1 (HMGB1) is an abundant and conserved nuclear protein that is released by necrotic cells and acts in the extracellular environment as a primary proinflammatory signal. In this study we show that human dendritic cells, which are specialized in Ag presentation to T cells, actively release their own HMGB1 into the extracellular milieu upon activation. This secreted HMGB1 is necessary for the up-regulation of CD80, CD83, and CD86 surface markers of human dendritic cells and for IL-12 production. The HMGB1 secreted by dendritic cells is also required for the clonal expansion, survival, and functional polarization of naive T cells. Using neutralizing Abs and receptor for advanced glycation end product-deficient (RAGE−/−) cells, we demonstrate that RAGE is required for the effect of HMGB1 on dendritic cells. HMGB1/RAGE interaction results in downstream activation of MAPKs and NF-κB. The use of an ancient signal of necrosis, HMGB1, by dendritic cells to sustain their own maturation and for activation of T lymphocytes represents a profitable evolutionary mechanism.

No abstract

Dendritic cells (DC) are key components of innate and adaptive immune responses. Plasmacytoid DC (PDC) are a specialized DC subset that produce high amounts of type I interferons in response to microbes. High mobility group box 1 protein (HMGB1) is an abundant nuclear protein, which acts as a potent pro-inflammatory factor when released extracellularly. We show that HMGB1 leaves the nucleus of maturing PDC following TLR9 activation, and that PDC express on the plasma membrane the bestcharacterized receptor for HMGB1, RAGE. Maturation and type I IFN secretion of PDC is hindered when the HMGB1/RAGE pathway is disrupted. These results reveal HMGB1 and RAGE as the first known autocrine loop modulating the maturation of PDC, and suggest that antagonists of HMGB1/RAGE might have therapeutic potential for the treatment of systemic human diseases. IntroductionDendritic cells (DC) are potent antigen-presenting cells bridging the innate and adaptive immune responses. To date, two subsets of DC have been identified in humans: myeloid DC and plasmacytoid DC (PDC), the latter also referred to as type I interferon (IFN-a)-producing cells [1][2][3][4][5][6]. PDC recognize viral or bacterial DNA patterns, consisting of unmethylated CpG motifs in the context of species-dependent surrounding sequences (CpG) [7]. As a consequence they produce, within a few hours, large amounts of . Based on their ability to induce IFN-a secretion by PDC, two types of CpG have been described: CpG 2216 (CpG-A), which induces high amounts of IFN-a, and CpG 2006 (CpG-B), which promotes survival, maturation and migration of PDC to the lymph nodes, but induces lower amounts of . PDC sustain the priming of naive T cells and their differentiation into Th1/Th2 effectors [15][16][17] or into regulatory T cells [16,[18][19][20][21][22].Recent studies shed light on the events involved in the recognition of microbial DNA by human PDC, the only subset of human DC that expresses the Toll-like receptor 9 (TLR9) [12]. Both CpG-A and CpG-B have been shown to activate PDC via TLR9 [23]. Upon phagocytosis PDC lyse microorganisms in phagolysosomes, where microbial DNA interacts with and activates TLR9 derived from the endoplasmic reticulum [24]. TLR9 activation leads to recruitment of the MyD88 adaptor protein and phosphorylation of the IL-1R-associated kinase (IRAK). Phosphorylated IRAK associates with the adaptor molecule TNF-associated factor 6 (TRAF6) [25]. Two separate signaling pathways, JNK and NF-jB, are then activated, promoting PDC maturation and survival. IFN-a induction, an event exclusively occurring in PDC, depends on the formation of a complex consisting of MyD88, TRAF6 and the IRF7 transcription factor, as well as on TRAF6-dependent ubiquitination [26].The events that determine the outcome of the interaction of PDC with T cells, and in particular the induction of effector or regulatory immune responses, are poorly characterized. Environmental signals that Here we report that HMGB1 is exported from the nucleus of PDC upon selective engagement of TLR9 an...

Pentraxins (PTX) and complement belong to the humoral arm of the innate immune system and have essential functions in immune defense to microbes and in scavenging cellular debris. The prototypic long PTX, PTX3, and the first component of the classical complement pathway, C1q, are innate opsonins involved in the disposal of dying cells by phagocytes. Whether the interaction between various innate opsonins impacts on their function is not fully understood. We show here that characterized Toll-like receptor (TLR) ligands elicit the production of C1q and PTX3 by immature dendritic cells (DC). Moreover, these molecules bind to dying cells with similar kinetics, although they recognize different domains on the cell membranes. PTX3 binds in the fluid phase to C1q, decreasing C1q deposition and subsequent complement activation on apoptotic cells. C1q increases the phagocytosis of apoptotic cells by DC and the release of interleukin-12 in the presence of TLR4 ligands and apoptotic cells; PTX3 inhibits both events. Moreover, PTX3 inhibited the cross-presentation of the MELAN-A/melanoma antigen-reactive T cell 1 (MART-1) tumor antigen expressed by dying cells, even in the presence of C1q. These results suggest that interaction of C1q and PTX3 influences the clearance of apoptotic cells by DC. The coordinated induction by primary, proinflammatory signals of C1q and PTX3 and their reciprocal regulation during inflammation influences the clearance of apoptotic cells by antigen-presenting cells and possibly plays a role in immune homeostasis.

Rationale:Patients with acute coronary syndrome (ACS) predisposed to recurrent coronary events have an expansion of a distinctive T-cell subset, the CD4 ؉ CD28 null T cells. These cells are highly inflammatory and cytotoxic in spite of lacking the costimulatory receptor CD28, which is crucial for optimal T cell function. The mechanisms that govern CD4 ؉ CD28null T cell function are unknown.Objective: Our aim was to investigate the expression and role of alternative costimulatory receptors in CD4 ؉ CD28 null T cells in ACS. Methods and Results: Expression of alternative costimulatory receptors (inducible costimulator, OX40, 4 -1BB,cytotoxic T lymphocyte associated antigen-4, programmed death-1) was quantified in CD4 ؉ CD28 null T cells from circulation of ACS and stable angina patients. Strikingly, in ACS, levels of OX40 and 4-1BB were significantly higher in circulating CD4 ؉ CD28null T cells compared to classical CD4 ؉ CD28 ؉ T lymphocytes. This was not observed in stable angina patients. Furthermore, CD4؉ CD28 null T cells constituted an important proportion of CD4 ؉ T lymphocytes in human atherosclerotic plaques and exhibited high levels of OX40 and 4-1BB. In addition, the ligands for OX40 and 4-1BB were present in plaques and also expressed on monocytes in circulation. Importantly, blockade of OX40 and 4-1BB reduced the ability of CD4 ؉ CD28null T cells to produce interferon-␥ and tumor necrosis factor-␣ and release perforin. Key Words: atherosclerosis Ⅲ coronary disease Ⅲ immune system Ⅲ lymphocytes Ⅲ receptors C oronary artery disease continues to be the leading cause of death in the developed world. Recent research has demonstrated that coronary artery disease results from an uncontrolled immune response and T lymphocytes have a central role in the development and progression of the disease. 1,2 Detailed analysis of CD4 ϩ T cells in coronary artery disease unveiled an increased frequency of a distinctive subset of lymphocytes called CD4 ϩ CD28 Conclusions: Costimulatory pathways are altered in CD4؉null T cells. 3 These cells are characterized by the lack of CD28, the main costimulatory receptor that regulates the response of T lymphocytes to antigen. 4 The CD4 ϩ CD28null T cell subset is present in low frequencies in healthy individuals and has also been shown to increase in patients with chronic inflammatory diseases such as autoimmunity. 5 In coronary artery disease, the frequency of CD4 The proinflammatory features of CD4 ϩ CD28 null T lymphocytes are surprising, as the activation and survival of T cells depends on costimulatory signals delivered via the CD28 receptor. 4 The activation of T cells requires not only the recognition of antigen, but also a second signal delivered by the interaction of the CD28 costimulatory receptor on T cells with its ligands on antigen presenting cells. 4 CD28 signaling controls the expression of interleukin-2 receptors and the production of interleukin-2 by activated T cells, which enable their proliferation, differentiation into effectors and survival. 12 Indeed, in th...