IL-33, a new member of the IL-1 family cytokine, is involved in Th2-type responses in a wide range of diseases and signals through the ST2 receptor expressed on many immune cells. Since the effects of IL-33 on DCs remain controversial, we investigated the ability of IL-33 to modulate DC functions in vitro and in vivo. Here, we report that IL-33 activates myeloid DCs to produce IL-6, IL-1b, TNF, CCL17 and to express high levels of CD40, CD80 OX40L and CCR7. Importantly, IL-33-activated DCs prime naive lymphocytes to produce the Th2 cytokines IL-5 and IL-13, but not IL-4. In vivo, IL-33 exposure induces DC recruitment and activation in the lung. Using an OVA-induced allergic lung inflammation model, we demonstrate that the reduced airway inflammation in ST2-deficient mice correlates with the failure in DC activation and migration to the draining LN. Finally, we show that adoptive transfer of IL-33-activated DCs exacerbates lung inflammation in a DC-driven model of allergic airway inflammation. These data demonstrate for the first time that IL-33 activates DCs during antigen presentation and thereby drives a Th2-type response in allergic lung inflammation. IntroductionAllergic asthma is a chronic disorder characterized by eosinophilic airway inflammation, mucus hypersecretion, antigenspecific-IgE antibodies, airway remodeling and increased airway hyperreactivity [1,2]. The process of airway inflammation involves various cells types, such as eosinophils, mast cells, epithelial cells, lymphocytes and DCs. Th2 cells have been shown to play a predominant role in allergic asthma and Th2 cytokines, such as IL-4, IL-5 and IL-13, exacerbate disease severity [3,4]. IL-33, the recently discovered Th2 cytokine, is found at high levels in the plasma of asthmatic patients [5,6] and in the lungs of mice during experimental allergic asthma [7,8].IL-33 is a member of IL-1 family [9][10][11]. Like IL-1b or IL-18, IL-33 is synthesized as a precursor and can be cleaved by caspase-1 and 3 but the cleavage products are biologically less active than the precursor [12,13]. In contrast to the other IL-1 family members, IL-33 is mainly expressed in non-hematopoietic cells such as fibroblasts, epithelial cells and endothelial cells [10,14,15]. Because of its nuclear localization sequence, IL-33 is usually present in the nucleus, where it acts as a potential transcriptional repressor [16]. Recently, IL-33 has been shown to be released from necrotic cells and may act as an alarmin in a similar manner to IL-1a [17] or high mobility group box1 protein HMGB1 [18,19]. [14]. In accordance with its Th2 functions, administration of IL-33 into naive mice induces severe inflammation in the lung and digestive tract with elevated levels of IL-4, IL-5 and IL-13, splenomegaly and increased serum Ig [10]. In vitro, IL-33 has also been reported to polarize naive CD4 1 T cells to produce IL-5 and IL-13, but not . Polarization of this atypical Th2 population is independent of IL-4, STAT6 and GATA3. On macrophages, IL-33 amplifies IL-13-mediated polarization...

IL-22 is required for the onset of allergic asthma, but functions as a negative regulator of established allergic inflammation. Our study reveals that IL-22 contributes to the proinflammatory properties of IL-17A in experimental allergic asthma.

Lipoarabinomannans (LAM) and lipomannans (LM) are integral parts of the mycobacterial cell wall recognized by cells involved in the innate immune response and have been found to modulate the cytokine response. Typically, mannosylated LAM from pathogenic mycobacteria have been reported to be anti-inflammatory, whereas phosphoinositol-substituted LAM from nonpathogenic species are proinflammatory molecules. In this study, we show that LM from several mycobacterial species, including Mycobacterium chelonae, Mycobacterium kansasii, and Mycobacterium bovis bacillus Calmette-Guérin, display a dual function by stimulating or inhibiting proinflammatory cytokine synthesis through different pathways in murine primary macrophages. LM, but none of the corresponding LAM, induce macrophage activation characterized by cell surface expression of CD40 and CD86 and by TNF and NO secretion. This activation is dependent on the presence of Toll-like receptor (TLR) 2 and mediated through the adaptor protein myeloid differentiation factor 88 (MyD88), but independent of either TLR4 or TLR6 recognition. Surprisingly, LM exerted also a potent inhibitory effect on TNF, IL-12p40, and NO production by LPS-activated macrophages. This TLR2-, TLR6-, and MyD88-independent inhibitory effect is also mediated by LAM from M. bovis bacillus Calmette-Guérin but not by LAM derived from M. chelonae and M. kansasii. This study provides evidence that mycobacterial LM bear structural motifs susceptible to interact with different pattern recognition receptors with pro- or anti-inflammatory effects. Thus, the ultimate response of the host may therefore depend on the prevailing LM or LAM in the mycobacterial envelope and the local host cell receptor availability.

CD8+ T cells are a major defense against viral infections and intracellular parasites. Their production of interferon-gamma (IFN-gamma) and their cytolytic activity are key elements in the immune response to these pathogens. Mature mouse CD8+ T cells that were activated in the presence of interleukin-4 (IL-4) developed into a CD8-CD4- population that was not cytolytic and did not produce IFN-gamma. However, these CD8- cells produced large amounts of IL-4, IL-5, and IL-10 and helped activate resting B cells. Thus, CD8 effector functions are potentially diverse and could be exploited by infectious agents that switch off host protective cytolytic responses.

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NLRP3 inflammasome activation leading to IL-1 production is critical for the induction of a Th2 inflammatory allergic response.

SummaryVirus infections of the lung are thought to predispose individuals to asthma, a disease characterized by eosinophil infiltration of the airways. CD8 + T cells are an important part of the host response to virus infection, however, they have no reported role in eosinophil recruitment. We developed a mouse model of virus peptide-stimulated CD8 + T cell immune responses in the lung. We found that bystander CD4 + T helper cell type 2 immune responses to ovalbumin switched the virus peptide-specific CD8 + T cells in the lung to interleukin (IL) 5 production. Furthermore, when such IL-5-producing CD8 T cells were challenged via the airways with virus peptide, a significant eosinophil infiltration was induced. In vitro studies indicated that IL-4 could switch the virus-specific CD8 + T cells to IL-5 production. These results could explain the link between virus infection and acute exacerbation of asthma and, perhaps more importantly, they indicate an IL-4-dependent mechanism that would impair CD8 + T cell responses and delay viral clearance from the host.

The control of Listeria monocytogenes infection depends on the rapid activation of the innate immune system, likely through Toll-like receptors (TLR), since mice deficient for the common adapter protein of TLR signaling, myeloid differentiation factor 88 (MyD88), succumb to Listeria infection. In order to test whether TLR2 is involved in the control of infections, we compared the host response in TLR2-deficient mice with that in wild-type mice. Here we show that TLR2-deficient mice are more susceptible to systemic infection by Listeria than are wild-type mice, with a reduced survival rate, increased bacterial burden in the liver, and abundant and larger hepatic microabscesses containing increased numbers of neutrophils. The production of tumor necrosis factor, interleukin-12, and nitric oxide and the expression of the costimulatory molecules CD40 and CD86, which are necessary for the control of infection, were reduced in TLR2-deficient macrophages and dendritic cells stimulated by Listeria and were almost abolished in the absence of MyD88, coincident with the high susceptibility of MyD88-deficient mice to in vivo infection. Therefore, the present data demonstrate a role for TLR2 in the control of Listeria infection, but other MyD88-dependent signals may contribute to host resistance.