Monophosphoryl lipid A directly regulates Th1 cytokine production in human CD4+ T-cells through Toll-like receptor 2 and 4.

BACKGROUND: The monophosphoryl lipid A (MPLA) is a detoxified LPS derivative and an emerging safe immune adjuvant in human vaccine development. The adjuvant MPLA promotes antigen-presenting cell (APC) function and preferentially induces a Th1 response following vaccination. However, the mechanism by which the MPLA detoxicates and exerts its adjuvants effect on T-cell, particualrly the Th1 response is unknown. AIMS: We assessed the direct effects of MPLA on murine and human CD4+ T-cell proliferation and the profile of cytokine production ex vivo. RESULTS: We report that CD4+ T-cells only express functional TLR2 and TLR4 when activated by TCR stimulation, in particularly in the presence of IFNα. The activated T cells thereafter can respond directly to MPLA. MPLA does not affect T-cell proliferation in human T cells, but can induce a balanced Th1 cytokine profile in CD4+ T-cells by reducing the production of Th1 cytokines and enhancing the production of the regulatory cytokine IL-10. The MPLA-mediated regulatory effect on activated CD4+ T-cells is TLR2 and TLR4 dependent and can be abolished by the lipid A blocker polymyxin B. CONCLUSION: These data provide evidence, at least in part, for the safe induction of an appropriate level of Th1 response by adjuvant MPLA in human vaccine development.

Interleukin-33 promoting Th1 lymphocyte differentiation dependents on IL-12.

The pro-Th2 cytokine IL-33 is now emerging as an important Th1 cytokine-IFN-γ inducer in murine CD4(+) T cells that is essential for protective cell-mediated immunity against viral infection in mice. However, whether IL-33 can promote human Th1 cell differentiation and how IL-33 polarizes Th1 cells is less understood. We assessed the ability of IL-33 to induce Th1 cell differentiation and IFN-γ production in vitro and in vivo. We report here that IL-33 alone had no ability in Th1 cell polarization. However it potentiated IL-12-mediated Th1 cell differentiation and IFN-γ production in TCR-stimulated murine and human CD4(+) T cells in vitro and in vivo. IL-33 promoted Th1 cell development via MyD88 and synergized with IL-12 to enhance St2 and IL-12R expression in CD4(+) T cells. These data therefore provide a novel mechanism for Th1 cell differentiation and optimal induction of a Type 1 response. Thus, IL-33 is capable of inducing IL-12-dependent Th1 cell differentiation in human and mouse CD4(+) T cells.

IL-33 promotes ST2-dependent lung fibrosis by the induction of alternatively activated macrophages and innate lymphoid cells in mice.

BACKGROUND: The initiation and regulation of pulmonary fibrosis are not well understood. IL-33, an important cytokine for respiratory diseases, is overexpressed in the lungs of patients with idiopathic pulmonary fibrosis. OBJECTIVES: We aimed to determine the effects and mechanism of IL-33 on the development and severity of pulmonary fibrosis in murine bleomycin-induced fibrosis. METHODS: Lung fibrosis was induced by bleomycin in wild-type or Il33r (St2)(-/-) C57BL/6 mice treated with the recombinant mature form of IL-33 or anti-IL-33 antibody or transferred with type 2 innate lymphoid cells (ILC2s). The development and severity of fibrosis was evaluated based on lung histology, collagen levels, and lavage cytology. Cytokine and chemokine levels were quantified by using quantitative PCR, ELISA, and cytometry. RESULTS: IL-33 is constitutively expressed in lung epithelial cells but is induced in macrophages by bleomycin. Bleomycin enhanced the production of the mature but reduced full-length form of IL-33 in lung tissue. ST2 deficiency, anti-IL-33 antibody treatment, or alveolar macrophage depletion attenuated and exogenous IL-33 or adoptive transfer of ILC2s enhanced bleomycin-induced lung inflammation and fibrosis. These pathologic changes were accompanied, respectively, by reduced or increased IL-33, IL-13, TGF-ß1, and inflammatory chemokine production in the lung. Furthermore, IL-33 polarized M2 macrophages to produce IL-13 and TGF-ß1 and induced the expansion of ILC2s to produce IL-13 in vitro and in vivo. CONCLUSIONS: IL-33 is a novel profibrogenic cytokine that signals through ST2 to promote the initiation and progression of pulmonary fibrosis by recruiting and directing inflammatory cell function and enhancing profibrogenic cytokine production in an ST2- and macrophage-dependent manner.

Anti-Toll-like receptor 2 and 4 antibodies suppress inflammatory response in mice.

Toll-like receptors (TLRs) 2 and 4 recognize different endogenous and exogenous agonists and play a distinct role in infection and inflammation. However, their ultimate effect in a given infectious and inflammatory disease is less understood. We produced polyclonal anti-murine TLR2 and TLR4 antibodies and investigated their effect on cutaneous leishmaniasis and inflammatory arthritis. Administration of these antibodies to susceptible BALB/c mice, infected in the footpad with Leishmania major, reduced footpad swelling but not the parasite load compared with mice treated with control IgG. The antibodies synergistically reduced leishmanial-specific T-cell proliferation, T helper type 1 and type 2 cytokine production, specific IgG1 and IgG2a antibody synthesis, and T-cell receptor and co-stimulatory molecule expression on dendritic cells in infected mice. We then tested the effect of these antibodies on collagen-induced arthritis (CIA) in DBA/1 mice, a classic model of chronic inflammation. Both antibodies markedly suppressed the development of clinical parameters with concomitant reduction of pro-inflammatory cytokine production. These data therefore suggest that anti-TLR2 and 4 antibodies may have a synergistic therapeutic effect on inflammatory disease in vivo.

Interleukin-33 exacerbates acute colitis via interleukin-4 in mice.

Interleukin-33 (IL-33) and its receptor ST2 are over-expressed in clinical colitis tissue. However, the significance of these observations is at present unknown. Significantly, we demonstrate here that IL33 and ST2 are the primary early genes induced in the inflamed colon of BALB/c mice following dextran sulphate sodium (DSS)-induced experimental ulcerative colitis. Accordingly diarrhoea and DSS-induced colon inflammation were impaired in ST2(-/-) BALB/c mice and exacerbated in wild-type mice by treatment with exogenous recombinant IL-33, associated respectively with reduced and enhanced expression of chemokines (CXCL9 and CXCL10), and inflammatory (IL-4, IL-13, IL-1, IL-6, IL-17) and angiogenic (vascular endothelial growth factor) cytokines in vivo. The exacerbation effect of treatment with recombinant IL-33 on DSS-induced acute colitis was abolished in IL-4(-/-) BALB/c mice. Hence, IL-33 signalling via ST2, by inducing an IL-4-dependent immune response, may be a major pathogenic factor in the exacerbation of ulcerative colitis.

Resveratrol modulates murine collagen-induced arthritis by inhibiting Th17 and B-cell function.

BACKGROUND: Alcohol intake is inversely related to rheumatoid arthritis (RA) disease incidence and severity. Resveratrol, a safe, well-described plant-derived compound, possesses anti-inflammation and immune-regulatory properties and is present in red wine. As such, it could mediate anti-inflammatory properties of the latter and offer novel therapeutic utility in is own right. OBJECTIVE: To evaluate the therapeutic effect of resveratrol on collagen-induced arthritis (CIA) and its putative immune modulation in mice. METHODS: CIA was induced in DBA1 mice by immunisation with collagen II. Different doses of resveratrol were administered before or after the development of CIA. The levels of antibody and cytokines in serum or in draining lymph node (DLN) lymphocyte culture supernatants were measured by ELISA and Th17 cell development in DLN was monitored by flow cytometry. RESULTS: Either prophylactic or therapeutic administration of resveratrol attenuated clinical parameters and bone erosion in CIA mice. The arthritis-protective effects were associated with markedly reduced serum levels of pro-inflammatory cytokines and collagen-specific, but not total, IgG, and with reduced numbers of Th17 cells and the production of IL-17 in DLN. CONCLUSION: Resveratrol modulates inflammatory arthritis in rodents by selectively suppressing key cellular and humoral responses necessary for disease development. This may partly explain the protective effects of red wine but importantly may offer a novel, effective and safe pathway whereby novel agents could be developed to treat RA.

IL-33 activates B1 cells and exacerbates contact sensitivity.

B1 B cells produce natural IgM and play a critical role in the early defense against bacterial and viral infection. The polyreactive IgM also contributes to the clearance of apoptotic products and plays an important role in autoimmune pathogenesis. However, the mechanism of activation and proliferation of B1 cells remains obscure. In this study, we report that IL-33, a new member of IL-1 family, activates B1 cells, which express the IL-33 receptor α, ST2. IL-33 markedly activated B1 cell proliferation and enhanced IgM, IL-5, and IL-13 production in vitro and in vivo in a ST2-dependent manner. The IL-33-activated B1 cell functions could be largely abolished by IL-5 neutralization and partially reduced by T cell or mast cell deficiency in vivo. ST2-deficient mice developed less severe oxazolone-induced contact sensitivity (CS) than did wild-type (WT) mice. Furthermore, IL-33 treatment significantly exacerbated CS in WT mice with enhanced B1 cell proliferation and IgM and IL-5 production. Moreover, IL-33-activated B1 cells from WT mice could adoptively transfer enhanced CS in ST2(-/-) mice challenged with IL-33. Thus, we demonstrate, to the best of our knowledge, a hitherto unrecognized mechanism of B1 cell activation and IL-33 function, and suggest that IL-33 may play an important role in delayed-type hypersensitivity.

Direct recognition of LPS by human but not murine CD8+ T cells via TLR4 complex.

LPS comprises a major PAMP and is a key target of the immune system during bacterial infection. While LPS can be recognised by innate immune cells via the TLR4 complex, it is unknown whether T lymphocytes, especially CD8(+) T cells are also capable of doing so. We report here that naive human CD8(+) T cells, after activation by TCR stimulation, express surface TLR4 and CD14. These activated CD8(+) T cells can then secrete high concentrations of IFN-gamma, granzyme and perforin in response to LPS. These effects can be specifically inhibited using siRNA for TLR4. Furthermore, LPS can synergize with IL-12 to polarize the CD8(+) T cells into cytotoxic T-cell 1 (Tc1) that produce IFN-gamma but not IL-4, with or without TCR activation. Moreover, CD8(+)CD45RO(+) memory T cells constitutively expressed TLR4 and markedly enhanced IFN-gamma production when stimulated with LPS. In contrast, activated murine CD8(+) T cells lack TLR4 and CD14 expression and fail to respond to LPS for proliferation and cytokine production. Thus, human but not murine CD8(+) T cells are able to directly recognise bacterial LPS via LPS receptor complex and TLR4 provides a novel signal for the activation of effector and memory human CD8(+) T cells.

IL-33 induces antigen-specific IL-5+ T cells and promotes allergic-induced airway inflammation independent of IL-4.

Type 2 cytokines (IL-4, IL-5, and IL-13) play a pivotal role in helminthic infection and allergic disorders. CD4(+) T cells which produce type 2 cytokines can be generated via IL-4-dependent and -independent pathways. Although the IL-4-dependent pathway is well documented, factors that drive IL-4-independent Th2 cell differentiation remain obscure. We report here that the new cytokine IL-33, in the presence of Ag, polarizes murine and human naive CD4(+) T cells into a population of T cells which produce mainly IL-5 but not IL-4. This polarization requires IL-1R-related molecule and MyD88 but not IL-4 or STAT6. The IL-33-induced T cell differentiation is also dependent on the phosphorylation of MAPKs and NF-kappaB but not the induction of GATA3 or T-bet. In vivo, ST2(-/-) mice developed attenuated airway inflammation and IL-5 production in a murine model of asthma. Conversely, IL-33 administration induced the IL-5-producing T cells and exacerbated allergen-induced airway inflammation in wild-type as well as IL-4(-/-) mice. Finally, adoptive transfer of IL-33-polarized IL-5(+)IL-4(-)T cells triggered airway inflammation in naive IL-4(-/-) mice. Thus, we demonstrate here that, in the presence of Ag, IL-33 induces IL-5-producing T cells and promotes airway inflammation independent of IL-4.

Galectin-3 is a negative regulator of lipopolysaccharide-mediated inflammation.

Galectin-3 is a beta-galactoside-binding lectin that plays an important role in inflammatory diseases. It also interacts with the surface carbohydrates of many pathogens, including LPS. However, its role in infection is not fully understood. Data presented herein demonstrate for the first time that galectin-3 is a negative regulator of LPS-induced inflammation. Galectin-3 is constitutively produced by macrophages and directly binds to LPS. Galectin-3-deficient macrophages had markedly elevated LPS-induced signaling and inflammatory cytokine production compared with wild-type cells, which was specifically inhibited by the addition of recombinant galectin-3 protein. In contrast, blocking galectin-3 binding sites by using a neutralizing Ab or its ligand, beta-lactose, enhanced LPS-induced inflammatory cytokine expression by wild-type macrophages. In vivo, mice lacking galectin-3 were more susceptible to LPS shock associated with excessive induction of inflammatory cytokines and NO production. However, these changes conferred greater resistance to Salmonella infection. Thus, galectin-3 is a previously unrecognized, naturally occurring, negative regulator of LPS function, which protects the host from endotoxin shock but, conversely, favors Salmonella survival.

IL-33 is a chemoattractant for human Th2 cells.

IL-33 is a novel cytokine of the IL-1 family and mediates its biological effect via the receptor ST2, which is selectively expressed on Th2 cells but not Th1 cells. IL-33 drives production of Th2-associated cytokines including IL-5 and IL-13 and thereby promotes defense and pathology in mucosal organs. Cell locomotion is crucial to the induction of an effective immune response. We report here the chemoattraction of Th2 cells by IL-33. Recombinant IL-33 increased the proportion of human Th2 cells, but not Th1 cells, in polarized morphology in vitro and stimulated their subsequent invasion into collagen gels in an IL-33 concentration-dependent manner. Injection of recombinant IL-33 into the footpad of ST2(-/-) mice which had been adoptively transferred with polarized Th2 cells, led to local accumulation of the transferred Th2 cells. These data therefore demonstrate that IL-33 is a selective Th2 chemoattractant associated with the pro-inflammatory property of this novel cytokine.

Toll-like receptor 2 signaling modulates the functions of CD4+ CD25+ regulatory T cells.

Toll-like receptors (TLRs) are primary sensors of both innate and adaptive immune systems and play a pivotal role in response against structurally conserved components of pathogens. Synthetic bacterial lipoprotein (BLP) Pam3Cys-SK4 is a TLR2 agonist that is capable of modulating T cell immune responses. We show here that BLP, together with anti-CD3 antibody [T cell receptor (TcR) activation], induced proliferation of both CD4+ CD25+ regulatory T cells (Tregs) and CD4+ CD25- (effector) T cells in the absence of antigen-presenting cells. The expanded Tregs showed a transient loss of suppressive activity. Moreover, BLP rendered effectors resistant to the suppression of Tregs by increasing IL-2 secretion. BLP also transiently suppressed the induction of Foxp3 (X-linked forkhead/winged helix transcription factor) mRNA in Tregs at the first 8-15 h after T cell receptor activation. Consistent with this observation, BLP-stimulated Tregs regained their inhibitory activity and prevented spontaneous colitis induced by effectors in severe combined immunodeficient mice. Our results demonstrate a previously unrecognized pathway by which TLR expressed on T cells may directly modulate the immune response. Thus, during an acute bacterial infection, BLP may rapidly increase the host's adaptive immunity by expanding effectors and also by attenuating the suppressive activity of Tregs. In the process, BLP also expands the Tregs, which recover their suppressive activity when the infection has subsided, in time to limit potential autoimmunity that might result from the overactivated effectors.

Expression and function of Toll-like receptor on T cells.

Toll is the founder of a group of pattern recognition receptors, which play a critical role in the innate immunity in Drosophila. At least 13 distinct Toll-like receptors (TLRs), recognising pathogen-associated molecular pattern (PAMPs), have now been identified in humans. Most investigations on TLRs have focused on cells of the innate system. We report here that naïve human T cells expressed high levels of cell surface TLR2 after activation by anti-T cell receptor (TCR) antibody and interferon-alpha. Activated cells produced elevated levels of cytokines in response to the TLR2 ligand, bacterial lipopeptide (BLP). Furthermore, CD4(+)CD45RO(+) memory T cells from peripheral blood constitutively expressed TLR2 and produced IFNgamma in response to BLP. BLP also markedly enhanced the proliferation and IFNgamma production by CD45RO(+) T cells in the presence of IL-2 or IL-15. Thus, TLR2 serves as a co-stimulatory receptor for antigen-specific T cell development and participates in the maintenance of T cell memory. This suggests that pathogens, via their PAMPs, may contribute directly to the perpetuation and activation of long term T cell memory in both antigen dependent and independent manner.

TLR2 is expressed on activated T cells as a costimulatory receptor.

Toll is the founder of a group of pattern recognition receptors that play a critical role in the innate immunity in Drosophila. At least 10 distinct Toll-like receptors (TLRs), recognizing pathogen-associated molecular patterns, have now been identified in humans. Most investigations on TLRs have focused on cells of the innate system. We report here that naïve human T cells expressed high levels of cell-surface TLR2 after activation by anti-T cell receptor antibody and IFN-alpha. Activated cells produced elevated levels of cytokines in response to the TLR2 ligand, bacterial lipopeptide. Furthermore, CD4(+)CD45RO(+) memory T cells from peripheral blood constitutively expressed TLR2 and produced IFN-gamma in response to bacterial lipopeptide, which also markedly enhanced the proliferation and IFN-gamma production by CD45RO(+) T cells in the presence of IL-2 or IL-15. Thus, TLR2 serves as a costimulatory receptor for antigen-specific T cell development and participates in the maintenance of T cell memory. This suggests that pathogens, via their pathogen-associated molecular patterns, may contribute directly to the perpetuation and activation of long-term T cell memory in both antigen-dependent and independent manner.

Direct and indirect role of Toll-like receptors in T cell mediated immunity.

Toll-like receptors (TLRs) are pathogen-associated molecular patterns (PAMPs) recognition receptors that play an important role in protective immunity against infection and inflammation. They act as central integrators of a wide variety of signals, responding to diverse agonists of microbial products. Stimulation of Toll-like receptors by microbial products leads to signaling pathways that activate not only innate, but also adaptive immunity by APC dependent or independent mechanisms. Recent evidence revealed that TLR signals played a determining role in the skewing of naive T cells towards either Th1 or Th2 responses. Activation of Toll-like receptors also directly or indirectly influences regulatory T cell functions. Therefore, TLRs are required in both immune activation and immune regulation. Study of TLRs has significantly enhanced our understanding of innate and adaptive immune responses and provides novel therapeutic approaches against infectious and inflammatory diseases.

Chemoattraction of human T cells by IL-18.

Cell locomotion is crucial to the induction of an effective immune response. We report here the chemoattraction of CD4(+) T cells by IL-18, a member of the IL-1 cytokine family. Recombinant IL-18 increased the proportion of T cells in polarized morphology in vitro and stimulated their subsequent invasion into collagen gels in an IL-18 concentration gradient-dependent manner. Immunofluorescent microscopy studies determined that the major cell type responding to IL-18 was IL-18R(+)CD4(+). Importantly, synovial CD4(+) T cells from patients with rheumatoid arthritis responded to IL-18, adopting polarized morphology and gel invasion without further activation ex vivo, indicating the physiologic relevance of our observations. Finally, injection of rIL-18 into the footpad of DBA/1 mice led to local accumulation of inflammatory cells. These data therefore demonstrate for the first time lymphocyte chemoattractant properties of a member of the IL-1 cytokine family and its relevance in inflammatory diseases.

CD4+CD25+ regulatory T cells suppress differentiation and functions of Th1 and Th2 cells, Leishmania major infection, and colitis in mice.

Regulatory T cells play a major role in modulating the immune response. However, most information on these cells centers on autoimmunity, and there is also considerable controversy on the functional characteristics of these cells. Here we provide direct in vitro and in vivo evidence that CD4+CD25+ regulatory T cells inhibit the differentiation and functions of both Th1 and Th2 cells. Importantly, CD4+CD25+ T cells suppressed the disease development of Leishmania major infection in SCID mice reconstituted with naive CD4+CD25- T cells. Furthermore, CD4+CD25+ T cells inhibited the development of colitis induced by both Th1 and Th2 cells in SCID mice. Our results therefore document that CD4+CD25+ regulatory T cells suppress both Th1 and Th2 cells and that these regulatory T cells have a profound therapeutic potential against diseases induced by both Th1 and Th2 cells in vivo.

Nitric oxide preferentially induces type 1 T cell differentiation by selectively up-regulating IL-12 receptor beta 2 expression via cGMP.

Nitric oxide plays an important role in immune regulation. We have shown that although high concentrations of NO generally were immune-suppressive, low concentrations of NO selectively enhanced the differentiation of T helper (Th)1 cells but not Th2 cells. This finding provided an explanation for the crucial role of NO in defense against intracellular pathogens. However, the mechanism for the selective induction of Th1 cells was unknown. We report here that at low concentrations, NO activates soluble guanylyl cyclase, leading to the up-regulation of cGMP, which selectively induces the expression of IL-12 receptor beta2 but has no effect on IL-4 receptor. Because IL-12 and IL-4 are the key cytokines for induction of Th1 and Th2 cells, respectively, these results, therefore, provide the mechanism for the selective action of NO on T cell subset differentiation. Furthermore, this selectivity also applies to CD8+ cytotoxic and human T cells and, thus, demonstrates the general implication of this observation in immune regulation. Our results also provide an example of the regulation of cytokine receptor expression by NO. The selectivity of such action via cGMP suggests that it is amenable to therapeutic intervention.