How are T(H)2-type immune responses initiated and amplified?

STAT6 and lung inflammation

Lung inflammation has many etiologies, including diseases of Th2-type immunity, such as asthma and anti-parasitic responses. Inflammatory diseases of the lung involve complex interactions among structural cells (airway epithelium, smooth muscle, and fibroblasts) and immune cells (B and T cells, macrophages, dendritic cells, and innate lymphoid cells). Signal transducer and activator of transcription 6 (STAT6) has been demonstrated to regulate many pathologic features of lung inflammatory responses in animal models including airway eosinophilia, epithelial mucus production, smooth muscle changes, Th2 cell differentiation, and IgE production from B cells. Cytokines IL-4 and IL-13 that are upstream of STAT6 are found elevated in human asthma and clinical trials are underway to therapeutically target the IL-4/IL-13/STAT6 pathway. Additionally, recent work suggests that STAT6 may also regulate lung anti-viral responses and contribute to pulmonary fibrosis. This review will focus on the role of STAT6 in lung diseases and mechanisms by which STAT6 controls immune and structural lung cell function.

Doxycycline suppresses Chlamydia pneumoniae-mediated increases in ongoing immunoglobulin E and interleukin-4 responses by peripheral blood mononuclear cells of patients with allergic asthma

OBJECTIVES

Chlamydia pneumoniae, an obligate intracellular bacterium, has been associated with asthma and the induction of immunoglobulin E (IgE) responses. Whereas tetracyclines have anti-chlamydial activity, their effect on human IgE responses to C. pneumoniae has not been studied.

METHODS

Peripheral blood mononuclear cells (PBMCs) from serum IgE+ allergic asthmatic subjects (n = 11) and healthy controls (n = 12) were infected with C. pneumoniae and cultured for 12 days with or without doxycycline (0.01-1.0 mg/L). IgE, interferon (IFN)-γ and interleukin (IL)-4 levels in supernatants were determined on days 1-12 post-infection, and C. pneumoniae DNA copy numbers in PBMC culture were measured on day 2 (quantitative PCR).

RESULTS

C. pneumoniae-infected PBMCs from allergic asthmatic individuals had increased levels of IgE in supernatants compared with uninfected PBMCs (520% on day 10 post-infection, P = 0.008). IgE levels in PBMC cultures from controls were undetectable (<0.3 ng/mL). Increases in C. pneumoniae-induced IgE in asthmatics correlated with those of C. pneumoniae-induced IL-4 (r = 0.98; P < 0.001), but not with IFN-γ. The addition of doxycycline (1.0 mg/L) to the culture strongly suppressed the production of IgE (>70%, P = 0.04) and IL-4 (75%, P = 0.018), but not IFN-γ. The suppressive effect on IL-4 production remained significant even at concentrations of doxycycline that were subinhibitory (0.01 mg/L) for C. pneumoniae. In both asthmatic participants and controls, no significant effect of doxycycline on DNA copy numbers of C. pneumoniae was observed.

CONCLUSIONS

Doxycycline suppressed the C. pneumoniae-induced production of IgE and IL-4, but not IFN-γ, in PBMCs from IgE+ allergic asthmatic subjects. These findings resulted from the immunomodulatory anti-allergic properties of tetracyclines.

Dendritic cells in myelodysplastic syndromes: from pathogenesis to immunotherapy

Myelodysplastic syndromes (MDS) are clonal disorders of the hematopoietic stem cell characterized by ineffective hematopoiesis leading to peripheral cytopenias. Different processes are involved in its pathogenesis, such as (epi)genetic alterations and immunological dysfunctions. The nature of immune dysregulation is markedly different between various MDS risk groups. In low-risk MDS, the immune system is in a proinflammatory state, whereas in high-risk disease, immunosuppressive features facilitate expansion of the dysplastic clone and can eventually lead to disease progression to acute myeloid leukemia. Various cell types contribute to dysregulation of immune responses in MDS. Dendritic cells (DCs) are important regulators of immunity. However, the role of DCs in MDS has yet to be elucidated. It has been suggested that impaired DC function can hamper adequate immune responses. This review focuses on the involvement of DCs in immune dysregulation in low- and high-risk MDS and the implications for DC-targeted therapies.

Activation of basophils by the double-stranded RNA poly(A:U) exacerbates allergic inflammation

BACKGROUND

It is commonly acknowledged that asthma is exacerbated by viral infections. On the other hand, basophil infiltration of lung tissues has been evidenced postmortem in cases of fatal disease, raising the question of a possible link between these two observations.

OBJECTIVES

Herein, we addressed the relationship between asthma exacerbation by viral infection and basophil activation and expansion by investigating how stimulation with the dsRNA polyadenylic/polyuridylic acid [poly(A:U)] affected basophil activities and recruitment in an allergic airway inflammation model.

METHODS

The effect of dsRNA on basophils was assessed by measuring the cytokine levels produced upon stimulation. We used an OVA-induced experimental model of allergic asthma. Airway hyperreactivity, recruitment of infiltrating cells, and cytokine production were determined in the lung of mice having received poly(A:U), as compared with untreated controls. The exacerbating effect of basophils was assessed both by adoptive transfer of poly(A:U)-treated basophils and by their in vivo depletion with Ba103 antibody.

RESULTS

We found that in vitro treatment with poly(A:U) increased basophil functions by inducing TH 2-type cytokine and histamine production, whereas in vivo treatment increased peripheral basophil recruitment. Furthermore, we provide the first demonstration for increased infiltration of basophils in the lung of mice suffering from airway inflammation. In this model, disease symptoms were clearly exacerbated upon adoptive transfer of basophils exposed to poly(A:U), relative to their unstimulated counterpart. Conversely, in vivo basophil depletion alleviated disease syndromes, thus validating the transfer data.

CONCLUSIONS

Our findings provide the first evidence for airway inflammation exacerbation by basophils following dsRNA stimulation.

Cytokine targets in airway inflammation

Asthma is an inflammatory disease of the airway wall that leads to bronchial hyper-reactivity and airway obstruction, caused by inflammation, mucus hyper-production and airway wall remodelling. Central to pathogenesis, Th2 and Th17 lymphocytes of the adaptive immune system control many aspects of the disease by producing cytokines such as IL-4, IL-5, IL-13, and IL-17. In addition, many cells of the innate immune system such as mast cells, basophils, neutrophils, eosinophils, dendritic cells (DCs), and innate lymphoid cells (ILCs) play an important role in the initiation or maintenance of disease. Epithelial cells are ever more implicated in disease pathogenesis, as they are able to sense exposure to pathogens via pattern recognition receptors (PRRs) and can activate DCs. This review article will deal with the role of cytokines that are considered essential controllers of the inflammatory, immune and regenerative response to allergens, viruses and environmental pollutants. Emerging Th2 cytokines such as thymic stromal lymphopoietin, GM-CSF, IL-1, IL-33, IL-25 mediate the crosstalk between epithelial cells, DCs, and ILCs. Understanding the crosstalk between structural cells, innate and adaptive immune cells that is mediated by cytokines provides important mechanistic insights into how asthma develops and perpetuates itself. It could also provide the framework on which we will select new therapeutic strategies that prevent exacerbations and alter the natural course of the disease.

IL-33-dependent induction of allergic lung inflammation by FcγRIII signaling

Atopic asthma is a chronic inflammatory disease of the lungs generally marked by excessive Th2 inflammation. The role of allergen-specific IgG in asthma is still controversial; however, a receptor of IgG-immune complexes (IgG-ICs), FcγRIII, has been shown to promote Th2 responses through an unknown mechanism. Herein, we demonstrate that allergen-specific IgG-ICs, formed upon reexposure to allergen, promoted Th2 responses in two different models of IC-mediated inflammation that were independent of a preformed T cell memory response. Development of Th2-type airway inflammation was shown to be both FcγRIII and TLR4 dependent, and T cells were necessary and sufficient for this process to occur, even in the absence of type 2 innate lymphoid cells. We sought to identify downstream targets of FcγRIII signaling that could contribute to this process and demonstrated that bone marrow-derived DCs, alveolar macrophages, and respiratory DCs significantly upregulated IL-33 when activated through FcγRIII and TLR4. Importantly, IC-induced Th2 inflammation was dependent on the ST2/IL-33 pathway. Our results suggest that allergen-specific IgG can enhance secondary responses by ligating FcγRIII on antigen-presenting cells to augment development of Th2-mediated responses in the lungs via an IL-33-dependent mechanism.

Protective and pathological roles of mast cells and basophils

Mast cells and basophils are potent effector cells of the innate immune system, and they have both beneficial and detrimental functions for the host. They are mainly implicated in pro-inflammatory responses to allergens but can also contribute to protection against pathogens. Although both cell types were identified more than 130 years ago by Paul Ehrlich, their in vivo functions remain poorly understood. The precursor cell populations that give rise to mast cells and basophils have recently been characterized and isolated. Furthermore, new genetically modified mouse strains have been developed, which enable more specific targeting of mast cells and basophils. Such advances offer new opportunities to uncover the true in vivo activities of these cells and to revisit their previously proposed effector functions.

Interleukin-2 at the crossroads of effector responses, tolerance, and immunotherapy

Interleukin-2 (IL-2) is a pleiotropic cytokine produced after antigen activation that plays pivotal roles in the immune response. Discovered as a T cell growth factor, IL-2 additionally promotes CD8(+) T cell and natural killer cell cytolytic activity and modulates T cell differentiation programs in response to antigen, promoting naïve CD4(+) T cell differentiation into T helper 1 (Th1) and T helper 2 (Th2) cells while inhibiting T helper 17 (Th17) and T follicular helper (Tfh) cell differentiation. Moreover, IL-2 is essential for the development and maintenance of T regulatory cells and for activation-induced cell death, thereby mediating tolerance and limiting inappropriate immune reactions. In this review, we focus on the molecular mechanisms and complex cellular actions of IL-2, its cooperative and opposing effects with other cytokines, and how both promoting and blocking the actions of IL-2 are being utilized in clinical medicine.

Inflammatory monocytes recruited to allergic skin acquire an anti-inflammatory M2 phenotype via basophil-derived interleukin-4

Monocytes and macrophages are important effectors and regulators of inflammation, and both can be divided into distinct subsets based on their phenotypes. The developmental and functional relationship between individual subsets of monocytes and those of macrophages has not been fully elucidated, although Ly6C(+)CCR2(+) inflammatory and Ly6C(-)CCR2(-) resident monocytes are generally thought to differentiate into M1 (classically activated) and M2 (alternatively activated) macrophages, respectively. Here we show that inflammatory monocytes recruited to allergic skin acquired an M2-like phenotype in response to basophil-derived interleukin-4 (IL-4) and exerted an anti-inflammatory function. CCR2-deficient mice unexpectedly displayed an exacerbation rather than alleviation of allergic inflammation, in spite of impaired recruitment of inflammatory monocytes to skin lesions. Adoptive transfer of inflammatory monocytes from wild-type but not IL-4 receptor-deficient mice dampened the exacerbated inflammation in CCR2-deficient mice. Thus, inflammatory monocytes can be converted from being proinflammatory to anti-inflammatory under the influence of basophils in allergic reactions.

An efferocytosis-induced, IL-4-dependent macrophage-iNKT cell circuit suppresses sterile inflammation and is defective in murine CGD

Efferocytosis of apoptotic neutrophils by macrophages following tissue injury is fundamental to the resolution of inflammation and initiation of tissue repair. Using a sterile peritonitis model in mice, we identified interleukin (IL)-4-producing efferocytosing macrophages in the peritoneum that activate invariant natural killer T (iNKT) cells to produce cytokines including IL-4, IL-13, and interferon-γ. Importantly, IL-4 from macrophages contributes to alternative activation of peritoneal exudate macrophages and augments type 2 cytokine production from NKT cells to suppress inflammation. The increased peritonitis in mice deficient in IL-4, NKT cells, or IL-4Rα expression on myeloid cells suggested that each is a key component for resolution of sterile inflammation. The reduced NAD phosphate oxidase is also critical for this model, because in mice with X-linked chronic granulomatous disease (X-CGD) that lack oxidase subunits, activation of iNKT cells by X-CGD peritoneal exudate macrophages was impaired during sterile peritonitis, resulting in enhanced and prolonged inflammation in these mice. Therefore, efferocytosis-induced IL-4 production and activation of IL-4-producing iNKT cells by macrophages are immunomodulatory events in an innate immune circuit required to resolve sterile inflammation and promote tissue repair.

TSLP promotes induction of Th2 differentiation but is not necessary during established allergen-induced pulmonary disease

Thymic stromal lymphopoietin (TSLP) has been implicated in the development of allergic inflammation by promoting Th2-type responses and has become a potential therapeutic target. Using in vitro T cell differentiation cultures we were able to validate that TSLP played a more critical role in the early development of Th2 immune responses with less significant enhancement of already developed Th2 responses. Adoptive transfer of naive DO11.10 ovalbumin-specific T cells followed by airway exposure to ovalbumin showed an early impairment of Th2 immune response in TSLP−/− mice compared to wild type mice during the development of a Th2 response. In contrast, transfer of already differentiated Th2 cells into TSLP−/− mice did not change lung pathology or Th2 cytokine production upon ovalbumin challenge compared to transfer into wild type mice. An allergen-induced Th2 airway model demonstrated that there was only a difference in gob5 expression (a mucus-associated gene) between wild type and TSLP−/− mice. Furthermore, when allergic animals with established disease were treated with a neutralizing anti-TSLP antibody there was no change in airway hyperreponsiveness (AHR) or Th2 cytokine production compared to the control antibody treated animals, whereas a change in gob5 gene expression was also observed similar to the TSLP−/− mouse studies. In contrast, when animals were treated with anti-TSLP during the initial stages of allergen sensitization there was a significant change in Th2 cytokines during the final allergen challenge. Collectively, these studies suggest that in mice TSLP has an important role during the early development of Th2 immune responses, whereas its role at later stages of allergic disease may not be as critical for maintaining the Th2-driven allergic disease.

Adjuvant selection for vaccination against murine schistosomiasis

Schistosoma mansoni cercariae penetrate mouse epidermis, detach the glycocalyx and transform into schistosomula, triggering innate immune responses by host keratinocytes and Langerhans cells. Schistosomula leave the dermis and enter blood capillaries, releasing excretory/secretory products (ESP), which induce readily detectable primary adaptive immunity responses, dominated by T helper (Th) 1 and 17 cytokines. Partial protection against murine schistosomiasis may be achieved using subunit antigens and Th1 cytokine-inducing adjuvants. Conversely, resistance to primary and/or secondary schistosomiasis in rats, mice and humans is associated with production of Th2 cytokines. Accordingly, we reasoned that effective vaccination against murine primary schistosomiasis might be achieved provided selection of an adjuvant capable of skewing the S. mansoni larval ESP-mediated Th1/Th17 immune responses towards a Th2 profile. In an aim to select such an adjuvant, we administered the prototypical Th1 and Th2, respectively, C57BL/6 and BALB/c mice with polyinosinic-polycytidylic acid (Poly I/C), peptidoglycan (PGN), or thymic stromal lymphopoietin (TSLP) before exposure to S. mansoni cercariae. Serum antibody reactivity and ex vivo spleen cells (SC) immune responses to larval ESP, in a recombinant or multiple antigen peptide form, were assessed 1 week after infection. Injection with Poly I/C failed to increase interleukin (IL)-4 and led to elevated gamma interferon (IFN-γ) levels released by unstimulated or ESP-stimulated SC. Treatment with PGN triggered hightened amounts of IL-4, IL-17 and IFN-γ released by unstimulated or ESP-stimulated C57BL/6 SC. In contrast, TSLP succeeded in directing the ESP-mediated immune responses towards a Th2-biased profile in prototypical Th1 and Th2 mice.

Toll-like receptor activation in basophils contributes to the development of IgG4-related disease

BACKGROUND

IgG4-related disease (IRD) is characterized by systemic IgG4 antibody responses and by infiltration of IgG4-expressing plasma cells into the affected organs. Although T helper type 2 (Th2) cytokines are implicated in enhanced IgG4 responses, molecular mechanisms accounting for the development of IgG4 antibody responses are poorly defined. Since basophils function as antigen-presenting cells for Th2 responses, we tried to clarify the role of basophils in the development of IgG4 responses in this study.

METHODS

IgG4 and cytokine responses to various nucleotide-binding oligomerization domain-like receptor and Toll-like receptor (TLR) ligands were examined by using basophils isolated from healthy controls and from patients with IgG4-related disease.

RESULTS

Activation of TLRs in basophils from healthy controls induced IgG4 production by B cells, which effect was associated with enhanced production of B cell activating factor (BAFF) and IL-13. In addition, activation of TLRs in basophils from patients with IRD induced a large amount of IgG4 by B cells from healthy controls. This enhancement of IgG4 production was again associated with BAFF and IL-13.

CONCLUSIONS

These data suggest that innate immune responses mediated through TLRs may play a role in the development of IgG4-related disease, in part by production of BAFF from basophils.

Functional analysis of the impact of ORMDL3 expression on inflammation and activation of the unfolded protein response in human airway epithelial cells

Background

The gene ORMDL3 was shown to be associated with early-onset asthma susceptibility in multiple independent genome-wide and candidate-gene association studies. Asthmatic patients have elevated expression levels of this gene. ORMDL3 encodes a transmembrane protein localized in the endoplasmic reticulum (ER) that may be involved in ER stress and inflammation. It is essential to validate the genetic associations linking ORMDL3 with asthma through functional studies that confirm the biological relevance of this gene in disease. We investigated the effects of manipulating ORMDL3 expression levels in vitro in airway cells on innate immune inflammatory responses, ER stress and activation of the unfolded protein response (UPR).

Methods

ORMDL3 expression levels were manipulated in airway cells using an overexpression plasmid and siRNA technologies. Successful modulation of ORMDL3 was confirmed at both the gene and protein level. The functional impact of modulation of ORMDL3 expression levels on inflammatory responses and activation of the UPR were quantified using complementary cellular and molecular immunology techniques.

Results

Cells with altered ORMDL3 levels responded equally well to innate immune stimuli and produced similar levels of pro-inflammatory cytokines compared to wild-type cells. Treatment with ER stress inducers, thapsigargin and tunicamycin, resulted in activation of the unfolded protein response (UPR). However, we observed no difference in UPR activation in cells with ORMDL3 knockdown compared to cells with normal ORMDL3 levels.

Conclusions

Our results suggest that ORMDL3 variation in the airway epithelium is unlikely to play a significant role in modulating innate immune responses and the UPR in the lung.

Differential gene expression profile of first-generation and second-generation rapamycin-resistant allogeneic T cells

BACKGROUND AIMS

We completed a phase II clinical trial evaluating rapamycin-resistant allogeneic T cells (T-rapa) and now have evaluated a T-rapa product manufactured in 6 days (T-rapa(6)) rather than 12 days (T-Rapa(12)).

METHODS

Using gene expression microarrays, we addressed our hypothesis that the two products would express a similar phenotype. The products had similar phenotypes using conventional comparison methods of cytokine secretion and surface markers.

RESULTS

Unsupervised analysis of 34,340 genes revealed that T-rapa(6) and T-rapa(12) products clustered together, distinct from culture input CD4(+) T cells. Statistical analysis of T-rapa(6) products revealed differential expression of 19.3% of genes (n = 6641) compared with input CD4(+) cells; similarly, 17.8% of genes (n = 6147) were differentially expressed between T-rapa(12) products and input CD4(+) cells. Compared with input CD4(+) cells, T-rapa(6) and T-rapa(12) products were similar in terms of up-regulation of major gene families (cell cycle, stress response, glucose catabolism, DNA metabolism) and down-regulation (inflammatory response, immune response, apoptosis, transcriptional regulation). However, when directly compared, T-rapa(6) and T-rapa(12) products showed differential expression of 5.8% of genes (n = 1994; T-rapa(6) vs. T-rapa(12)).

CONCLUSIONS

Second-generation T-rapa(6) cells possess a similar yet distinct gene expression profile relative to first-generation T-rapa(12) cells and may mediate differential effects after adoptive transfer.

Nr4a receptors are essential for thymic regulatory T cell development and immune homeostasis

Regulatory T cells (T(reg) cells) develop from progenitor thymocytes after the engagement of T cell antigen receptors (TCRs) with high-affinity ligands, but the underlying molecular mechanisms are still unclear. Here we show that the Nr4a nuclear receptors, which are encoded by immediate-early genes upregulated by TCR stimulation in thymocytes, have essential roles in T(reg) cell development. Mice that lacked all Nr4a factors could not produce T(reg) cells and died early owing to systemic autoimmunity. Nr4a receptors directly activated the promoter of the gene encoding the transcription factor Foxp3, and forced activation of Nr4a receptors bypassed low-strength TCR signaling to drive the T(reg) cell developmental program. Our results suggest that Nr4a receptors have key roles in determining CD4(+) T cell fates in the thymus and thus contribute to immune homeostasis.

Nr4a receptors are essential for thymic regulatory T cell development and immune homeostasis

Regulatory T cells (T(reg) cells) develop from progenitor thymocytes after the engagement of T cell antigen receptors (TCRs) with high-affinity ligands, but the underlying molecular mechanisms are still unclear. Here we show that the Nr4a nuclear receptors, which are encoded by immediate-early genes upregulated by TCR stimulation in thymocytes, have essential roles in T(reg) cell development. Mice that lacked all Nr4a factors could not produce T(reg) cells and died early owing to systemic autoimmunity. Nr4a receptors directly activated the promoter of the gene encoding the transcription factor Foxp3, and forced activation of Nr4a receptors bypassed low-strength TCR signaling to drive the T(reg) cell developmental program. Our results suggest that Nr4a receptors have key roles in determining CD4(+) T cell fates in the thymus and thus contribute to immune homeostasis.

STAT6 deficiency ameliorates severity of oxazolone colitis by decreasing expression of claudin-2 and Th2-inducing cytokines

Patients suffering from ulcerative colitis (UC) exhibit chronic colonic inflammation caused by a dysregulated mucosal immune response and epithelial barrier disruption. Th2 cytokines, including IL-13, have been implicated in the pathogenesis of UC. IL-13 induces phosphorylation of STAT6, and we previously demonstrated increased epithelial p-STAT6 in children with UC. In this study, we investigated the role of STAT6 in oxazolone colitis, a murine model of UC, by inducing colitis in STAT6-deficient (STAT6(-/-)) and wild type (WT) mice. We observed increased epithelial cell, T cell, macrophage, and NKT cell STAT6 phosphorylation, as well as increased p-STAT6(+) IL-13-producing NKT cells, in colitic WT mice. Colitis was attenuated in STAT6(-/-) mice, with improvements in weight, colon length, and histopathology. There was decreased induction of the pore-forming tight junction protein claudin-2 in STAT6(-/-) mice. Similarly, short hairpin RNA STAT6 knockdown reduced claudin-2 induction and transepithelial resistance decrease in IL-13-treated human T84 cells. Tissue expression of IL-13, IFN-γ, IL-17, and IL-10 mRNA was similarly induced in WT and STAT6(-/-) colitic mice; however, we observed increased mRNA expression for the Th2-inducing cytokines IL-33 and thymic stromal lymphopoietin in WT mice with colitis, which was abrogated in STAT6(-/-) mice. Mesenteric lymph node cells from STAT6(-/-) mice with colitis exhibited reduced secretion of IL-4, IL-5, IL-13, and IFN-γ. IL-33 augmented mesenteric lymph node cell secretion of IL-5, IL-13, IL-6, and IFN-γ. These data implicate STAT6 in the pathogenesis of colitis in vivo with important roles in altering epithelial barrier function and regulating Th2-inducing cytokine production.

The evolutionary role of the IL-33/ST2 system in host immune defence

Interleukin (IL)-33 is a recently identified pleiotropic cytokine, which can orchestrate complex innate and adaptive immune responses in immunity and disease. It has been characterized as a cytokine of the IL-1 family and affects a wide range of immune cells by signalling through its receptor ST2L. Accumulating evidence suggests a crucial role of IL-33/ST2 in inducing and modifying host immune responses against a variety of pathogens including parasites, bacteria, viruses and fungi as well as sterile insults of both endogenous and exogenous source. In this review, we endeavour to give a comprehensive overview of the current knowledge about the role of IL-33 and its receptor ST2 in host defence against infections.

The influence of commensal bacteria-derived signals on basophil-associated allergic inflammation

Commensal bacteria that colonize mammalian mucosal surfaces are reported to influence T helper type 2 (TH 2) cytokine-dependent inflammation and susceptibility to allergic disease. However, the mechanisms that underlie these observations are only beginning to be understood. We recently utilized studies of murine model systems and atopic patient populations to elucidate a mechanism by which commensal bacteria-derived signals limit serum immunoglobulin E levels, influence basophil development and steady-state circulating basophil populations and regulate basophil-associated TH 2 cell responses and allergic inflammation. In this addendum, we summarize the findings of our recent work and other developments in the field, discuss the broader implications of these findings and generate new hypotheses regarding our understanding of host-commensal relationships. These areas of investigation may be applicable to the development of new preventative or therapeutic approaches to reduce the burden of allergic disease.

Transcription factor IRF4 drives dendritic cells to promote Th2 differentiation

Atopic asthma is an inflammatory pulmonary disease associated with Th2 adaptive immune responses triggered by innocuous antigens. While dendritic cells (DCs) are known to shape the adaptive immune response, the mechanisms by which DCs promote Th2 differentiation remain elusive. Herein we demonstrate that Th2-promoting stimuli induce DC expression of IRF4. Mice with conditional deletion of Irf4 in DCs show a dramatic defect in Th2-type lung inflammation, yet retain the ability to elicit pulmonary Th1 antiviral responses. Using loss- and gain-of-function analysis, we demonstrate that Th2 differentiation is dependent on IRF4 expression in DCs. Finally, IRF4 directly targets and activates the Il-10 and Il-33 genes in DCs. Reconstitution with exogenous IL-10 and IL-33 recovers the ability of Irf4-deficient DCs to promote Th2 differentiation. These findings reveal a regulatory module in DCs by which IRF4 modulates IL-10 and IL-33 cytokine production to specifically promote Th2 differentiation and inflammation.

Interleukin-4-induced β-catenin regulates the conversion of macrophages to multinucleated giant cells

The cytokine interleukin-4 (IL-4) exerts pleiotropic effects on macrophages as it plays a key role in the immune response to infectious agents, allergens, and vaccines. Macrophages exposed to IL-4 drastically change their gene expression and metabolic state to adjust to new functional requirements. IL-4 also induces macrophages to fuse together and form multinucleated giant cells (MGCs). MGC formation is associated with chronic inflammation resulting from persistence of pathogenic microorganisms or foreign materials in tissues. Very little is known, however, about the mechanisms regulating IL-4-induced macrophage-to-MGC conversion. We observed a dramatic increase in β-catenin protein but not mRNA amount in mouse macrophages following exposure to IL-4. To investigate the role of β-catenin in macrophages, we generated mice with a myeloid cell-specific deletion of the β-catenin gene. Ablation of β-catenin expression did not affect the viability of macrophages or impair expression of known IL-4-inducible genes. Intriguingly, β-catenin-deficient macrophages incubated with IL-4 formed MGCs with markedly greater efficiency than wild-type macrophages. Similar increases in multinucleated cell formation were detected in the peritoneal cavity of myeloid cell-specific β-catenin knockout mice injected with chitin, which is known to induce endogenous IL-4 production. Our findings reveal β-catenin as a novel regulator of macrophage responses to IL-4, and suggest that therapeutic modulation of its expression or function may help enhance the effectiveness or ameliorate the pathology of IL-4-driven immune responses.

IL-33 citrine reporter mice reveal the temporal and spatial expression of IL-33 during allergic lung inflammation

Interleukin-33 (IL-33) is an IL-1 family cytokine that signals via its receptor T1/ST2, and is a key regulator of inflammation, notably the type-2 response implicated in allergic asthma. Critical to our understanding of the role of IL-33 is the identification of the cellular sources of IL-33. Although progress has been made in this area, the development of a robust live cell reporter of expression would allow the localisation of IL-33 during ongoing immune responses. We have generated a fluorescent reporter mouse line, Il33^Cit/+, to define the expression profile of IL-33 in vivo and demonstrate its temporal and spatial expression during experimental allergic asthma responses. We found that type-2 pneumocytes constitute the major source of IL-33 upon allergic lung inflammation following exposure to OVA, fungal extract or ragweed pollen. Using Il33^Cit/Cit mice (IL-33-deficient), we establish a role for IL-33 early in the initiation of type-2 responses and the induction of nuocytes (ILC2). We also demonstrate a potential mechanism of action by which IL-33 rapidly initiates type-2 immune responses. Il33^Cit/+ mice have enabled new insights into the initiation of type-2 responses and will provide an important tool for further dissection of this important inflammatory pathway in vivo.

Deficiency of annexin A1 in CD4+ T cells exacerbates T cell-dependent inflammation

Annexin A1 (AnxA1) is recognized as an endogenous anti-inflammatory molecule. However, its effects on the adaptive immune response and, in particular, on T cells remain unclear. In this study, we investigated the actions of AnxA1 in three distinct models of T cell-mediated inflammation. In contact hypersensitivity, collagen-induced arthritis, and inflammation induced by OT-II TCR transgenic T cells responding to OVA, AnxA1 deficiency significantly increased Ag-induced T cell proliferation and the resultant level of inflammation. In the contact hypersensitivity model, this was associated with increased adhesion of CD4(+) T cells, CD8(+) T cells, and neutrophils in the dermal microvasculature, as well as increased T cell expression of RORγt and IL-17A. In collagen-induced arthritis, deficiency of endogenous AnxA1 increased susceptibility to arthritis and Ag-specific T cell activation. Deficiency of AnxA1 also increased OVA-induced cutaneous delayed-type hypersensitivity and IFN-γ and IL-17 release. Transfer experiments using CD4(+) T cells from AnxA1(-/-) mice demonstrated that the absence of AnxA1 solely in T cells resulted in increased inflammatory responses in wild-type recipients. Similarly, experiments using AnxA1(-/-) OT-II CD4(+) T cells demonstrated that the absence of AnxA1 in T cells was sufficient to induce increased Ag-specific CD4(+) T cell proliferation in vivo, augment T cell production of IFN-γ, IL-17, TNF, and IL-6, and increase Akt, ERK, and p38 activation. Together, these findings indicate that T cell-expressed AnxA1 functions to attenuate T cell-driven inflammatory responses via T cell-intrinsic effects on intracellular signaling, proliferation, and Th1/Th17 cytokine release.

Absence of signaling into CD4⁺ cells via C3aR and C5aR enables autoinductive TGF-β1 signaling and induction of Foxp3⁺ regulatory T cells

C3a and C5a receptor (C3aR and C5aR) signaling by dendritic cells and CD4⁺ cells provides costimulatory and survival signals to T effector cells. Here, we demonstrate that when C3aR and C5aR signals are not transduced into CD4⁺ cells, PI-3Kγ-AKT-mTOR signaling ceases, PKA activation increases, auto-inductive transforming growth factor- β1 (TGF-β1) signaling initiates, and CD4⁺ cells become Foxp3⁺ T regulatory cells (iT_regs). Endogenous TGF-β1 suppresses C3aR and C5aR signaling by preventing C3a and C5a production and upregulating C5L2, an alternate C5a receptor. Absent C3aR and C5aR signaling decreases costimulatory molecule and interleukin-6 production and augments interleukin-10 production. The resulting iT_regs exert robust suppression, possess enhanced stability, and suppress ongoing autoimmune disease. Human iT_regs with potent suppressor activity can be induced exploiting this insight.

Essential contribution of IRF3 to intestinal homeostasis and microbiota-mediated Tslp gene induction

The large intestinal epithelial cells and immune cells are exposed to a variety of molecules derived from commensal microbiota that can activate innate receptors, such as Toll-like receptors (TLRs) and retinoic acid-inducible gene-I-like receptors (RLRs). Although the activation of these receptors is known to be critical for homeostasis of the large intestine, the underlying gene regulatory mechanisms are not well understood. Here, we show that IFN regulatory factor (IRF)3 is critical for the suppression of dextran sulfate sodium-induced colitis. IRF3-deficient mice exhibited lethal defects in the inflammatory and recovery phases of the colitis, accompanied by marked defects in the gene induction for thymic stromal lymphopoietin (TSLP), a cytokine known to be essential for protection of the large intestine. We further provide evidence that DNA and RNA of the large intestinal contents are critical for Tslp gene induction via IRF3 activation by cytosolic nucleic acid receptors. We also demonstrate that IRF3 indeed activates the gene promoter of Tslp via IRF-binding sequences. This newly identified intestinal gene regulatory mechanism, wherein IRF3 activated by microbiota-derived nucleic acids plays a critical role in intestinal homeostasis, may have clinical implication in colonic inflammatory disorders.

Minocycline blocks asthma-associated inflammation in part by interfering with the T cell receptor-nuclear factor κB-GATA-3-IL-4 axis without a prominent effect on poly(ADP-ribose) polymerase

Minocycline protects against asthma independently of its antibiotic function and was recently reported as a potent poly(ADP-ribose) polymerase (PARP) inhibitor. In an animal model of asthma, a single administration of minocycline conferred excellent protection against ovalbumin-induced airway eosinophilia, mucus hypersecretion, and Th2 cytokine production (IL-4/IL-5/IL-12(p70)/IL-13/GM-CSF) and a partial protection against airway hyperresponsiveness. These effects correlated with pronounced reduction in lung and sera allergen-specific IgE. A reduction in poly(ADP-ribose) immunoreactivity in the lungs of minocycline-treated/ovalbumin-challenged mice correlated with decreased oxidative DNA damage. The effect of minocycline on PARP may be indirect, as the drug failed to efficiently block direct PARP activation in lungs of N-methyl-N'-nitro-N-nitroso-guanidine-treated mice or H(2)O(2)-treated cells. Minocycline blocked allergen-specific IgE production in B cells potentially by modulating T cell receptor (TCR)-linked IL-4 production at the mRNA level but not through a modulation of the IL-4-JAK-STAT-6 axis, IL-2 production, or NFAT1 activation. Restoration of IL-4, ex vivo, rescued IgE production by minocycline-treated/ovalbumin-stimulated B cells. IL-4 blockade correlated with a preferential inhibition of the NF-κB activation arm of TCR but not GSK3, Src, p38 MAPK, or ERK1/2. Interestingly, the drug promoted a slightly higher Src and ERK1/2 phosphorylation. Inhibition of NF-κB was linked to a complete blockade of TCR-stimulated GATA-3 expression, a pivotal transcription factor for IL-4 expression. Minocycline also reduced TNF-α-mediated NF-κB activation and expression of dependent genes. These results show a potentially broad effect of minocycline but that it may block IgE production in part by modulating TCR function, particularly by inhibiting the signaling pathway, leading to NF-κB activation, GATA-3 expression, and subsequent IL-4 production.

Apple polyphenols suppress antigen presentation of ovalbumin by THP-1-derived dendritic cells

Apple polyphenol extract (AP) and procyanidin contained in AP were investigated for their immunomodulatory effects using THP-1-derived human dendritic cells (TDDCs). The expression levels of HLA-DR (MHC class II) and CD86 (costimulatory molecule) were measured as an indicator of antigen presentation in TDDCs. A significant decrease in HLA-DR expression was observed in the AP and fractionated procyanidin-treated cells in the presence of ovalbumin (OVA), but no effect on CD86 expression was observed. The uptake of OVA was not inhibited by AP treatment, and the gene expression of membrane-associated RING-CH ubiquitin E3 ligase, MARCH1, was up-regulated by AP treatment. It can therefore be presumed that AP suppresses HLA-DR expression via the ubiquitin-proteasome pathway. Furthermore, the up-regulation of IL-12 and TNF-α was found in the procyanidin trimers-treated cells in the presence of OVA. These results suggest that apple polyphenols would be an effective factor for the development of immunomodulatory agents with suppressive effects of antigen presentation.

Interleukin 33 mediates type 2 immunity and inflammation in the central nervous system of mice infected with Angiostrongylus cantonensis

Angiostrongylus cantonensis can induce central nervous system (CNS) injury and cause human eosinophilic meningitis. The CNS has been found to have high expression of interleukin 33 (IL-33), which promotes the pathogenesis of T-helper 2 (Th2)-related disease. Given the predominantly type 2 response induced by A. cantonensis-infected mice and human, it is likely that IL-33 may play a role in aiding this process. We report here that IL-33 protein and ST2L messenger RNA (mRNA) transcripts in the brains were upregulated during A. cantonensis infection and that both splenocytes and brain mononuclear cells became IL-33 responsive and produced interleukin 5 and interleukin 13. Furthermore, administration of IL-33 to A. cantonensis-infected mice enhanced ST2L expression and cytokine production. Interestingly, brain IL-33 protein and ST2L mRNA levels were elevated 14-21 days after infection in BALB/c mice, compared with C57BL/6 mice. Thus, our data indicate that IL-33 produced in the brain may function as an inflammatory mediator in eosinophilic meningitis induced by A. cantonensis.

Immunity to the model intestinal helminth parasite Heligmosomoides polygyrus

Heligmosomoides polygyrus is a natural intestinal parasite of mice, which offers an excellent model of the immunology of gastrointestinal helminth infections of humans and livestock. It is able to establish long-term chronic infections in many strains of mice, exerting potent immunomodulatory effects that dampen both protective immunity and bystander reactions to allergens and autoantigens. Immunity to the parasite develops naturally in some mouse strains and can be induced in others through immunization; while the mechanisms of protective immunity are not yet fully defined, both antibodies and a host cellular component are required, with strongest evidence for a role of alternatively activated macrophages. We discuss the balance between resistance and susceptibility in this model system and highlight new themes in innate and adaptive immunity, immunomodulation, and regulation of responsiveness in helminth infection.

The transcription factor T-bet is induced by multiple pathways and prevents an endogenous Th2 cell program during Th1 cell responses

T-bet is a critical transcription factor for T helper 1 (Th1) cell differentiation. To study the regulation and functions of T-bet, we developed a T-bet-ZsGreen reporter mouse strain. We determined that interleukin-12 (IL-12) and interferon-γ (IFN-γ) were redundant in inducing T-bet in mice infected with Toxoplasma gondii and that T-bet did not contribute to its own expression when induced by IL-12 and IFN-γ. By contrast, T-bet and the transcription factor Stat4 were critical for IFN-γ production whereas IFN-γ signaling was dispensable for inducing IFN-γ. Loss of T-bet resulted in activation of an endogenous program driving Th2 cell differentiation in cells expressing T-bet-ZsGreen. Genome-wide analyses indicated that T-bet directly induced many Th1 cell-related genes but indirectly suppressed Th2 cell-related genes. Our study revealed redundancy and synergy among several Th1 cell-inducing pathways in regulating the expression of T-bet and IFN-γ, and a critical role of T-bet in suppressing an endogenous Th2 cell-associated program.

Cytokines of the γ(c) family control CD4+ T cell differentiation and function

Naive CD4(+) T cells undergo massive proliferation and differentiation into at least four distinct helper T cell subsets after recognition of foreign antigen-derived peptides presented by dendritic cells. Each helper T cell subset expresses a distinct set of genes that encode unique transcription factor(s), as well as hallmark cytokines. The cytokine environment created by activated CD4(+) T cells, dendritic cells and/or other cell types during the course of differentiation is a major determinant for the helper T cell fate. This Review focuses on the role of cytokines of the common γ-chain (γ(c)) family in the determination of the effector helper T cell phenotype that naive CD4(+) T cells adopt after being activated and in the function of these helper T cells.

Elevated antigen-driven IL-9 responses are prominent in peanut allergic humans

Food allergies, and peanut allergy in particular, are leading causes of anaphylactic fatalities worldwide. The immune mechanisms that underlie food allergy remain ill-defined and controversial, in part because studies in humans typically focus on analysis of a limited number of prototypical Th1/Th2 cytokines. Here we determine the kinetics and prevalence of a broad panel of peanut-driven cytokine and chemokine responses in humans with current peanut allergy vs those with stable, naturally occurring clinical tolerance to peanut. Our primary focus is identification of novel indicators of immune dysregulation. Antigen-specific cytokine mRNA and protein responses were elicited in primary culture via peanut or irrelevant antigen (Leishmania extract, milk antigens) mediated stimulation of fresh peripheral blood cells from 40 individuals. Peanut extract exposure in vitro induced a broad panel of responses associated with Th2/Th9-like, Th1-like and Th17-like immunity. Peanut-dependent Type 2 cytokine responses were frequently found in both peanut allergic individuals and those who exhibit clinical tolerance to peanut ingestion. Among Th2/Th9-associated cytokines, IL-9 responses discriminated between allergic and clinically tolerant populations better than did commonly used IL-4, IL-5 or IL-13 responses. Comparison with responses evoked by unrelated control antigen-mediated stimulation showed that these differences are antigen-dependent and allergen-specific. Conversely, the intensity of IL-12, IL-17, IL-23 and IFN-γ production was indistinguishable in peanut allergic and peanut tolerant populations. In summary, the ability to generate and maintain cytokine responses to peanut is not inherently distinct between allergic and peanut tolerant humans. Quantitative differences in the intensity of cytokine production better reflects clinical phenotype, with optimally useful indicators being IL-9, IL-5, IL-13 and IL-4. Equivalent, and minimal, Ag-dependent pro-inflammatory cytokine levels in both healthy and peanut allergic volunteers argues against a key role for such cytokines in maintenance of clinical tolerance to food antigens in humans.

The transcription factor GATA3 is essential for the function of human type 2 innate lymphoid cells

Type 2 innate lymphoid cells (ILC2s) are part of a large family of ILCs that are important effectors in innate immunity, lymphoid organogenesis, and tissue remodeling. ILC2s mediate parasite expulsion but also contribute to airway inflammation, emphasizing the functional similarity between these cells and Th2 cells. Consistent with this, we report that the transcription factor GATA3 was highly expressed by human ILC2s. CRTH2(+) ILC2s were enriched in nasal polyps of patients with chronic rhinosinusitis, a typical type 2-mediated disease. Nasal polyp epithelial cells expressed TSLP, which enhanced STAT5 activation, GATA3 expression, and type 2 cytokine production in ILC2s. Ectopic expression of GATA3 in Lin(-)CD127(+)CRTH2(-) cells resulted in induction of CRTH2 and the capacity to produce high amounts of type 2 cytokines in response to TSLP plus IL-33. Hence, we identify GATA3, potently regulated by TSLP, as an essential transcription factor for the function of human ILC2s.

STAT6-dependent and -independent mechanisms in Th2 polarization

Th2 cells play a key role in directing immune responses against helminths. Additionally, Th2 cells are crucial for many types of allergic reactions. Whereas the molecular mechanisms underlying the differentiation of other types of Th cells are well understood, Th2 differentiation is still a controversial topic. IL-4 and its downstream transcription factor signal transducer and activator of transcription (STAT)6 are well-known key mediators in Th2 differentiation. The fact that Th2 cells themselves are the most potent source of IL-4 suggests that additional mechanisms promoting the initiation of Th2 differentiation exist. This article gives an overview on STAT6-dependent and -independent mechanisms involved in the process of Th2 polarization, including Notch, mTORC2, IL-2/STAT5, and Wnt. Furthermore, we emphasize the role of STAT6 not only as a transcriptional activator promoting Th2 development, but also in fine-tuning alternative signaling pathways which are involved in the initiation of Th2 polarization.

Clinical severity and epithelial endotypes in chronic rhinosinusitis

BACKGROUND

Chronic rhinosinusitis (CRS) is a heterogeneous disease defined by epithelial inflammation. The link between measures of traditional disease severity and markers of epithelial inflammation is poorly understood as prior research has focused on presence of polyps or degree of eosinophilia. The expression of 3 epithelial derived cytokines implicated in initiation of T-helper 2 (Th2) inflammation and an eosinophil chemoattractant were compared with clinical measures used in CRS.

METHODS

Sinus mucosal samples from CRS patients undergoing sinus surgery were analyzed for interleukin-25 (IL-25), IL-33, thymic stromal lymphopoietin (TSLP), and eotaxin-3 messenger RNA (mRNA) expression by quantitative polymerase chain reaction (PCR). Tumor patients undergoing surgery transnasally with normal sinus mucosa were controls. Gene expression was compared with symptom, radiology, and endoscopy scores, serological markers, presence of reactive airways disease (RAD), and atopy.

RESULTS

Thirty-seven patients (38% female, mean age 48 ± 15 years), 12 CRS with nasal polyps (CRSwNP), 18 CRS without nasal polyps (CRSsNP), and 7 controls were recruited. CRSwNP phenotype predicted elevated IL-25, IL-33, and eotaxin-3 levels. Increased eotaxin-3 correlated with poorer computed tomography (CT) (p = 0.004) and endoscopic scores (p = 0.049). Increased IL-25 correlated with poorer CT scores (p = 0.012) and raised serum eosinophils (p = 0.006). No associations with RAD, atopy, and symptom measures were found. No associations for IL-33 and TSLP were found.

CONCLUSION

Inflammatory mediators of the epithelium in CRS has some correlation with traditional measures of disease burden. Certain epithelial profiles may predict highly dysfunctional epithelial barriers and prospective evaluation of the clinical outcomes from interventions is required. Future endotyping of the epithelium in CRS may be able to provide prognostic information.

Type 2 innate immunity in helminth infection is induced redundantly and acts autonomously following CD11c(+) cell depletion

Infection with gastrointestinal helminths generates a dominant type 2 response among both adaptive (Th2) and innate (macrophage, eosinophil, and innate lymphoid) immune cell types. Two additional innate cell types, CD11c(high) dendritic cells (DCs) and basophils, have been implicated in the genesis of type 2 immunity. Investigating the type 2 response to intestinal nematode parasites, including Heligmosomoides polygyrus and Nippostrongylus brasiliensis, we first confirmed the requirement for DCs in stimulating Th2 adaptive immunity against these helminths through depletion of CD11c(high) cells by administration of diphtheria toxin to CD11c.DOG mice. In contrast, responsiveness was intact in mice depleted of basophils by antibody treatment. Th2 responses can be induced by adoptive transfer of DCs, but not basophils, exposed to soluble excretory-secretory products from these helminths. However, innate type 2 responses arose equally strongly in the presence or absence of CD11c(high) cells or basophils; thus, in CD11c.DOG mice, the alternative activation of macrophages, as measured by expression of arginase-1, RELM-α, and Ym-1 (Chi3L3) in the intestine following H. polygyrus infection or in the lung following N. brasiliensis infection, was unaltered by depletion of CD11c-expressing DCs and alveolar macrophages or by antibody-mediated basophil depletion. Similarly, goblet cell-associated RELM-β in lung and intestinal tissues, lung eosinophilia, and expansion of innate lymphoid ("nuocyte") populations all proceeded irrespective of depletion of CD11c(high) cells or basophils. Thus, while CD11c(high) DCs initiate helminth-specific adaptive immunity, innate type 2 cells are able to mount an autonomous response to the challenge of parasite infection.

Thymic stromal lymphopoietin-dependent basophils promote Th2 cytokine responses following intestinal helminth infection

CD4(+) Th2 cytokine responses promote the development of allergic inflammation and are critical for immunity to parasitic helminth infection. Recent studies highlighted that basophils can promote Th2 cytokine-mediated inflammation and that phenotypic and functional heterogeneity exists between classical IL-3-elicited basophils and thymic stromal lymphopoietin (TSLP)-elicited basophils. However, whether distinct basophil populations develop after helminth infection and their relative contributions to anti-helminth immune responses remain to be defined. After Trichinella spiralis infection of mice, we show that basophil responses are rapidly induced in multiple tissue compartments, including intestinal-draining lymph nodes. Trichinella-induced basophil responses were IL-3-IL-3R independent but critically dependent on TSLP-TSLPR interactions. Selective depletion of basophils after Trichinella infection impaired infection-induced CD4(+) Th2 cytokine responses, suggesting that TSLP-dependent basophils augment Th2 cytokine responses after helminth infection. The identification and functional classification of TSLP-dependent basophils in a helminth infection model, coupled with their recently described role in promoting atopic dermatitis, suggests that these cells may be a critical population in promoting Th2 cytokine-associated inflammation in a variety of inflammatory or infectious settings. Collectively, these data suggest that the TSLP-basophil pathway may represent a new target in the design of therapeutic intervention strategies to promote or limit Th2 cytokine-dependent immunity and inflammation.

An inhibitory role for Sema4A in antigen-specific allergic asthma

PURPOSE

The class IV semaphorin Sema4A is critical for efficient Th1 differentiation and Sema4a (-/-) mice exhibit impaired Th1 immune responses. However, the role of Sema4A in Th2 cell-mediated allergic diseases has not been fully studied. The aim of this study was to clarify the regulatory role possessed by Sema4A in mouse models of allergic diseases, particularly allergic asthma.

METHODS

Sema4a (-/-) mice on a BALB/c background were examined for the development of allergic diseases. To induce experimental asthma, mice were sensitized with ovalbumin (OVA) followed by intranasal challenges with OVA. After challenge, airway hyperreactivity (AHR) and airway inflammation were evaluated. The role of Sema4A in asthma was examined using Sema4a (-/-) mice and Sema4A-Fc fusion proteins. The direct effects of Sema4A-Fc on antigen-specific effector CD4(+) T cells were also examined.

RESULTS

A fraction of Sema4a (-/-) BALB/c mice spontaneously developed skin lesions that resembled atopic dermatitis (AD) in humans. Furthermore, AHR, airway inflammation, and Th2-type immune responses were enhanced in Sema4a (-/-) mice compared to wild type (WT) mice when immunized and challenged with OVA. In vivo systemic administration of Sema4A-Fc during the challenge period ameliorated AHR and lung inflammation and reduced the production of Th2-type cytokines in WT mice. The inhibitory effects of Sema4A on airway inflammation were also observed in mice deficient in Tim-2, a Sema4A receptor. Finally, we showed that Sema4A-Fc directly inhibited IL-4-producing OVA-specific CD4(+) T cells.

CONCLUSION

These results demonstrate that Sema4A plays an inhibitory role in Th2-type allergic diseases, such as allergic asthma.

IL-33, but not thymic stromal lymphopoietin or IL-25, is central to mite and peanut allergic sensitization

BACKGROUND

Allergen exposure at lung and gut mucosae can lead to aberrant T(H)2 immunity and allergic disease. The epithelium-associated cytokines thymic stromal lymphopoietin (TSLP), IL-25, and IL-33 are suggested to be important for the initiation of these responses.

OBJECTIVE

We sought to investigate the contributions of TSLP, IL-25, and IL-33 in the development of allergic disease to the common allergens house dust mite (HDM) or peanut.

METHODS

Neutralizing antibodies or mice deficient in TSLP, IL-25, or IL-33 signaling were exposed to HDM intranasally or peanut intragastrically, and immune inflammatory and physiologic responses were evaluated. In vitro assays were performed to examine specific dendritic cell (DC) functions.

RESULTS

We showed that experimental HDM-induced allergic asthma and food allergy and anaphylaxis to peanut were associated with TSLP production but developed independently of TSLP, likely because these allergens functionally mimicked TSLP inhibition of IL-12 production and induction of OX40 ligand (OX40L) on DCs. Blockade of OX40L significantly lessened allergic responses to HDM or peanut. Although IL-25 and IL-33 induced OX40L on DCs in vitro, only IL-33 signaling was necessary for intact allergic immunity, likely because of its superior ability to induce DC OX40L and expand innate lymphoid cells in vivo.

CONCLUSION

These data identify a nonredundant, IL-33-driven mechanism initiating T(H)2 responses to the clinically relevant allergens HDM and peanut. Our findings, along with those in infectious and transgenic/surrogate allergen systems, favor a paradigm whereby multiple molecular pathways can initiate T(H)2 immunity, which has implications for the conceptualization and manipulation of these responses in health and disease.

JAK Kinases in Health and Disease: An Update

Janus kinases (Jaks) are critical signaling elements for a large subset of cytokines. As a consequence they play pivotal roles in the patho-physiology of many diseases including neoplastic and autoimmune diseases. Small molecule Jak inhibitors as therapeutic agents have become a reality and the palette of such inhibitors will likely expand. This review will summarize our current knowledge on these key enzymes and their associated pharmaceutical inhibitors.

Human schistosome infection and allergic sensitisation

Several field studies have reported an inverse relationship between the prevalence of helminth infections and that of allergic sensitisation/atopy. Recent studies show that immune responses induced by helminth parasites are, to an extent, comparable to allergic sensitisation. However, helminth products induce regulatory responses capable of inhibiting not only antiparasite immune responses, but also allergic sensitisation. The relative effects of this immunomodulation on the development of protective schistosome-specific responses in humans has yet to be demonstrated at population level, and the clinical significance of immunomodulation of allergic disease is still controversial. Nonetheless, similarities in immune responses against helminths and allergens pose interesting mechanistic and evolutionary questions. This paper examines the epidemiology, biology and immunology of allergic sensitisation/atopy, and schistosome infection in human populations.

Innate immunostimulatory properties of allergens and their relevance to food allergy

Food allergy is an increasingly prevalent disease of immune dysregulation directed to a small subset of proteins. Shared structural and functional features of allergens, such as glycosylation, lipid-binding and protease activity may provide insight into the mechanisms involved in the induction of primary Th2 immune responses. We review the literature of innate Th2-type immune activation as a context for better understanding the properties of allergens that contribute to the induction of Th2-biased immune responses in at least a subset of individuals. Th2-priming signals have been largely identified in the context of parasite immunity and wound healing. Some of the features of parasite antigens and the innate immune responses to them are now understood to play a role in allergic inflammation as well. These include both exogenous and endogenous activators of innate immunity and subsequent release of key cytokine mediators such as thymic stromal lymphopoietin (TSLP), interleukin (IL)-25 and IL-33. Moreover, numerous innate immune cells including epithelium, dendritic cells, basophils, innate lymphoid cells and others all interact to shape the adaptive Th2 immune response. Progress toward understanding Th2-inducing innate immune signals more completely may lead to novel strategies for primary prevention and therapy of respiratory and food allergies.

New paradigms in type 2 immunity

Nearly half of the world's population harbors helminth infections or suffers from allergic disorders. A common feature of this population is the so-called "type 2 immune response," which confers protection against helminths, but also promotes pathologic responses associated with allergic inflammation. However, the mechanisms that initiate and control type 2 responses remain enigmatic. Recent advances have revealed a role for the innate immune system in orchestrating type 2 responses against a bewildering array of stimuli, from nanometer-sized allergens to 20-meter-long helminth parasites. Here, we review these advances and suggest that the human immune system has evolved multiple mechanisms of sensing such stimuli, from recognition of molecular patterns via innate immune receptors to detecting metabolic changes and tissue damage caused by these stimuli.