Listeria hijacks host mitophagy through a novel mitophagy receptor to evade killing.

Cells use mitophagy to remove damaged or unwanted mitochondria to maintain homeostasis. Here we report that the intracellular bacterial pathogen Listeria monocytogenes exploits host mitophagy to evade killing. We found that L. monocytogenes induced mitophagy in macrophages through the virulence factor listeriolysin O (LLO). We discovered that NLRX1, the only Nod-like receptor (NLR) family member with a mitochondrial targeting sequence, contains an LC3-interacting region (LIR) and directly associated with LC3 through the LIR. NLRX1 and its LIR motif were essential for L. monocytogenes-induced mitophagy. NLRX1 deficiency and use of a mitophagy inhibitor both increased mitochondrial production of reactive oxygen species and thereby suppressed the survival of L. monocytogenes. Mechanistically, L. monocytogenes and LLO induced oligomerization of NLRX1 to promote binding of its LIR motif to LC3 for induction of mitophagy. Our study identifies NLRX1 as a novel mitophagy receptor and discovers a previously unappreciated strategy used by pathogens to hijack a host cell homeostasis system for their survival.

Dysregulated Lung Commensal Bacteria Drive Interleukin-17B Production to Promote Pulmonary Fibrosis through Their Outer Membrane Vesicles.

Idiopathic pulmonary fibrosis (IPF) is a severe form of lung fibrosis with a high mortality rate. However, the etiology of IPF remains unknown. Here, we report that alterations in lung microbiota critically promote pulmonary fibrosis pathogenesis. We found that lung microbiota was dysregulated, and the dysregulated microbiota in turn induced production of interleukin-17B (IL-17B) during bleomycin-induced mouse lung fibrosis. Either lung-microbiota depletion or IL-17B deficiency ameliorated the disease progression. IL-17B cooperated with tumor necrosis factor-α to induce expression of neutrophil-recruiting genes and T helper 17 (Th17)-cell-promoting genes. Three pulmonary commensal microbes, which belong to the genera Bacteroides and Prevotella, were identified to promote fibrotic pathogenesis through IL-17R signaling. We further defined that the outer membrane vesicles (OMVs) that were derived from the identified commensal microbes induced IL-17B production through Toll-like receptor-Myd88 adaptor signaling. Together our data demonstrate that specific pulmonary symbiotic commensals can promote lung fibrosis by regulating a profibrotic inflammatory cytokine network.

Growth Factor FGF2 Cooperates with Interleukin-17 to Repair Intestinal Epithelial Damage.

The intestinal epithelial barrier plays a critical role in the mucosal immunity. However, it remains largely unknown how the epithelial barrier is maintained after damage. Here we show that growth factor FGF2 synergized with interleukin-17 (IL-17) to induce genes for repairing of damaged epithelium. FGF2 or IL-17 deficiency resulted in impaired epithelial proliferation, increased pro-inflammatory microbiota outgrowth, and consequently worse pathology in a DSS-induced colitis model. The dysregulated microbiota in the model induced transforming growth factor beta 1 (TGFß1) expression, which in turn induced FGF2 expression mainly in regulatory T cells. Act1, an essential adaptor in IL-17 signaling, suppressed FGF2-induced ERK activation through binding to adaptor molecule GRB2 to interfere with its association with guanine nucleotide exchange factor SOS1. Act1 preferentially bound to IL-17 receptor complex, releasing its suppressive effect on FGF2 signaling. Thus, microbiota-driven FGF2 and IL-17 cooperate to repair the damaged intestinal epithelium through Act1-mediated direct signaling cross-talk.

IL-17RE is the functional receptor for IL-17C and mediates mucosal immunity to infection with intestinal pathogens.

Interleukin 17 receptor E (IL-17RE) is an orphan receptor of the IL-17 receptor family. Here we show that IL-17RE is a receptor specific to IL-17C and has an essential role in host mucosal defense against infection. IL-17C activated downstream signaling through IL-17RE-IL-17RA complex for the induction of genes encoding antibacterial peptides as well as proinflammatory molecules. IL-17C was upregulated in colon epithelial cells during infection with Citrobacter rodentium and acted in synergy with IL-22 to induce the expression of antibacterial peptides in colon epithelial cells. Loss of IL-17C-mediated signaling in IL-17RE-deficient mice led to lower expression of genes encoding antibacterial molecules, greater bacterial burden and early mortality during infection. Together our data identify IL-17RE as a receptor of IL-17C that regulates early innate immunity to intestinal pathogens.

Alterations in the microbiota drive interleukin-17C production from intestinal epithelial cells to promote tumorigenesis.

Although the microbiota has been shown to drive production of interleukin-17A (IL-17A) from T helper 17 cells to promote cell proliferation and tumor growth in colorectal cancer, the molecular mechanisms for microbiota-mediated regulation of tumorigenesis are largely unknown. Here, we found that the innate-like cytokine IL-17C was upregulated in human colorectal cancers and in mouse intestinal tumor models. Alterations in the microbiota drove IL-17C upregulation specifically in intestinal epithelial cells (IECs) through Toll-like receptor (TLR)-MyD88-dependent signaling during intestinal tumorigenesis. Microbiota-driven IL-17C induced Bcl-2 and Bcl-xL expression in IECs in an autocrine manner to promote cell survival and tumorigenesis in both chemically induced and spontaneous intestinal tumor models. Thus, IL-17C promotes cancer development by increasing IEC survival, and the microbiota can mediate cancer pathogenesis through regulation of IL-17C.

The impact of lung microbiota dysbiosis on inflammation.

Host-microbiota interaction plays fundamental roles in the homeostasis of mucosal immunity. Dysbiosis of intestinal microbiota has been demonstrated to participate in various immune responses and many multifactorial diseases. Study of intestinal microbiota has moved beyond the consequences of dysbiosis to the causal microbiota associated with diseases. However, studies of pulmonary microbiota and its dysbiosis are still in their infancy. Improvement of culture-dependent and -independent techniques has facilitated our understanding of lung microbiota that not only exists in healthy lung tissue but also exerts great impact on immune responses under both physiological and pathological conditions. In this review, we summarize recent progresses of lung microbiota dysbiosis and its impact on the local immune system that determines the balance of tolerance and inflammation. We discuss the causal roles of pulmonary dysbiosis under disease settings, and propose that the interaction between lung microbiota and host is critical for establishing the immune homeostasis in lung.

IL-17C has a pathogenic role in kidney ischemia/reperfusion injury.

Cytokines are necessary to trigger the inflammatory response in kidney ischemia/reperfusion injury. Interleukin-17C (IL-17C), a unique member of the IL-17 family, is a cytokine produced by epithelial cells implicated in host defense and autoimmune diseases. However, little is known about the role of IL-17C in acute kidney injury. We investigated this and found that IL-17C was significantly increased in kidney biopsies of patients and mice with acute kidney injury. Exposure to hypoxia induced upregulation of IL-17C in kidney tubular epithelial cells. To further investigate the role of IL-17C, kidney ischemia/reperfusion injury was induced in mice. Inhibition of IL-17C action with a neutralizing antibody or IL-17 receptor E (IL-17RE) knockout attenuated tubular injury, kidney oxidative stress, and kidney inflammation. Mechanistically, both IL-17C neutralization and IL-17RE knockout attenuated TH17 activation and IL-17A expression in kidneys of mice with acute kidney injury. TNF-α and IL-1ß, downstream cytokines of IL-17C, were also reduced in IL-17C antibody pretreated and IL-17RE knockout mice. Additionally, IL-17C knockdown with siRNA decreased hypoxia-induced inflammation in kidney tubular cells and silencing IL-17RE abrogated the effects of IL-17C in kidney tubular cells. Thus, IL-17C may participate in the inflammatory response of acute kidney injury and inhibition of IL-17C or blockade of IL-17 RE may be a novel therapeutic strategy for the treatment of acute kidney injury.

IL-17-producing ST2+ group 2 innate lymphoid cells play a pathogenic role in lung inflammation.

BACKGROUND: IL-17 plays a pathogenic role in asthma. ST2- inflammatory group 2 innate lymphoid cells (ILC2s) driven by IL-25 can produce IL-17, whereas ST2+ natural ILC2s produce little IL-17. OBJECTIVE: We characterized ST2+IL-17+ ILC2s during lung inflammation and determined the pathogenesis and molecular regulation of ST2+IL-17+ ILC2s. METHODS: Lung inflammation was induced by papain or IL-33. IL-17 production by lung ILC2s from wild-type, Rag1-/-, Rorcgfp/gfp, and aryl hydrocarbon receptor (Ahr)-/- mice was examined by using flow cytometry. Bone marrow transfer experiments were performed to evaluate hematopoietic myeloid differentiation primary response gene-88 (MyD88) signaling in regulating IL-17 production by ILC2s. mRNA expression of IL-17 was analyzed in purified naive ILC2s treated with IL-33, leukotrienes, and inhibitors for nuclear factor of activated T cells, p38, c-Jun N-terminal kinase, or nuclear factor κ light-chain enhancer of activated B cells. The pathogenesis of IL-17+ ILC2s was determined by transferring wild-type or Il17-/- ILC2s to Rag2-/-Il2rg-/- mice, which further induced lung inflammation. Finally, expression of 106 ILC2 signature genes was compared between ST2+IL-17+ ILC2s and ST2+IL-17- ILC2s. RESULTS: Papain or IL-33 treatment boosted IL-17 production from ST2+ ILC2s (referred to by us as ILC217s) but not ST2- ILC2s. Ahr, but not retinoic acid receptor-related orphan receptor γt, facilitated the production of IL-17 by ILC217s. The hematopoietic compartment of MyD88 signaling is essential for ILC217 induction. IL-33 works in synergy with leukotrienes, which signal through nuclear factor of activated T-cell activation to promote IL-17 in ILC217s. Il17-/- ILC2s were less pathogenic in lung inflammation. ILC217s concomitantly expressed IL-5 and IL-13 but expressed little GM-CSF. CONCLUSION: During lung inflammation, IL-33 and leukotrienes synergistically induce ILC217s. ILC217s are a highly pathogenic and unexpected source for IL-17 in lung inflammation.

MicroRNAs 15A and 16-1 Activate Signaling Pathways That Mediate Chemotaxis of Immune Regulatory B cells to Colorectal Tumors.

BACKGROUND & AIMS: B cells infiltrate tumors, but little is known about how they affect tumor growth and progression. microRNA15A (MIR15A or miRNA15A) and microRNA16-1 (MIR16-1 or miRNA16-1) regulate cell proliferation, apoptosis, and drug resistance. We investigated their involvement in B-cell-mediated immune suppression by colorectal tumors. METHODS: Mice with disruptions of the gene cluster that encodes MIR15A and MIR16-1 (knockout mice), and control (C57BL/B6) mice were given azoxymethane with dextran sodium sulfate (AD) to induce formation of colorectal tumors. Mice were given anti-CD20 to delete B cells, or injections of agomir to increase MIR15A and MIR16-1. Proliferation of CD8+T cells was measured by carboxyfluorescein-succinimidyl-ester analysis. Colon tissues were collected from mice and analyzed by flow cytometry, microRNA (miRNA) sequencing, and for cytokine production. Intestinal epithelial cells (IECs) were isolated and transfected with miRNA mimics, to identify their targets. We analyzed miRNA expression patterns and quantified B cells in colorectal cancer tissue microarrays derived from 90 patients who underwent surgical resection, from July 2006 through April 2008, in Shanghai, China; expression data were compared with clinical outcomes. RESULTS: Tumors that developed in knockout mice following administration of AD were larger and contained greater numbers of B cells than tumors that grew in control mice. Most of the B cells in the tumors were positive for immunoglobulin A (IgA+). IgA+ B cells expressed high levels of immune regulatory molecules (programmed death ligand 1, interleukin 10, and transforming growth factor beta), and repressed the proliferation and activation of CD8+ T cells. Levels of MIR15A and MIR16-1 were reduced in colon tumors from mice, compared with nontumor colon tissue. Incubation of IECs with IL17A reduced expression of MIR15A and MIR16-1. Transgenic expression of MIR15A and MIR16-1 in IECs decreased activation of NF-κB and STAT1 by reducing expression of I-kappaB kinases; this resulted in reduced production of chemokine (C-X-C motif) ligands 9 and 10 and decreased chemotaxis of IgA+ B cells. Tumors in mice injected with AD and agomir grew more slowly than tumors in mice not given in agomir and contained fewer IgA+ B cells. We found a negative correlation between levels of MIR15A and MIR16-1 and numbers of IgA+B cells in human colorectal tumor tissues; high levels of MIR15A and MIR16-1 and low numbers of IgA+B cells were associated with longer survival times of patients. CONCLUSIONS: We found increased levels of MIR15A and MIR16-1 to reduce numbers of IgA+ B cells in colorectal tumor tissues and correlate with increased survival time of patients. In mice that lack MIR15A and MIR16-1, colon tumors grow more rapidly and contain increased numbers of IgA+ B cells. MIR15A and MIR16-1 appear to activate signaling pathways required for B-cell-mediated immune suppression.

NDR1 protein kinase promotes IL-17- and TNF-α-mediated inflammation by competitively binding TRAF3.

Interleukin 17 (IL-17) is an important inducer of tissue inflammation and is involved in numerous autoimmune diseases. However, how its signal transduction is regulated is not well understood. Here, we report that nuclear Dbf2-related kinase 1 (NDR1) functions as a positive regulator of IL-17 signal transduction and IL-17-induced inflammation. NDR1 deficiency or knockdown inhibits the IL-17-induced phosphorylation of p38, ERK1/2, and p65 and the expression of chemokines and cytokines, whereas the overexpression of NDR1 promotes IL-17-induced signaling independent of its kinase activity. Mechanistically, NDR1 interacts with TRAF3 and prevents its binding to IL-17R, which promotes the formation of an IL-17R-Act1-TRAF6 complex and downstream signaling. Consistent with this, IL-17-induced inflammation is significantly reduced in NDR1-deficient mice, and NDR1 deficiency significantly protects mice from MOG-induced experimental autoimmune encephalomyelitis (EAE) and 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced colitis likely by its inhibition of IL-17-mediated signaling pathway. NDR1 expression is increased in the colons of ulcerative colitis (UC) patients. Taken together, these findings suggest that NDR1 is involved in the development of autoimmune diseases.

Th17 differentiation and their pro-inflammation function.

CD4(+) T helper cells are classical but constantly reinterpreted T-cell subset, playing critical roles in a diverse range of inflammatory responses or diseases. Depending on the cytokines they release and the immune responses they mediate, CD4(+) T cells are classically divided into two major cell populations: Th1 and Th2 cells. However, recent studies challenged this Th1/Th2 paradigm by discovering several T-helper cell subsets with specific differentiation program and functions, including Th17 cells, Treg cells, and Tfh cells. In this chapter, we summarize the current understanding and recent progresses on the Th17 lineage differentiation and its effector impacts on variety of inflammatory responses or disease pathogenesis.

The activation and regulation of IL-17 receptor mediated signaling.

Interleukin-17 (IL-17), the signature cytokine produced by T helper 17 (Th17) cells, plays pivotal roles in host defense responses against microbial invasion, as well as in the pathogenesis of autoimmune diseases and allergic syndromes. IL-17 activates several downstream signaling pathways including NF-κB, MAPKs and C/EBPs to induce gene expression of antibacterial peptides, proinflammatory chemokines and cytokines and matrix metalloproteinases (MMPs). IL-17 can also stabilize mRNAs of genes induced by TNFα. Although the physiological and pathological functions of IL-17 have been studied for many years, the landscape of its signaling transduction has not been described until recently. The cytosolic adaptor molecule Act1 (also known as CIKS) is considered as the master mediator of IL-17 signaling. In this review, we will summarize recent progress on activation and regulation of IL-17 mediated signal transduction, especially on Act1 mediated regulation of the signaling.

Triggering endogenous Z-RNA sensing for anti-tumor therapy through ZBP1-dependent necroptosis.

ZBP1 senses viral Z-RNAs to induce necroptotic cell death to restrain viral infection. ZBP1 is also thought to recognize host cell-derived Z-RNAs to regulate organ development and tissue inflammation in mice. However, it remains unknown how the host-derived Z-RNAs are formed and how these endogenous Z-RNAs are sensed by ZBP1. Here, we report that oxidative stress strongly induces host cell endogenous Z-RNAs, and the Z-RNAs then localize to stress granules for direct sensing by ZBP1 to trigger necroptosis. Oxidative stress triggers dramatically increase Z-RNA levels in tumor cells, and the Z-RNAs then directly trigger tumor cell necroptosis through ZBP1. Localization of the induced Z-RNAs to stress granules is essential for ZBP1 sensing. Oxidative stress-induced Z-RNAs significantly promote tumor chemotherapy via ZBP1-driven necroptosis. Thus, our study identifies oxidative stress as a critical trigger for Z-RNA formation and demonstrates how Z-RNAs are directly sensed by ZBP1 to trigger anti-tumor necroptotic cell death.

IL-17/IL-17 receptor system in autoimmune disease: mechanisms and therapeutic potential.

IL-17 (interleukin-17), a hallmark cytokine of Th17 (T-helper 17) cells, plays critical roles in host defence against bacterial and fungal infections, as well as in the pathogenesis of autoimmune diseases. The present review focuses on current knowledge of the regulation, functional mechanisms and targeting strategies of IL-17 in the context of inflammatory autoimmune diseases. Evidence shows that IL-17 is highly up-regulated at sites of inflammatory tissues of autoimmune diseases and amplifies the inflammation through synergy with other cytokines, such as TNF (tumour necrosis factor) α. Although IL-17 was originally thought to be produced mainly by Th17 cells, a newly defined T-cell subset with a specific differentiation programme and tight regulation, several other cell types (especially innate immune cells) are also found as important sources for IL-17 production. Although IL-17 activates common downstream signalling, including NF-κB (nuclear factor κB), MAPKs (mitogen-activated protein kinases), C/EBPs (CCAAT/enhancer-binding proteins) and mRNA stability, the immediate receptor signalling has been shown to be quite unique and tightly regulated. Mouse genetic studies have demonstrated a critical role for IL-17 in the pathogenesis of variety of inflammatory autoimmune diseases, such as RA (rheumatoid arthritis) and MS (multiple sclerosis). Importantly, promising results have been shown in initial clinical trials of monoclonal antibodies against IL-17 or its receptor (IL-17R) to block IL-17-mediated function in treating autoimmune patients with psoriasis, RA and MS. Therefore targeting IL-17/IL-17R, IL-17-producing pathways or IL-17-mediated signalling pathways can be considered for future therapy in autoimmune diseases.

Tumor necrosis factor-α blockade ameliorates diabetic nephropathy in rats.

BACKGROUND: Tubular injury plays a critical role in the development of diabetic nephropathy (DN), but current DN therapies do not combat tubular injury. This study was conducted to investigate if tumor necrosis factor (TNF)-α inhibition protects against tubular injury in diabetic rats and to examine the associated mechanisms. METHODS: Kidney biopsy tissues were collected and analyzed from 12 patients with DN and 5 control subjects. Streptozotocin (STZ)-induced diabetic rats were treated with a TNF-α inhibitor for 12 weeks. Renal function, albuminuria, histological injury, renal TNF-α messenger RNA (mRNA) and the NOD- (nucleotide-binding), LRR- (domain-like receptor) and pyrin domain-containing protein 3 (NLRP3) inflammasome were assessed. RESULTS: Diabetic patients with tubulointerstitial injury (TIN) presented with higher renal tubular expression of TNF-α mRNA and the NLRP3 inflammasome (P < 0.05). TNF-α inhibition reduced albuminuria, glomerular injury and tubular injury in STZ-induced diabetic rats (P < 0.05). Importantly, TNF-α inhibition significantly reduced the NLRP3 inflammasome in tubules (P < 0.05). Moreover, TNF-α inhibition decreased expression of tubular interleukin (IL)-6 and IL-17A mRNA. CONCLUSIONS: TNF-α inhibition protects against TIN by suppressing the NLRP3 inflammasome in DN rats. Future studies may focus on the clinical protective effects of TNF-α inhibition using prospective observation.

An Autocrine Circuit of IL-33 in Keratinocytes Is Involved in the Progression of Psoriasis.

IL-33 is constitutively expressed in the skin. Psoriasis is a common skin inflammatory disease. The roles of IL-33 in psoriasis have not been well-elucidated. We identified that keratinocytes (KCs) are the predominant cells expressing IL-33 and its receptor, suppression of tumorigenicity 2, in the skin. KCs actively released IL-33 on psoriasis inflammatory stimuli and induced psoriasis-related cytokine, chemokine, and inflammatory molecules genes transcription in KCs in an autocrine manner. IL-33‒specific deficiency in KCs ameliorated imiquimod-induced psoriatic dermatitis. In addition, intradermal injection of recombinant IL-33 alone induced psoriasis-like dermatitis, which is attributed to the transcriptional upregulation of genes enriched in IL-17, TNF, and chemokine signaling pathway in KCs on recombinant IL-33 stimulation. Our data demonstrate that the autocrine circuit of IL-33 in KCs promotes the progression of psoriatic skin inflammation, and IL-33 is a potential therapeutic target for psoriasis.

Cathepsin C promotes breast cancer lung metastasis by modulating neutrophil infiltration and neutrophil extracellular trap formation.

Lung metastasis is the major cause of breast cancer-related mortality. The neutrophil-associated inflammatory microenvironment aids tumor cells in metastatic colonization in lungs. Here, we show that tumor-secreted protease cathepsin C (CTSC) promotes breast-to-lung metastasis by regulating recruitment of neutrophils and formation of neutrophil extracellular traps (NETs). CTSC enzymatically activates neutrophil membrane-bound proteinase 3 (PR3) to facilitate interleukin-1ß (IL-1ß) processing and nuclear factor κB activation, thus upregulating IL-6 and CCL3 for neutrophil recruitment. In addition, the CTSC-PR3-IL-1ß axis induces neutrophil reactive oxygen species production and formation of NETs, which degrade thrombospondin-1 and support metastatic growth of cancer cells in the lungs. CTSC expression and secretion are associated with NET formation and lung metastasis in human breast tumors. Importantly, targeting CTSC with compound AZD7986 effectively suppresses lung metastasis of breast cancer in a mouse model. Overall, our findings reveal a mechanism of how tumor cells regulate neutrophils in metastatic niches and support CTSC-targeting approaches for cancer treatment.

Tpl2 Protects Against Fulminant Hepatitis Through Mobilization of Myeloid-Derived Suppressor Cells.

Myeloid derived suppressor cells (MDSC) in the liver microenvironment protects against the inflammation-induced liver injury in fulminant hepatitis (FH). However, the molecular mechanism through which MDSC is recruited into the inflamed liver remain elusive. Here we identified a protein kinase Tpl2 as a critical mediator of MDSC recruitment into liver during the pathogenesis of Propionibacterium acnes/LPS-induced FH. Loss of Tpl2 dramatically suppressed MDSC mobilization into liver, leading to exaggerated local inflammation and increased FH-induced mortality. Mechanistically, although the protective effect of Tpl2 for FH-induced mortality was dependent on the presence of MDSC, Tpl2 neither directly targeted myeloid cells nor T cells to regulate FH pathogenesis, but functioned in hepatocytes to mediate the induction of MDSC-attracting chemokine CXCL1 and CXCL2 through modulating IL-25 (also known as IL-17E) signaling. As a consequence, increased MDSC in the inflamed liver specifically restrained the local proliferation of infiltrated pathogenic CD4+ T cells, and thus protected against the inflammation-induced acute liver failure. Together, our findings established Tpl2 as a critical mediator of MDSC recruitment and highlighted the therapeutic potential of Tpl2 for the treatment of FH.

Dectin-1-induced RIPK1 and RIPK3 activation protects host against Candida albicans infection.

Necroptosis is a recently defined type of programmed cell death with the specific signaling cascade of receptor-interacting protein 1 (RIPK1) and RIPK3 complex to activate the executor MLKL. However, the pathophysiological roles of necroptosis are largely unexplored. Here, we report that fungus triggers myeloid cell necroptosis and this type of cell death contributes to host defense against the pathogen infection. Candida albicans as well as its sensor Dectin-1 activation strongly induced necroptosis in myeloid cells through the RIPK1-RIPK3-MLKL cascade. CARD9, a key adaptor in Dectin-1 signaling, was identified to bridge the RIPK1 and RIPK3 complex-mediated necroptosis pathway. RIPK1 and RIPK3 also potentiated Dectin-1-induced MLKL-independent inflammatory response. Both the MLKL-dependent and MLKL-independent pathways were required for host defense against C. albicans infection. Thus, our study demonstrates a new type of host defense system against fungal infection.

USP38 critically promotes asthmatic pathogenesis by stabilizing JunB protein.

Th2 immune response is critical for allergic asthma pathogenesis. Molecular mechanisms for regulating Th2 immunity are still not well understood. Here we report that the ubiquitin-specific protease USP38 is crucial for Th2-mediated allergic asthma. TCR stimulation up-regulated the USP38 level, and USP38 in turn mediated the protein stabilization of JunB, a transcription factor specific for Th2 development. Consequently, USP38 was specifically required for TCR-induced production of Th2 cytokines and Th2 development both in vitro and in vivo, and USP38-deficient mice were resistant to asthma pathogenesis induced by OVA or HDM. Mechanistically, USP38 directly associated with JunB, deubiquitinated Lys-48-linked poly-ubiquitination of JunB, and consequently blocked TCR-induced JunB turnover. USP38 represents the first identified deubiquitinase specifically for Th2 immunity and the associated asthma.