Suppression of Type I Interferon Signaling in Myeloid Cells by Autoantibodies in Severe COVID-19 Patients

PURPOSE

Auto-antibodies (auto-abs) to type I interferons (IFNs) have been identified in patients with life-threatening coronavirus disease 2019 (COVID-19), suggesting that the presence of auto-abs may be a risk factor for disease severity. We therefore investigated the mechanism underlying COVID-19 exacerbation induced by auto-abs to type I IFNs.

METHODS

We evaluated plasma from 123 patients with COVID-19 to measure auto-abs to type I IFNs. We performed single-cell RNA sequencing (scRNA-seq) of peripheral blood mononuclear cells from the patients with auto-abs and conducted epitope mapping of the auto-abs.

RESULTS

Three of 19 severe and 4 of 42 critical COVID-19 patients had neutralizing auto-abs to type I IFNs. Patients with auto-abs to type I IFNs showed no characteristic clinical features. scRNA-seq from 38 patients with COVID-19 revealed that IFN signaling in conventional dendritic cells and canonical monocytes was attenuated, and SARS-CoV-2-specific BCR repertoires were decreased in patients with auto-abs. Furthermore, auto-abs to IFN-α2 from COVID-19 patients with auto-abs recognized characteristic epitopes of IFN-α2, which binds to the receptor.

CONCLUSION

Auto-abs to type I IFN found in COVID-19 patients inhibited IFN signaling in dendritic cells and monocytes by blocking the binding of type I IFN to its receptor. The failure to properly induce production of an antibody to SARS-CoV-2 may be a causative factor of COVID-19 severity.

ACC1-mediated fatty acid biosynthesis intrinsically controls thymic iNKT cell development

To meet the energetic requirements associated with activation, proliferation, and survival, T cells switch their metabolic signatures from energetically quiescent to activated. However, little is known about the role of metabolic pathway controlling the development of invariant natural killer T (iNKT) cells. In the present study, we found that acetyl-CoA carboxylase 1 (ACC1), a rate-limiting enzyme for the fatty acid biosynthesis pathway, plays an essential role in the development of iNKT cells in the thymus. Mice lacking T-cell specific ACC1 showed a reduced number of iNKT cells with an increased proportion of iNKT cells at immature stages 0 and 1. Furthermore, mixed bone marrow (BM) chimera experiments revealed that T-cell intrinsic ACC1 expression was selectively important for the development of thymic iNKT cells, especially for the differentiation of the NKT1 cell subset. Our single-cell RNA-sequencing (scRNA-seq) data and functional analysis demonstrated that ACC1 is responsible for survival of developing iNKT cells. Thus, these findings highlighted a novel role of ACC1 in controlling thymic iNKT cell development mediated by the control of cell survival.

CD69 imposes tumor-specific CD8+ T-cell fate in tumor-draining lymph nodes

Tumor-specific CD8+ T cells play a pivotal role in anti-tumor immunity and are a key target of immunotherapeutic approaches. Intratumoral CD8+ T cells are heterogeneous; Tcf1+ stem-like CD8+ T cells give rise to their cytotoxic progeny - Tim-3+ terminally differentiated CD8+ T cells. However, where and how this differentiation process occurs has not been elucidated. We herein show that terminally differentiated CD8+ T cells can be generated within tumor-draining lymph nodes (TDLNs) and that CD69 expression on tumor-specific CD8+ T cells controls its differentiation process through regulating the expression of the transcription factor TOX. In TDLNs, CD69 deficiency diminished TOX expression in tumor-specific CD8+ T cells, and consequently promoted generation of functional terminally differentiated CD8+ T cells. Anti-CD69 administration promoted the generation of terminally differentiated CD8+ T cells, and the combined use of anti-CD69 and anti-PD-1 showed an efficient anti-tumor effect. Thus, CD69 is an attractive target for cancer immunotherapy that synergizes with immune checkpoint blockade.

Pathogenic helper T cells as the novel therapeutic targets for immune-mediated intractable diseases

Allergic diseases arise from a complex interplay between immune system and environmental factors. A link between the pathogenesis of allergic diseases and type 2 immune responses has become evident, with conventional and pathogenic type 2 helper T (Th2) cells involved in both. Recently, there has been a significant development in therapeutic agents for allergic diseases: IL-5 and IL-5 receptor antagonists, Janus kinase (JAK) inhibitors, and sublingual immunotherapy (SLIT). Mepolizumab, an IL-5, and Benralizumab, an IL-5 receptor antagonist, modulate eosinophilic inflammation mediated by IL-5-producing Th2 cells. Delgocitinib shows that JAK-associated signaling is essential for the inflammatory reaction in atopic dermatitis, one of the common allergic diseases. SLIT has a significant effect on allergic rhinitis by reducing pathogenic Th2 cell numbers. More recently, novel molecules that are involved in pathogenic Th2 cell-mediated allergic diseases have been identified. These include calcitonin gene-related peptide (CGRP), reactive oxygen species (ROS) scavenging machinery regulated by the Txnip-Nrf2-Blvrb axis, and myosin light chain 9 (Myl9), which interacts with CD69. This review provides an updated view of the recent research on treatment of allergic diseases and their cause: conventional and pathogenic Th2 cells.

Increased Myosin light chain 9 expression during Kawasaki disease vasculitis

Introduction

Kawasaki disease (KD) is an acute systemic vasculitis that predominantly afflicts children. KD development is known to be associated with an aberrant immune response and abnormal platelet activation, however its etiology is still largely unknown. Myosin light chain 9 (Myl9) is known to regulate cellular contractility of both non-muscle and smooth muscle cells, and can be released from platelets, whereas any relations of Myl9 expression to KD vasculitis have not been examined.

Methods

Plasma Myl9 concentrations in KD patients and children with febrile illness were measured and associated with KD clinical course and prognosis. Myl9 release from platelets in KD patients was also evaluated in vitro. Myl9 expression was determined in coronary arteries from Lactobacillus casei cell wall extract (LCWE)-injected mice that develop experimental KD vasculitis, as well as in cardiac tissues obtained at autopsy from KD patients.

Results and discussion

Plasma Myl9 levels were significantly higher in KD patients during the acute phase compared with healthy controls or patients with other febrile illnesses, declined following IVIG therapy in IVIG-responders but not in non-responders. In vitro, platelets from KD patients released Myl9 independently of thrombin stimulation. In the LCWE-injected mice, Myl9 was detected in cardiac tissue at an early stage before inflammatory cell infiltration was observed. In tissues obtained at autopsy from KD patients, the highest Myl9 expression was observed in thrombi during the acute phase and in the intima and adventitia of coronary arteries during the chronic phase. Thus, our studies show that Myl9 expression is significantly increased during KD vasculitis and that Myl9 levels may be a useful biomarker to estimate inflammation and IVIG responsiveness to KD.

The cellular and molecular basis of CD69 function in anti-tumor immunity

Cancer immunotherapy utilizes our immune system to attack cancer cells and is an extremely promising strategy for cancer treatment. Although immune-checkpoint blockade, such as anti-PD-1 antibody (Ab), has demonstrated significant enhancement of anti-tumor immunity and has induced notable clinical outcomes, its response rates remain low, and adverse effects are always a matter of concern; therefore, new targets for cancer immunotherapy are always desired. In this situation, new concepts are needed to fuel the investigation of new target molecules for cancer immunotherapy. We propose that CD69 is one such target molecule. CD69 is known to be an activation marker of leukocytes and is also considered a crucial regulator of various immune responses through its interacting proteins. CD69 promotes T cell retention in lymphoid tissues via sphingosine-1-phosphate receptor 1 (S1P1) internalization and also plays roles in the pathogenesis of inflammatory disorders through interacting with its functional ligands Myl9/12 (myosin light chains 9, 12a and 12b). In anti-tumor immunity, CD69 is known to be expressed on T cells in the tumor microenvironment (TME) and tumor-draining lymph nodes (TDLNs). We revealed that CD69 negatively regulates the effector function of intratumoral T cells and importantly controls the 'exhaustion' of CD8 T cells. In addition, we and others showed that either CD69 deficiency or the administration of anti-CD69 monoclonal antibody enhances anti-tumor immunity. Thus, CD69 is an attractive target for cancer immunotherapy.

IFNγ suppresses the expression of GFI1 and thereby inhibits Th2 cell proliferation

While IFNγ is a well-known cytokine that actively promotes the type I immune response, it is also known to suppress the type II response by inhibiting the differentiation and proliferation of Th2 cells. However, the mechanism by which IFNγ suppresses Th2 cell proliferation is still not fully understood. We found that IFNγ decreases the expression of growth factor independent-1 transcriptional repressor (GFI1) in Th2 cells, resulting in the inhibition of Th2 cell proliferation. The deletion of the Gfi1 gene in Th2 cells results in the failure of their proliferation, accompanied by an impaired cell cycle progression. In contrast, the enforced expression of GFI1 restores the defective Th2 cell proliferation, even in the presence of IFNγ. These results demonstrate that GFI1 is a key molecule in the IFNγ-mediated inhibition of Th2 cell proliferation.

CD4 + T cells in inflammatory diseases : pathogenic T-helper cells and the CD69-Myl9 system

CD4 + T cells direct immune responses against infectious microorganisms but are also involved in the pathogenesis of inflammatory diseases. In the last two to three decades, various researchers have identified and characterized several functional CD4 + T cell subsets, including T-helper 1 (Th1), Th2, Th9 and Th17 cells and regulatory T (Treg) cells. In this mini-review, we introduce the concept of pathogenic Th cells that induce inflammatory diseases with a model of disease induction by a population of pathogenic Th cells; "pathogenic Th population disease-induction model". We will focus on Th2 cells that induce allergic airway inflammation-pathogenic Th2 cells (Tpath2 cells)-and discuss the nature of Tpath2 cells that shape the pathology of chronic inflammatory diseases. Various Tpath2 cell subsets have been identified and their unique features are summarized in mouse and human systems. Second, we will discuss how Th cells migrate and are maintained in chronic inflammatory lesions. We propose a model known as the "CD69-Myl9 system". CD69 is a cell surface molecule expressed on activated T cells and interaction with its ligand myosin light chain 9 (Myl9) is required for the induction of inflammatory diseases. Myl9 molecules in the small vessels of inflamed lungs may play a crucial role in the migration of activated T cells into inflammatory lesions. Emerging evidence may provide new insight into the pathogenesis of chronic inflammatory diseases and contribute to the development of new therapeutic strategies for intractable inflammatory disorders.

Myosin Light Chain 9/12 Regulates the Pathogenesis of Inflammatory Bowel Disease

The numbers of patients with inflammatory bowel disease (IBD), such as ulcerative colitis (UC) and Crohn’s disease (CD), have been increasing over time, worldwide; however, the pathogenesis of IBD is multifactorial and has not been fully understood. Myosin light chain 9 and 12a and 12b (Myl9/12) are known as ligands of the CD69 molecule. They create “Myl9 nets” that are often detected in inflamed site, which play a crucial role in regulating the recruitment and retention of CD69-expressing effector cells in inflamed tissues. We demonstrated the strong expression of Myl9/12 in the inflamed gut of IBD patients and mice with DSS-induced colitis. The administration of anti-Myl9/12 Ab to mice with DSS-induced colitis ameliorated the inflammation and prolonged their survival. The plasma Myl9 levels in the patients with active UC and CD were significantly higher than those in patients with disease remission, and may depict the disease severity of IBD patients, especially those with UC. Thus, our results indicate that Myl9/12 are involved in the pathogenesis of IBD, and are likely to be a new therapeutic target for patients suffering from IBD.

Essential Role for CD30-Transglutaminase 2 Axis in Memory Th1 and Th17 Cell Generation

Memory helper T (Th) cells are crucial for secondary immune responses against infectious microorganisms but also drive the pathogenesis of chronic inflammatory diseases. Therefore, it is of fundamental importance to understand how memory T cells are generated. However, the molecular mechanisms governing memory Th cell generation remain incompletely understood. Here, we identified CD30 as a molecule heterogeneously expressed on effector Th1 and Th17 cells, and CD30^hi effector Th1 and Th17 cells preferentially generated memory Th1 and Th17 cells. We found that CD30 mediated signal induced Transglutaminase-2 (TG2) expression, and that the TG2 expression in effector Th cells is essential for memory Th cell generation. In fact, Cd30-deficiency resulted in the impaired generation of memory Th1 and Th17 cells, which can be rescued by overexpression of TG2. Furthermore, transglutaminase-2 (Tgm2)-deficient CD4 T cells failed to become memory Th cells. As a result, T cells from Tgm2-deficient mice displayed impaired antigen-specific antibody production and attenuated Th17-mediated allergic responses. Our data indicate that CD30-induced TG2 expression in effector Th cells is essential for the generation of memory Th1 and Th17 cells, and that CD30 can be a marker for precursors of memory Th1 and Th17 cells.

Activated invariant natural killer T cells directly recognize leukemia cells in a CD1d-independent manner

Invariant natural killer T (iNKT) cells are innate‐like CD1d‐restricted T cells that express the invariant T cell receptor (TCR) composed of Vα24 and Vβ11 in humans. iNKT cells specifically recognize glycolipid antigens such as α‐galactosylceramide (αGalCer) presented by CD1d. iNKT cells show direct cytotoxicity toward CD1d‐positive tumor cells, especially when CD1d presents glycolipid antigens. However, iNKT cell recognition of CD1d‐negative tumor cells is unknown, and direct cytotoxicity of iNKT cells toward CD1d‐negative tumor cells remains controversial. Here, we demonstrate that activated iNKT cells recognize leukemia cells in a CD1d‐independent manner, however still in a TCR‐mediated way. iNKT cells degranulated and released Th1 cytokines toward CD1d‐negative leukemia cells (K562, HL‐60, REH) as well as αGalCer‐loaded CD1d‐positive Jurkat cells. The CD1d‐independent cytotoxicity was enhanced by natural killer cell‐activating receptors such as NKG2D, 2B4, DNAM‐1, LFA‐1 and CD2, but iNKT cells did not depend on these receptors for the recognition of CD1d‐negative leukemia cells. In contrast, TCR was essential for CD1d‐independent recognition and cytotoxicity. iNKT cells degranulated toward patient‐derived leukemia cells independently of CD1d expression. iNKT cells targeted myeloid malignancies more than acute lymphoblastic leukemia. These findings reveal a novel anti–tumor mechanism of iNKT cells in targeting CD1d‐negative tumor cells and indicate the potential of iNKT cells for clinical application to treat leukemia independently of CD1d.

Pathogenic Th17 cell differentiation is negatively regulated by let-7 microRNAs in a mouse model of multiple sclerosis

Autoimmune disorders such as multiple sclerosis (MS) are caused by proinflammatory events mediated by pathogenic Th17 cells. In MS, these cells arise in response to autoantigen recognition and exposure to the cytokines IL-1β and IL-23, migrate to the central nervous system (CNS) by following gradients of CCR2- and CCR5-cognate chemokines, and secrete GM-CSF. GM-CSF is essential for disease development, as it promotes the activation, differentiation, and recruitment of peripheral inflammatory myeloid cells to the CNS that directly demyelinate neurons and damage axons. Th17 cell pathogenicity in MS has been correlated with microRNA (miRNA) dysregulation, which leads to aberrant post-transcriptional regulation of gene expression and enhanced autoreactive phenotype. We found that the lethal-7 (let-7) miRNA family is abundantly expressed in naive CD4+ T cells, but gets dramatically downregulated over time following antigen encounter, indicating that let-7 may control the differentiation of pathogenic Th17 cells. To investigate a potential regulatory role for let-7 in Th17 cell autoreactivity, we used experimental autoimmune encephalomyelitis (EAE), the animal model of MS. Specifically, we demonstrated that let-7 confers protection from EAE by negatively regulating the proliferation, IL-1β/IL-23-dependent differentiation, and CCR2/CCR5-dependent migration of pathogenic Th17 cells to the CNS. Conversely, absence of let-7 led to enhanced Th17 cell autoreactivity and aggravated disease. Therefore, our results identify a novel regulatory role for let-7 miRNAs in pathogenic Th17 differentiation during EAE development, suggesting a promising therapeutic application for the treatment of MS-related autoimmune diseases.

Differentiation of Pathogenic Th17 Cells Is Negatively Regulated by Let-7 MicroRNAs in a Mouse Model of Multiple Sclerosis

Multiple sclerosis (MS) is a disabling demyelinating autoimmune disorder of the central nervous system (CNS) which is driven by IL-23- and IL-1β-induced autoreactive Th17 cells that traffic to the CNS and secrete proinflammatory cytokines. Th17 pathogenicity in MS has been correlated with the dysregulation of microRNA (miRNA) expression, and specific miRNAs have been shown to promote the pathogenic Th17 phenotype. In the present study, we demonstrate, using the animal model of MS, experimental autoimmune encephalomyelitis (EAE), that let-7 miRNAs confer protection against EAE by negatively regulating the proliferation, differentiation and chemokine-mediated migration of pathogenic Th17 cells to the CNS. Specifically, we found that let-7 miRNAs may directly target the cytokine receptors Il1r1 and Il23r, as well as the chemokine receptors Ccr2 and Ccr5. Therefore, our results identify a novel regulatory role for let-7 miRNAs in pathogenic Th17 differentiation during EAE development, suggesting a promising therapeutic application for disease treatment.

Crucial role of CD69 in anti-tumor immunity through regulating the exhaustion of tumor-infiltrating T cells

The introduction of immune checkpoint inhibitors in cancer treatment highlights the negative regulation of anti-tumor immunity, such as effector T-cell exhaustion in the tumor microenvironment. However, the mechanisms underlying the induction and prevention of T-cell exhaustion remain largely unknown. We found that CD69, a type II glycoprotein known to regulate inflammation through T-cell migration and retention in tissues, plays an important role in inducing the exhaustion of tumor-infiltrating T cells. Cd69-/- mice showed reduced tumor growth and metastasis in a 4T1-luc2 murine breast cancer model, in which increased numbers of tumor-infiltrating lymphocytes, relatively little T-cell exhaustion, and enhanced IFNγ production were observed. Anti-CD69 monoclonal antibody treatment attenuated the T-cell exhaustion and tumor progression in tumor-bearing mice. These findings highlight a novel role of CD69 in controlling the tumor immune escape mediated by T-cell exhaustion and indicate that CD69 is a novel target for cancer immunotherapy.

Survival of Naïve T Cells Requires the Expression of Let-7 miRNAs

Maintaining the diversity and constant numbers of naïve T cells throughout the organism's lifetime is necessary for efficient immune responses. Naïve T cell homeostasis, which consists of prolonged survival, occasional proliferation and enforcement of quiescence, is tightly regulated by multiple signaling pathways which are in turn controlled by various transcription factors. However, full understanding of the molecular mechanisms underlying the maintenance of the peripheral T cell pool has not been achieved. In the present study, we demonstrate that T cell-specific deficiency in let-7 miRNAs results in peripheral T cell lymphopenia resembling that of Dicer1 knockout mice. Deletion of let-7 leads to profound T cell apoptosis while overexpression prevents it. We further show that in the absence of let-7, T cells cannot sustain optimal levels of the pro-survival factor Bcl2 in spite of the intact IL-7 signaling, and re-expression of Bcl2 in let-7 deficient T cells completely rescues the survival defect. Thus, we have uncovered a novel let-7-dependent mechanism of post-transcriptional regulation of naïve T cell survival in vivo.

A new therapeutic target: the CD69-Myl9 system in immune responses

CD69 is an activation marker on leukocytes. Early studies showed that the CD69⁺ cells were detected in the lung of patients with asthmatic and eosinophilic pneumonia, suggesting that CD69 might play crucial roles in the pathogenesis of such inflammatory diseases, rather than simply being an activation marker. Intensive studies using mouse models have since clarified that CD69 is a functional molecule regulating the immune responses. We discovered that Myosin light chain 9, 12a, 12b (Myl9/12) are ligands for CD69 and that platelet-derived Myl9 forms a net-like structure (Myl9 nets) that is strongly detected inside blood vessels in inflamed lung. CD69-expressing activated T cells attached to the Myl9 nets can thereby migrate into the inflamed tissues through a system known as the CD69-Myl9 system. In this review, we summarize the discovery of the CD69-Myl9 system and discuss how this system is important in inflammatory immune responses. In addition, we discuss our recent finding that CD69 controls the exhaustion status of tumor-infiltrating T cells and that the blockade of the CD69 function enhances anti-tumor immunity. Finally, we discuss the possibility of CD69 as a new therapeutic target for patients with intractable inflammatory disorders and tumors.

CD69 prevents PLZFhi innate precursors from prematurely exiting the thymus and aborting NKT2 cell differentiation

While CD69 may regulate thymocyte egress by inhibiting S1P₁ expression, CD69 expression is not thought to be required for normal thymocyte development. Here we show that CD69 is in fact specifically required for the differentiation of mature NKT2 cells, which do not themselves express CD69. Mechanistically, CD69 expression is required on CD24⁺ PLZF^hi innate precursors for their retention in the thymus and completion of their differentiation into mature NKT2 cells. By contrast, CD69-deficient CD24⁺ PLZF^hi innate precursors express S1P₁ and prematurely exit the thymus, while S1P₁ inhibitor treatment of CD69-deficient mice retains CD24⁺ PLZF^hi innate precursors in the thymus and restores NKT2 cell differentiation. Thus, CD69 prevents S1P₁ expression on CD24⁺ PLZF^hi innate precursor cells from aborting NKT2 differentiation in the thymus. This study reveals the importance of CD69 to prolong the thymic residency time of developing immature precursors for proper differentiation of a T cell subset.

CD69 competes with S1P₁, a chemokine receptor mediating thymocyte egress, for surface expression on thymocytes, but whether CD69 is required for normal thymic development is unclear. Here the authors show that CD69 and S1P₁ synergize to control type 2 natural killer (NKT2) cells differentiation by modulating the thymic egress of NKT2 precursor.

Crucial role for CD69 in allergic inflammatory responses: CD69-Myl9 system in the pathogenesis of airway inflammation

CD69 has been known as an early activation marker of lymphocytes; whereas, recent studies demonstrate that CD69 also has critical functions in immune responses. Early studies using human samples revealed the involvement of CD69 in various inflammatory diseases including asthma. Moreover, murine disease models using Cd69^-/- mice and/or anti-CD69 antibody (Ab) treatment have revealed crucial roles for CD69 in inflammatory responses. However, it had not been clear how the CD69 molecule contributes to the pathogenesis of inflammatory diseases. We recently elucidated a novel mechanism, in which the interaction between CD69 and its ligands, myosin light chain 9, 12a and 12b (Myl9/12) play a critical role in the recruitment of activated T cells into the inflammatory lung. In this review, we first summarize CD69 function based on its structure and then introduce the evidence for the involvement of CD69 in human diseases and murine disease models. Then, we will describe how we discovered CD69 ligands, Myl9 and Myl12, and how the CD69-Myl9 system regulates airway inflammation. Finally, we will discuss possible therapeutic usages of the blocking Ab to the CD69-Myl9 system.

Timing and duration of MHC I positive selection signals are adjusted in the thymus to prevent lineage errors

Major histocompatibility complex class I (MHC I) positive selection of CD8⁺ T cells in the thymus requires that T cell antigen receptor (TCR) signaling end in time for cytokines to induce Runx3d, the CD8-lineage transcription factor. We examined the time required for these events and found that the overall duration of positive selection was similar for all CD8⁺ thymocytes in mice, despite markedly different TCR signaling times. Notably, prolonged TCR signaling times were counter-balanced by accelerated Runx3d induction by cytokines and accelerated differentiation into CD8⁺ T cells. Consequently, lineage errors did not occur except when MHC I-TCR signaling was so prolonged that the CD4-lineage-specifying transcription factor ThPOK was expressed, preventing Runx3d induction. Thus, our results identify a compensatory signaling mechanism that prevents lineage-fate errors by dynamically modulating Runx3d induction rates during MHC I positive selection.

Myosin light chains 9 and 12 are functional ligands for CD69 that regulate airway inflammation

Recent decades have witnessed a rapid worldwide increase in chronic inflammatory disorders such as asthma. CD4⁺ T helper 2 cells play critical roles in the pathogenesis of allergic airway inflammation, and CD69 expression on activated CD4 T cells is required to induce allergic inflammation in tissues. However, how CD69 mechanistically controls allergic inflammation remains poorly defined. In lymphoid tissues, CD69 regulates cellular retention through inhibition of S1P1 expression and requires no specific ligands to function. In contrast, we show herein that myosin light chain (Myl) 9 and Myl12 are new functional ligands for CD69. Blockade of CD69-Myl9/12 interaction ameliorates allergic airway inflammation in ovalbumin-induced and house dust mite-induced mouse models of asthma. Within the inflamed mouse airways, we found that the expression of Myl9/12 was increased and that platelet-derived Myl9/12 localized to the luminal surface of blood vessels and formed intravascular net-like structures. Analysis of nasal polyps of eosinophilic chronic rhinosinusitis patients revealed that Myl9/12 expression was increased in inflammatory lesions and was distributed within net-like structures in the intravascular space. In addition, we detected Myl9/12 in perivascular spaces where many CD69⁺ cells were positioned within Myl9/12 structures. Thus, CD69-Myl9/12 interaction is a key event in the recruitment of activated CD69⁺ T cells to inflamed tissues and could be a therapeutic target for intractable airway inflammatory diseases.

Methylation of Gata3 protein at Arg-261 regulates transactivation of the Il5 gene in T helper 2 cells

Gata3 acts as a master regulator for T helper 2 (Th2) cell differentiation by inducing chromatin remodeling of the Th2 cytokine loci, accelerating Th2 cell proliferation, and repressing Th1 cell differentiation. Gata3 also directly transactivates the interleukin-5 (Il5) gene via additional mechanisms that have not been fully elucidated. We herein identified a mechanism whereby the methylation of Gata3 at Arg-261 regulates the transcriptional activation of the Il5 gene in Th2 cells. Although the methylation-mimicking Gata3 mutant retained the ability to induce IL-4 and repress IFNγ production, the IL-5 production was selectively impaired. We also demonstrated that heat shock protein (Hsp) 60 strongly associates with the methylation-mimicking Gata3 mutant and negatively regulates elongation of the Il5 transcript by RNA polymerase II. Thus, arginine methylation appears to play a pivotal role in the organization of Gata3 complexes and the target gene specificity of Gata3.

Lck availability during thymic selection determines the recognition specificity of the T cell repertoire

Thymic selection requires signaling by the protein tyrosine kinase Lck to generate T cells expressing αβ T cell antigen receptors (TCR). For reasons not understood, the thymus selects only αβTCR that are restricted by major histocompatibility complex (MHC)-encoded determinants. Here, we report that Lck proteins that were coreceptor associated promoted thymic selection of conventionally MHC-restricted TCR, but Lck proteins that were coreceptor free promoted thymic selection of MHC-independent TCR. Transgenic TCR with MHC-independent specificity for CD155 utilized coreceptor-free Lck to signal thymic selection in the absence of MHC, unlike any transgenic TCR previously described. Thus, the thymus can select either MHC-restricted or MHC-independent αβTCR depending on whether Lck is coreceptor associated or coreceptor free. We conclude that the intracellular state of Lck determines the specificity of thymic selection and that Lck association with coreceptor proteins during thymic selection is the mechanism by which MHC restriction is imposed on a randomly generated αβTCR repertoire.

IL-7 signaling must be intermittent, not continuous, during CD8⁺ T cell homeostasis to promote cell survival instead of cell death

The maintenance of naive CD8(+) T cells is necessary for lifelong immunocompetence but for unknown reasons requires signaling via both interleukin 7 (IL-7) and the T cell antigen receptor (TCR). We now report that naive CD8(+) T cells required IL-7 signaling to be intermittent, not continuous, because prolonged IL-7 signaling induced naive CD8(+) T cells to proliferate, produce interferon-γ (IFN-γ) and undergo IFN-γ-triggered cell death. Homeostatic engagement of the TCR interrupted IL-7 signaling and thereby supported the survival and quiescence of CD8(+) T cells. However, CD8(+) T cells with insufficient TCR affinity for self ligands received prolonged IL-7 signaling and died during homeostasis. In this study we identified regulation of the duration of IL-7 signaling by homeostatic engagement of the TCR as the basis for in vivo CD8(+) T cell homeostasis.

Polycomb group gene product Ring1B regulates Th2-driven airway inflammation through the inhibition of Bim-mediated apoptosis of effector Th2 cells in the lung

Polycomb group (PcG) gene products regulate the maintenance of homeobox gene expression in Drosophila and vertebrates. In the immune system, PcG molecules control cell cycle progression of thymocytes, Th2 cell differentiation, and the generation of memory CD4 T cells. In this paper, we extended the study of PcG molecules to the regulation of in vivo Th2 responses, especially allergic airway inflammation, by using conditional Ring1B-deficient mice with a CD4 T cell-specific deletion of the Ring1B gene (Ring1B(-/-) mice). In Ring1B(-/-) mice, CD4 T cell development appeared to be normal, whereas the differentiation of Th2 cells but not Th1 cells was moderately impaired. In an Ag-induced Th2-driven allergic airway inflammation model, eosinophilic inflammation was attenuated in Ring1B(-/-) mice. Interestingly, Ring1B(-/-) effector Th2 cells were highly susceptible to apoptosis in comparison with wild-type effector Th2 cells in vivo and in vitro. The in vitro experiments revealed that the expression of Bim was increased at both the transcriptional and protein levels in Ring1B(-/-) effector Th2 cells, and the enhanced apoptosis in Ring1B(-/-) Th2 cells was rescued by the knockdown of Bim but not the other proapoptotic genes, such as Perp, Noxa, or Bax. The enhanced apoptosis detected in the transferred Ring1B(-/-) Th2 cells in the lung of the recipient mice was also rescued by knockdown of Bim. Therefore, these results indicate that Ring1B plays an important role in Th2-driven allergic airway inflammation through the control of Bim-dependent apoptosis of effector Th2 cells in vivo.

Memory Th1/Th2 cell generation controlled by Schnurri-2

Schnurri (Shn) is a large zinc-finger containingprotein, which plays a critical role in cell growth, signal transduction and lymphocyte development. There are three orthologues (Shn-1, Shn-2 and Shn-3) in vertebrates. In Shn-2-deficient mice, the activation of NF-kappaB in CD4 T cells is upregulated and their ability to differentiate into Th2 cells is enhanced in part through the increased expression of GATA3. Shn-2 is found to compete with p50 NF-kappaB for binding to a consensus NF-kappaB motif and inhibit the NF-kappaB-driven promoter activity. In addition, Th2-driven allergic airway inflammation was enhanced in Shn-2-deficient mice. Therefore, Shn-2 appears to negatively control the differentiation of Th2 cells and Th2 responses through the repression of NF-kappaB function. Memory Th1/Th2 cells are not properly generated from Shn-2-deficient effector Th1/Th2 cells. The expression levels of CD69 and the number ofapoptotic cells are selectively increased in Shn-2-deficient Thl/Th2 cells when they are transferred into syngeneic host animals, in which memoryh Th1/Th2 cells are generated within a month. In addition, an increased susceptibility to apoptotic cell death is also observed in vitro accompanied with the increased expression of FasL, one of the NF-kappaB-dependent genes. Th2 effector cells overexpressing the p65 subunit of NF-kappaB demonstrate a decreased cell survival particularly in the lymph node. These results indicate that Shn-2-mediated repression of NF-kappaB is required for cell survival and the successful generation of memory Th1/Th2 cells. This may point to the possibility that after antigen clearance the recovery of the quiescent state in effector Th cells is required for the generation of memory Th cells. A repressor molecule Shn-2 plays an important role in this process.

Schnurri-2 controls memory Th1 and Th2 cell numbers in vivo

Schnurri-2 (Shn-2) is a large zinc-finger containing protein, and it plays a critical role in cell growth, signal transduction and lymphocyte development. In Shn-2-deficient CD4 T cells, the activation of NF-kappaB was up-regulated and their ability to differentiate into Th2 cells was enhanced. We herein demonstrate that Th1 and Th2 memory cells are not properly generated from Shn-2-deficient effector Th1/Th2 cells. Even a week after the transfer of effector Th1/Th2 cells into syngeneic mice, a dramatic decrease in the number of Shn-2-deficient donor T cells was detected particularly in the lymphoid organs. The transferred Shn-2-deficient Th1/Th2 cells express higher levels of the activation marker CD69. No significant defect in the BrdU incorporation in the Shn-2-deficient transferred CD4 T cells was observed. The numbers of apoptotic cells were selectively higher in Shn-2-deficient donor Th1/Th2 cell population. Moreover, Shn-2-deficient effector Th1 and Th2 cells showed an increased susceptibility to cell death in in vitro cultures with increased expression of FasL. Transfer of Th2 effector cells over-expressing the p65 subunit of NF-kappaB resulted in a decreased number of p65-expressing cells in the lymphoid organs. As expected, T cell-dependent Ab responses after in vivo immunization of Shn-2-deficient mice were significantly reduced. Thus, Shn-2 appears to control the generation of memory Th1/Th2 cells through a change in their susceptibility to cell death.

Schnurri-2 regulates Th2-dependent airway inflammation and airway hyperresponsiveness

Schnurri (Shn)-2 is a large zinc finger-containing protein, which plays a critical role in cell growth, signal transduction and lymphocyte development. In Shn-2-deficient (Shn-2(-/-)) CD4 T cells, the activation of nuclear factor-kappaB is up-regulated and their ability to differentiate into Th2 is enhanced. Here, we extend our investigation and demonstrate that Shn-2 regulates Th2 responses in vivo using an ovalbumin-induced allergic asthma model. Eosinophilic inflammation, mucus hyperproduction and airway hyperresponsiveness (AHR) were all enhanced in Shn-2(-/-) mice. Moreover, eosinophilic infiltration and AHR were enhanced in mice given a transfer of Shn-2(-/-) effector Th2. Shn-2 in Th2 is thus considered to play an important role as a negative regulator in allergic airway inflammation.

Shnurri-2 controls memory Th1 and Th2 cell numbers in vivo (84.3)

Schnurri-2 (Shn-2) is a large zinc-finger containing protein, and it plays a critical role in cell growth, signal transduction and lymphocyte development. In Shn-2-deficient CD4 T cells, the activation of NF-kB was upregulated and their ability to differentiate into Th2 cells was enhanced. We herein demonstrate that Th1 and Th2 memory cells are not properly generated from Shn-2-deficient effector Th1/Th2 cells. Even a week after the transfer of effector Th1/Th2 cells into syngeneic mice, a dramatic decrease in the number of Shn-2-deficient donor T cells was detected particularly in the lymphoid organs. The transferred Shn-2-deficient Th1/Th2 cells express higher levels of the activation marker CD69. No significant defect in the BrdU incorporation in the Shn-2-deficient transferred CD4 T cells was observed. The numbers of apoptotic cells were selectively higher in Shn-2-deficient donor Th1/Th2 cell population. Moreover, Shn-2-deficient effector Th1 and Th2 cells showed an increased susceptibility to cell death in in vitro cultures with increased expression of FasL. Transfer of Th2 effector cells over-expressing the p65 subunit of NF-kB resulted in a decreased number of p65-expressing cells in the lymphoid organs. As expected, T cell-dependent antibody responses after in vivo immunization of Shn-2-deficient mice were significantly reduced. Thus, Shn-2 appears to control the generation of memory Th1/Th2 cells through a change in their susceptibility to cell death.

Regulation of Th2 cell development by Polycomb group gene bmi-1 through the stabilization of GATA3

The Polycomb group (PcG) gene products regulate the maintenance of the homeobox gene expression in Drosophila and vertebrates and also the cell cycle progression in thymocytes and Th2 cell differentiation in mature T cells. We herein studied the role of PcG gene bmi-1 product in Th1/Th2 cell differentiation and found that Bmi-1 facilitates Th2 cell differentiation in a Ring finger-dependent manner. Biochemical studies indicate that Bmi-1 interacts with GATA3 in T cells, which is dependent on the Ring finger of Bmi-1. The overexpression of Bmi-1 resulted in a decreased ubiquitination and an increased protein stability of GATA3. In bmi-1-deficient Th cells, the levels of Th2 cell differentiation decreased as the degradation and ubiquitination on GATA3 increased. Therefore, Bmi-1 plays a crucial role in the control of Th2 cell differentiation in a Ring finger-dependent manner by regulating GATA3 protein stability.

Chromatin remodeling at the Th2 cytokine gene loci in human type 2 helper T cells

The differentiation of mouse naïve CD4 T cells into type 2 helper (Th2) cells is accompanied by chromatin remodeling at the nucleosomes associated with the IL-4, IL-13 and IL-5 genes. However, little is known about how chromatin remodeling of these Th2 cytokine gene loci occurs in human Th2 cells. We herein established an in vitro culture system in which both Th1 and Th2 cells are efficiently differentiated from human peripheral blood naïve CD4 T cells. This system allowed us to investigate the chromatin status at the Th2 cytokine gene loci and the IFNgamma locus in human Th2 and Th1 cells, respectively. In typical individuals, the chromatin remodeling indicated by the induction of hyper-acetylation of histone H3 lysine 9 and hyper-methylation of histone H3 lysine 4 was induced at the whole Th2 cytokine gene loci in developing Th2 cells. We more precisely assessed the methylation status of histone H3 lysine 4 at the Th2 cytokine gene loci (IL-5 exon 3, IL-5 promoter, IL-5/RAD50 intergenic region, RAD50 promoter, CGRE, CNS1, IL-13 promoter, IL-4 promoter, and VA enhancer regions) and the IFNgamma locus in developing Th1 and Th2 cells prepared from 20 healthy volunteers. Th2-cell specific chromatin remodeling was induced at most of the Th2 cytokine gene loci. In parallel with the induction of chromatin remodeling, GATA3 mRNA was preferentially expressed in developing Th2 cells, whereas T-bet, HLX and ROG mRNA was selectively expressed in developing Th1 cells.

Hyperresponsive TH2 cells with enhanced nuclear factor-κB activation induce atopic dermatitis–like skin lesions in Nishiki-nezumi Cinnamon/Nagoya mice

BACKGROUND

Nishiki-nezumi Cinnamon/Nagoya (NC/Nga) mice raised in nonair-controlled conventional circumstances spontaneously develop atopic dermatitis-like skin lesions; however, the underlying mechanisms remain unclear.

OBJECTIVE

We wanted to identify the critical intracellular signaling molecules in T cells that induce atopic dermatitis-like skin legions in NC/Nga mice.

METHODS

We examined the levels of signal transduction and cytokine production in T cells, particularly those in atopic dermatitis-like lesions induced by the topical injection of mite antigens in NC/Nga mice under specific pathogen-free conditions.

RESULTS

In NC/Nga mice maintained under specific pathogen-free conditions, the capability of T(H)1/T(H)2 and T cytotoxic 1/T cytotoxic 2 (Tc1/Tc2) cell differentiation increased significantly. T-cell antigen receptor-mediated activation of the extracellular signal-regulated kinase/mitogen-activated protein kinase cascade and nuclear factor-kappaB (NF-kappaB) signaling were enhanced in NC/Nga T cells. The expression of T(H)2 cytokines (IL-4, IL-13, and IL-5) and that of GATA-binding protein 3 (GATA3), avian musculoaponeurotic fibrosarcoma (c-Maf), NF-kappaB, and activator protein 1 (AP1) selectively increased in draining lymph node T cells of NC/Nga mice. Moreover, the cell transfer of inhibitory NF-kappaB mutant-infected T(H)2 cells reduced ear thickness in the mite antigen-induced skin lesion of NC/Nga mice.

CONCLUSION

Hyperresponsive T(H)2 cells with an enhanced activity of NF-kappaB and AP1 play a crucial role in the pathogenesis of atopic dermatitis-like skin lesions in NC/Nga mice.

CLINICAL IMPLICATIONS

These results indicate potential therapeutic usefulness of developing selective inhibitors for NF-kappaB in the treatment of human atopic dermatitis.

Crucial role of MLL for the maintenance of memory T helper type 2 cell responses

The Mixed-Lineage Leukemia (MLL) gene, a mammalian homolog of the Drosophila trithorax, is implicated in regulating the maintenance of Hox gene expression and hematopoiesis. The physiological functions of MLL in the immune system remain largely unknown. Although MLL(+/-) CD4 T cells differentiate normally into antigen-specific effector Th1/Th2 cells in vitro, the ability of memory Th2 cells to produce Th2 cytokines was selectively reduced. Furthermore, histone modifications at the Th2 cytokine gene loci were not properly maintained in MLL(+/-) memory Th2 cells. The reduced expression of MLL in memory Th2 cells resulted in decreased GATA3 expression accompanied with impaired GATA3 locus histone modifications. The direct association of MLL with the GATA3 locus and the Th2 cytokine gene loci was demonstrated. Memory Th2 cell-dependent allergic airway inflammation was decreased in MLL(+/-) Th2 cell-transferred mice. Thus, a crucial role for MLL in the maintenance of memory Th2 cell function is indicated.

Impaired GATA3-Dependent Chromatin Remodeling and Th2 Cell Differentiation Leading to Attenuated Allergic Airway Inflammation in Aging Mice

Age-related changes in lymphocytes are most prominent in the T cell compartment. There have been substantial numbers of reports on T cell function in aged mice and humans, such as on the production of Th1 and Th2 cytokines, but the results show considerable variation and contradictions. In the present study, we used 8- to 12-mo-old aging mice and a well-established in vitro Th1/Th2 cell differentiation culture system to identify molecular defects in Th1/Th2 cell differentiation that can be detected in the relatively early stages of aging. The capability to differentiate into Th2 cells is reduced in aging mouse CD4(+) T cells. Decreased activation of the ERK MAPK cascade upon TCR stimulation, but normal intracellular-free calcium ion concentration mobilization and normal IL-4-induced STAT6 activation were observed in aging mouse CD4(+) T cells. In addition, reduced expression of GATA3 was detected in developing Th2 cells. Chromatin remodeling of the Th2 cytokine gene locus was found to be impaired. Th2-dependent allergic airway inflammation was milder in aging mice compared with in young adult mice. These results suggest that the levels of Th2 cell differentiation and resulting Th2-dependent immune responses, including allergic airway inflammation, decline during aging through defects in the activation of the ERK MAPK cascade, expression of GATA3 protein and GATA3-dependent chromatin remodeling of the Th2 cytokine gene locus. In the present study, we provide the first evidence indicating that a chromatin-remodeling event in T cells is impaired by aging.

Regulation of T helper type 2 cell differentiation by murine Schnurri-2

Schnurri (Shn) is a large zinc finger protein implicated in cell growth, signal transduction, and lymphocyte development. Vertebrates possess at least three Shn orthologues (Shn-1, Shn-2, and Shn-3), which appear to act within the bone morphogenetic protein, transforming growth factor beta, and activin signaling pathways. However, the physiological functions of the Shn proteins remain largely unknown. In Shn-2-deficient mice, mature peripheral T cells exhibited normal anti-T cell receptor-induced proliferation, although there was dramatic enhancement in the differentiation into T helper type (Th)2 cells and a marginal effect on Th1 cell differentiation. Shn-2-deficient developing Th2 cells showed constitutive activation of nuclear factor kappaB (NF-kappaB) and enhanced GATA3 induction. Shn-2 was able to compete with p50 NF-kappaB for binding to a consensus NF-kappaB motif and inhibit NF-kappaB-driven promoter activity. Thus, Shn-2 plays a crucial role in the control of Th2 cell differentiation by regulating NF-kappaB function.

Differentiation of NK1 and NK2 Cells

Natural killer type-1 (NK1)/NK2 terminology was proposed as an analogy to T helper type-1 (Th1)/Th2 subsets of CD4 T cells. In addition to well recognized IFN-gamma-producing NK1 cells, recent accumulating evidence suggests the presence and the regulatory function of NK2 cells, which produce type-2 cytokines, such as IL-5 and IL-13. Most studies on the production of cytokines by NK1/NK2 subsets have been performed in the human system. Recently, a mouse in vitro NK1/NK2 cell differentiation system was established. A linear 2-0-1 model has been proposed for the differentiation of NK1/NK2 cell subsets, but the branching NK1/NK2 cell differentiation model, comparable to Thl/Th2 cell differentiation, remains a likely explanation. In this review, we summarize the evidence indicating the unique features of NK1/NK2 cells and discuss the above two NK cell differentiation models. In addition, we point to interesting similarities in the expression of transcription factors that regulate cytokine production in NK cells and CD8 T cells.