Accumulation of CD28null Senescent T-Cells Is Associated with Poorer Outcomes in COVID19 Patients.

Coronavirus disease 2019 (COVID-19), a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes infectious disease, and manifests in a wide range of symptoms from asymptomatic to severe illness and even death. Severity of infection is related to many risk factors, including aging and an array of underlying conditions, such as diabetes, hypertension, chronic obstructive pulmonary disease (COPD), and cancer. It remains poorly understood how these conditions influence the severity of COVID-19. Expansion of the CD28null senescent T-cell populations, a common phenomenon in aging and several chronic inflammatory conditions, is associated with higher morbidity and mortality rates in COVID-19. Here, we summarize the potential mechanisms whereby CD28null cells drive adverse outcomes in disease and predispose patients to devastating COVID-19, and discuss possible treatments for individuals with high counts of CD28null senescent T-cells.

RORα is critical for mTORC1 activity in T cell-mediated colitis.

Inflammatory bowel disease (IBD) is multi-factorial chronic intestinal inflammation driven by pathogenic T cells, among which a large portion of patients are resistant to current anti-inflammatory regimes. The mechanisms underlying colitis pathogenicity and drug resistance are not fully understood. Here, we demonstrate that RORα is highly expressed in active UC patients, particularly in those non-responsive to anti-TNF treatment. Rorα deficiency in CD4+ T cells greatly reduced colitis development. Mechanistically, RORα regulated T cell infiltration in colon and inhibited T cell apoptosis. Meanwhile, genome-wide occupancy and transcriptome analysis revealed that RORα promoted mTORC1 activation. mTORC1 signaling, also hyperactivated in active UC patients, is necessary for T cell-mediated colitis. Our results thus demonstrate a crucial role of the RORα-mTORC1 axis in CD4+ T cells in promoting IBD, which may be targeted in human patients.

Adipose mTORC1 Suppresses Prostaglandin Signaling and Beige Adipogenesis via the CRTC2-COX-2 Pathway.

Beige adipocytes are present in white adipose tissue (WAT) and have thermogenic capacity to orchestrate substantial energy metabolism and counteract obesity. However, adipocyte-derived signals that act on progenitor cells to control beige adipogenesis remain poorly defined. Here, we show that adipose-specific depletion of Raptor, a key component of mTORC1, promoted beige adipogenesis through prostaglandins (PGs) synthesized by cyclooxygenase-2 (COX-2). Moreover, Raptor-deficient mice were resistant to diet-induced obesity and COX-2 downregulation. Mechanistically, mTORC1 suppressed COX-2 by phosphorylation of CREB-regulated transcription coactivator 2 (CRTC2) and subsequent dissociation of CREB to cox-2 promoter in adipocytes. PG treatment stimulated PKA and promoted differentiation of progenitor cells to beige adipocytes in culture. Ultimately, we show that pharmacological inhibition or suppression of COX-2 attenuated mTORC1 inhibition-induced thermogenic gene expression in inguinal WAT in vivo and in vitro. Our study identifies adipocyte-derived PGs as key regulators of white adipocyte browning, which occurs through mTORC1 and CRTC2.

Orchestration of epithelial-derived cytokines and innate immune cells in allergic airway inflammation.

Allergic asthma, a chronic respiratory disease, is a leading worldwide health problem, which inflames and constricts the airways, leading to breathing difficulty. Many studies have focused on the pathogenesis contributed by the adaptive immune system, including CD4+ T lymphocytes in delayed type hypersensitivity and B cell-produced IgE in anaphylaxis. More recently, a focus on the airway mucosal barrier and the innate immune system has highlighted, in coordination with T and B cells, to initiate and establish disease. This review highlights the impacts of epithelial-derived cytokines and innate immune cells on allergic airway reactions.

Myeloid adrenergic signaling via CaMKII forms a feedforward loop of catecholamine biosynthesis.

Type 2 immune response has been shown to facilitate cold-induced thermogenesis and browning of white fat. However, whether alternatively activated macrophages produce catecholamine and substantially promote adaptive thermogenesis in adipose tissue remains controversial. Here, we show that tyrosine hydroxylase (TyrH), a rate-limiting enzyme of catecholamine biosynthesis, was expressed and phosphorylated in adipose-resident macrophages. In addition, the plasma level of adrenaline was increased by cold stress in mice, and treatment of macrophages with adrenaline stimulated phosphorylation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) and TyrH. Genetic and pharmacological inhibition of CaMKII or PKA signaling diminished adrenaline-induced phosphorylation of TyrH in primary macrophages. Consistently, overexpression of constitutively active CaMKII upregulated basal TyrH phosphorylation, while suppressing the stimulatory effect of adrenaline on TyrH in macrophages. Myeloid-specific disruption of CaMKIIγ suppressed both the cold-induced production of norepinephrine and adipose UCP1 expression in vivo and the stimulatory effect of adrenaline on macrophage-dependent activation of brown adipocytes in vitro. Lack of CaMKII signaling attenuated catecholamine production mediated by cytokines IL-4 and IL-13, key inducers of type 2 immune response in primary macrophages. Taken together, these results suggest a feedforward mechanism of adrenaline in adipose-resident macrophages, and that myeloid CaMKII signaling plays an important role in catecholamine production and subsequent beige fat activation.

CISH controls bacterial burden early after infection with Mycobacterium tuberculosis in mice.

CISH gene has been associated with increased susceptibility to human tuberculosis. We found that cish-/- mice had higher M. tuberculosis load in spleens and lungs up to 2.5 weeks after infection but not later compared to controls. Cish mRNA levels were increased in lungs at early and late time points after M. tuberculosis infection. In relation, the titers of inos and tnf mRNA in lungs were reduced early after infection of cish-/- mice. The transfer of cish-/- and control T cells conferred rag1-/- mice similar protection to infection with M. tuberculosis. Macrophages showed increased cish mRNA levels after M. tuberculosis infection in vitro. However, mycobacterial uptake and growth in cish-/- and control macrophages was similar. Thus, we here show that CISH mediates control of M. tuberculosis in mice early after infection via regulation of innate immune mechanisms.

A protective role by interleukin-17F in colon tumorigenesis.

Interleukin-17F (IL-17F), produced by Th17 cells and other immune cells, is a member of IL-17 cytokine family with highest homology to IL-17A. IL-17F has been shown to have multiple functions in inflammatory responses. While IL-17A plays important roles in cancer development, the function of IL-17F in tumorigenesis has not yet been elucidated. In the current study, we found that IL-17F is expressed in normal human colonic epithelial cells, but this expression is greatly decreased in colon cancer tissues. To examine the roles of IL-17F in colon cancer, we have used IL-17F over-expressing colon cancer cell lines and IL-17F-deficient mice. Our data showed decreased tumor growth of IL-17F-transfected HCT116 cells comparing to mock transfectants when transplanted in nude mice. Conversely, there were increased colonic tumor numbers and tumor areas in Il-17f(-/-) mice than those from wild-type controls after colon cancer induction. These results indicate that IL-17F plays an inhibitory role in colon tumorigenesis in vivo. In IL-17F over-expressing tumors, there was no significant change in leukocyte infiltration; instead, we found decreased VEGF levels and CD31(+) cells. While the VEGF levels were increased in the colon tissues of Il-17f(-/-) mice with colon cancer. Together, our findings demonstrate a protective role for IL-17F in colon cancer development, possibly via inhibiting tumor angiogenesis.

Requirement for the basic helix-loop-helix transcription factor Dec2 in initial TH2 lineage commitment.

How naive CD4(+) T cells commit to the T helper type 2 (T(H)2) lineage is poorly understood. Here we show that the basic helix-loop-helix transcription factor Dec2 was selectively expressed in T(H)2 cells. CD4(+) T cells from Dec2-deficient mice showed defective T(H)2 differentiation in vitro and in vivo in an asthma model and in response to challenge with a parasite antigen. Dec2 promoted expression of interleukin 4 (IL-4), IL-5 and IL-13 during early T(H)2 differentiation and directly bound to and activated transcription of genes encoding the transcription factors JunB and GATA-3. As GATA-3 induces Dec2 expression, our findings also indicate a feed-forward regulatory circuit during T(H)2 differentiation.

T helper 17 cells promote cytotoxic T cell activation in tumor immunity.

Although T helper 17 (Th17) cells have been found in tumor tissues, their function in cancer immunity is unclear. We found that interleukin-17A (IL-17A)-deficient mice were more susceptible to developing lung melanoma. Conversely, adoptive T cell therapy with tumor-specific Th17 cells prevented tumor development. Importantly, the Th17 cells retained their cytokine signature and exhibited stronger therapeutic efficacy than Th1 cells. Unexpectedly, therapy using Th17 cells elicited a remarkable activation of tumor-specific CD8(+) T cells, which were necessary for the antitumor effect. Th17 cells promoted dendritic cell recruitment into the tumor tissues and in draining lymph nodes increased CD8 alpha(+) dendritic cells containing tumor material. Moreover, Th17 cells promoted CCL20 chemokine production by tumor tissues, and tumor-bearing CCR6-deficient mice did not respond to Th17 cell therapy. Thus, Th17 cells elicited a protective inflammation that promotes the activation of tumor-specific CD8(+) T cells. These findings have important implications in antitumor immunotherapies.

Bcl6 mediates the development of T follicular helper cells.

A fundamental function of CD4+ helper T (T(H)) cells is the regulation of B cell-mediated humoral immunity. Development of T follicular helper (T(FH)) cells that provide help to B cells is mediated by the cytokines interleukin-6 and interleukin-21 but is independent of TH1, TH2, and TH17 effector cell lineages. Here, we characterize the function of Bcl6, a transcription factor selectively expressed in T(FH) cells. Bcl6 expression is regulated by interleukin-6 and interleukin-21. Bcl6 overexpression induced T(FH)-related gene expression and inhibited other T(H) lineage cell differentiation in a DNA binding-dependent manner. Moreover, Bcl6 deficiency in T cells resulted in impaired T(FH) cell development and germinal center reactions, and altered production of other effector T cell subsets. Our data thus illustrate that Bcl6 is required for programming of T(FH) cell generation.

Regulation and function of proinflammatory TH17 cells.

Naïve CD4(+) helper T (TH) cells, upon activation by antigen-presenting cells (APC), differentiate into different types of effector cells that are characterized by their distinct cytokine production profiles and immune regulatory functions. In addition to TH1 and TH2 cells, a third subset of effector TH cells has recently been described and termed TH17. Since their identification, TH17 cells have emerged as crucial players in infectious, inflammatory, and autoimmune diseases, and cancer. In this review, we summarize the latest discoveries on the cytokine-mediated regulation and transcriptional programming of TH17 cells and their roles in different immune responses and diseases.

Generation of T follicular helper cells is mediated by interleukin-21 but independent of T helper 1, 2, or 17 cell lineages.

After activation, CD4(+) helper T (Th) cells differentiate into distinct effector subsets. Although chemokine (C-X-C motif) receptor 5-expressing T follicular helper (Tfh) cells are important in humoral immunity, their developmental regulation is unclear. Here we show that Tfh cells had a distinct gene expression profile and developed in vivo independently of the Th1 or Th2 cell lineages. Tfh cell generation was regulated by ICOS ligand (ICOSL) expressed on B cells and was dependent on interleukin-21 (IL-21), IL-6, and signal transducer and activator of transcription 3 (STAT3). However, unlike Th17 cells, differentiation of Tfh cells did not require transforming growth factor beta (TGF-beta) or Th17-specific orphan nuclear receptors RORalpha and RORgamma in vivo. Finally, naive T cells activated in vitro in the presence of IL-21 but not TGF-beta signaling preferentially acquired Tfh gene expression and promoted germinal-center reactions in vivo. This study thus demonstrates that Tfh is a distinct Th cell lineage.

Regulation of inflammatory responses by IL-17F.

Although interleukin (IL) 17 has been extensively characterized, the function of IL-17F, which has an expression pattern regulated similarly to IL-17, is poorly understood. We show that like IL-17, IL-17F regulates proinflammatory gene expression in vitro, and this requires IL-17 receptor A, tumor necrosis factor receptor-associated factor 6, and Act1. In vivo, overexpression of IL-17F in lung epithelium led to infiltration of lymphocytes and macrophages and mucus hyperplasia, similar to observations made in IL-17 transgenic mice. To further understand the function of IL-17F, we generated and analyzed mice deficient in IL-17F or IL-17. IL-17, but not IL-17F, was required for the initiation of experimental autoimmune encephalomyelitis. Mice deficient in IL-17F, but not IL-17, had defective airway neutrophilia in response to allergen challenge. Moreover, in an asthma model, although IL-17 deficiency reduced T helper type 2 responses, IL-17F-deficient mice displayed enhanced type 2 cytokine production and eosinophil function. In addition, IL-17F deficiency resulted in reduced colitis caused by dextran sulfate sodium, whereas IL-17 knockout mice developed more severe disease. Our results thus demonstrate that IL-17F is an important regulator of inflammatory responses that seems to function differently than IL-17 in immune responses and diseases.

Essential autocrine regulation by IL-21 in the generation of inflammatory T cells.

After activation, CD4+ helper T (T(H)) cells differentiate into distinct effector subsets that are characterized by their unique cytokine expression and immunoregulatory function. During this differentiation, T(H)1 and T(H)2 cells produce interferon-gamma and interleukin (IL)-4, respectively, as autocrine factors necessary for selective lineage commitment. A distinct T(H) subset, termed T(HIL-17), T(H)17 or inflammatory T(H) (T(H)i), has been recently identified as a distinct T(H) lineage mediating tissue inflammation. T(H)17 differentiation is initiated by transforming growth factor-beta and IL-6 (refs 5-7) and reinforced by IL-23 (ref. 8), in which signal transduction and activators of transcription (STAT)3 and retinoic acid receptor-related orphan receptor (ROR)-gamma mediate the lineage specification. T(H)17 cells produce IL-17, IL-17F and IL-22, all of which regulate inflammatory responses by tissue cells but have no importance in T(H)17 differentiation. Here we show that IL-21 is another cytokine highly expressed by mouse T(H)17 cells. IL-21 is induced by IL-6 in activated T cells, a process that is dependent on STAT3 but not ROR-gamma. IL-21 potently induces T(H)17 differentiation and suppresses Foxp3 expression, which requires STAT3 and ROR-gamma, which is encoded by Rorc. IL-21 deficiency impairs the generation of T(H)17 cells and results in protection against experimental autoimmune encephalomyelitis. IL-21 is therefore an autocrine cytokine that is sufficient and necessary for T(H)17 differentiation, and serves as a target for treating inflammatory diseases.

STAT3 regulates cytokine-mediated generation of inflammatory helper T cells.

Interleukin-17 (IL-17)-producing helper T (TH) cells, named as TH(IL-17), TH17, or inflammatory TH (THi), have been recently identified as a novel effector lineage. However, how cytokine signals mediate THi differentiation is unclear. We found that IL-6 functioned to up-regulate IL-23R and that IL-23 synergized with IL-6 in promoting THi generation. STAT3, activated by both IL-6 and IL-23, plays a critical role in THi development. A hyperactive form of STAT3 promoted THi development, whereas this differentiation process was greatly impaired in STAT3-deficient T cells. Moreover, STAT3 regulated the expression of retinoic acid receptor-related orphan receptor gamma-T (RORgamma t), a THi-specific transcriptional regulator; STAT3 deficiency impaired RORgamma t expression and led to elevated expression of T-box expressed in T cells (T-bet) and Forkhead box P3 (Foxp3). Our data thus demonstrate a pathway whereby cytokines regulate THi differentiation through a selective STAT transcription factor that functions to regulate lineage-specific gene expression.

Chromatin remodeling of interleukin-17 (IL-17)-IL-17F cytokine gene locus during inflammatory helper T cell differentiation.

During differentiation of naive CD4+ helper T (TH) cells into effector cells, specific cytokine gene loci undergo extensive changes in chromatin modification. A novel lineage of TH cells that is regulated by transforming growth factor-beta (TGFbeta) and interleukin-6 (IL-6) has been identified recently as promoting tissue inflammation. These inflammatory TH (THi) cells, also called TH17 or TH(IL-17), produce IL-17 and IL-17F, two highly homologous cytokines that have genes located in the same chromosomal region. Here, using chromatin immunoprecipitation techniques, we have demonstrated that similar to the regulation in TH1 and TH2 cell lineages, polarization of THi cells was accompanied by selective chromatin remodeling events. Histone H3 acetylation and Lys-4 tri-methylation were specifically associated with IL-17 and IL-17F gene promoters in THi lineage. At an early stage of T cell activation, histone acetylation on these promoters was greatly promoted by a combination of TGFbeta and IL-6, suggesting their synergistic role in initiating chromatin accessibility for transcription factors. Furthermore, we identified multiple noncoding sequences within the IL-17-IL-17F locus conserved across species. These elements were also associated with hyperacetylated histone 3 in a lineage-specific manner and may thus serve as potential regulatory regions. In summary, our results demonstrate for the first time that THi cell differentiation is associated with epigenetic changes in the IL-17-IL-17F locus, which suggests novel mechanisms in T cell functional regulation.

Regulation of T-cell receptor D beta 1 promoter by KLF5 through reiterated GC-rich motifs.

Rearrangement of T-cell receptor (TCR) and immunoglobulin genes by a common V(D)J recombination machinery is regulated by developmentally specific chromatin changes at the target locus, a process associated with transcription. At the TCRbeta locus, the Ebeta enhancer and the Dbeta1 promoter regulate germline transcription originating near the TCR Dbeta1 gene segment. The Dbeta1 promoter contains 3 GC-rich motifs that bind a common set of nuclear proteins from pro-T-cell lines. Mutations that diminish the binding of nuclear proteins also diminish the activity of the Dbeta1 promoter in transcriptional reporter assays. Using a yeast one-hybrid approach, 3 Krüppel-like factors-KLF3, KLF5, and KLF6-and a novel zinc finger protein were identified in a thymus library, all of which bound the GC-rich motif in a sequence-specific manner. Of these genes, KLF5 mRNA was expressed in a restricted manner in lymphoid cells and tissues, with highest expression in pro-T-cell lines and Rag-deficient thymocytes. Antibody supershift studies and chromatin immunoprecipitation assay confirmed that KLF5 bound the Dbeta1 promoter. In reporter gene assays, KLF5 but not KLF6 efficiently transactivated the Dbeta1 promoter, whereas a dominant-negative KLF5 construct inhibited reporter expression. These data suggest that reiterated GC motifs contribute to germline TCRbeta transcription through binding of KLF5 and other Krüppel family members and that restricted expression of KLF5 may contribute to lineage-specific regulation of germline TCRbeta transcription.

JAK2, complemented by a second signal from c-kit or flt-3, triggers extensive self-renewal of primary multipotential hemopoietic cells.

Defining signals that can support the self-renewal of multipotential hemopoietic progenitor cells (MHPCs) is pertinent to understanding leukemogenesis and may be relevant to developing stem cell-based therapies. Here we define a set of signals, JAK2 plus either c-kit or flt-3, which together can support extensive MHPC self-renewal. Phenotypically and functionally distinct populations of MHPCs were obtained, depending on which receptor tyrosine kinase, c-kit or flt-3, was activated. Self-renewal was abrogated in the absence of STAT5a/b, and in the presence of inhibitors targeting either the mitogen-activated protein kinase or phosphatidylinositol 3' kinase pathways. These findings suggest that a simple two-component signal can drive MHPC self-renewal.