T cell receptor-dependent activation of mTOR signaling in T cells is mediated by Carma1 and MALT1, but not Bcl10

PRRSV utilizes MALT1-regulated autophagy flux to switch virus spread and reserve

Porcine reproductive and respiratory syndrome virus (PRRSV) is a major swine pathogen, which can survive host antiviral immunity with various mechanisms. PRRSV infection induces macroautophagy/autophagy, facilitating virus replication. MALT1, a central immune regulator, was manipulated by PRRSV to optimize viral infection at different stages of the virus cycle. In this study, the key role of MALT1 in autophagy regulation during PRRSV infection was characterized, enlightening the role of autophagy flux in favor of virus spread and persistent infection. PRRSV-induced autophagy was confirmed to facilitate virus proliferation. Furthermore, autophagic fusion was dynamically regulated during PRRSV infection. Importantly, PRRSV-induced MALT1 facilitated autophagosome-lysosome fusion and autolysosome formation, thus contributing to autophagy flux and virus proliferation. Mechanically, MALT1 regulated autophagy via mediating MTOR-ULK1 and -TFEB signaling and affecting lysosomal homeostasis. MALT1 inhibition by inhibitor Mi-2 or RNAi induced lysosomal membrane permeabilization (LMP), leading to the block of autophagic fusion. Further, MALT1 overexpression alleviated PRRSV-induced LMP via inhibiting ROS generation. In addition, blocking autophagy flux suppressed virus release significantly, indicating that MALT1-maintained complete autophagy flux during PRRSV infection favors successful virus spread and its proliferation. In contrast, autophagosome accumulation upon MALT1 inhibition promoted PRRSV reserve for future virus proliferation once the autophagy flux recovers. Taken together, for the first time, these findings elucidate that MALT1 was utilized by PRRSV to regulate host autophagy flux, to determine the fate of virus for either proliferation or reserve.Abbreviations: 3-MA: 3-methyladenine; BafA1: bafilomycin A1; BFP/mBFP: monomeric blue fluorescent protein; CQ: chloroquine; DMSO: dimethyl sulfoxide; dsRNA: double-stranded RNA; GFP: green fluorescent protein; hpi: hours post infection; IFA: indirect immunofluorescence assay; LAMP1: lysosomal associated membrane protein 1; LGALS3: galectin 3; LLOMe: L-leucyl-L-leucine-methyl ester; LMP: lysosomal membrane permeabilization; mAb: monoclonal antibody; MALT1: MALT1 paracaspase; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MOI: multiplicity of infection; MTOR: mechanistic target of rapamycin kinase; NFKB/NF-κB: nuclear factor kappa B; nsp: nonstructural protein; ORF: open reading frame; pAb: polyclonal antibody; PRRSV: porcine reproductive and respiratory syndrome virus; PRRSV-N: PRRSV nucleocapsid protein; Rapa: rapamycin; RFP: red fluorescent protein; ROS: reactive oxygen species; SBI: SBI-0206965; siRNA: small interfering RNA; SQSTM1/p62: sequestosome 1; TCID50: 50% tissue culture infective dose; TFEB: transcription factor EB; ULK1: unc-51 like autophagy activating kinase 1.

MALT1 Protease Regulates T-Cell Immunity via the mTOR Pathway in Oral Lichen Planus

Oral lichen planus (OLP) is a T cell-mediated immune mucosal disease of unknown pathogenesis. Whether mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1), an intracellular signaling protein, is involved in the T-cell immune dysfunction of OLP remains elusive. MALT1 expression in local and peripheral T cells of OLP and controls was analyzed using immunohistochemistry, multiplex immunohistochemistry, and flow cytometry. The expression of MALT1 in activated Jurkat T cells incubated with either OLP plasma or interleukin (IL)-7/IL-15 was determined by flow cytometry. The effects of MALT1 and mechanistic target of rapamycin (mTOR) on T-cell immunity were investigated through western blot, CCK8 assay, and flow cytometry. The expression of MALT1 protein was elevated in local OLP T cells and mucosal-associated invariant T (MAIT) cells, while reduced in peripheral OLP T cells, MAIT cells, and follicular helper-like MAIT (MAITfh) cells. Stimulation with OLP plasma and IL-7/ IL-15 had no effect on MALT1 expression in activated Jurkat T cells. MALT1 protease-specific inhibitor (MI-2) induced mTOR phosphorylation, increased B-cell lymphoma 10 (BCL10) expression, inhibited T-cell proliferation, and promoted T-cell apoptosis. The combination of MI-2 and rapamycin increased MALT1 expression, further suppressed T-cell proliferation, and facilitated T-cell apoptosis. MALT1 expression is aberrant in both local lesions and peripheral blood of OLP. Inhibition of the mTOR pathway further enhances the suppression of T-cell proliferation and the promotion of apoptosis induced by the MALT1 inhibitor MI-2.

Pharmacological inhibition of MALT1 (mucosa-associated lymphoid tissue lymphoma translocation protein 1) induces ferroptosis in vascular smooth muscle cells

MALT1 (mucosa-associated lymphoid tissue lymphoma translocation protein 1) is a human paracaspase protein with proteolytic activity via its caspase-like domain. The pharmacological inhibition of MALT1 by MI-2, a specific chemical inhibitor, diminishes the response of endothelial cells to inflammatory stimuli. However, it is largely unknown how MALT1 regulates the functions of vascular smooth muscle cells (SMCs). This study aims to investigate the impact of MALT1 inhibition by MI-2 on the functions of vascular SMCs, both in vitro and in vivo. MI-2 treatment led to concentration- and time-dependent cell death of cultured aortic SMCs, which was rescued by the iron chelator deferoxamine (DFO) or ferrostatin-1 (Fer-1), a specific inhibitor of ferroptosis, but not by inhibitors of apoptosis (Z-VAD-fmk), pyroptosis (Z-YVAD-fmk), or necrosis (Necrostatin-1, Nec-1). MI-2 treatment downregulated the expression of glutathione peroxidase 4 (GPX4) and ferritin heavy polypeptide 1 (FTH1), which was prevented by pre-treatment with DFO or Fer-1. MI-2 treatment also activated autophagy, which was inhibited by Atg7 deficiency or bafilomycin A1 preventing MI-2-induced ferroptosis. MI-2 treatment reduced the cleavage of cylindromatosis (CYLD), a specific substrate of MALT1. Notably, MI-2 treatment led to a rapid loss of contractility in mouse aortas, which was prevented by co-incubation with Fer-1. Moreover, local application of MI-2 significantly reduced carotid neointima lesions and atherosclerosis in C57BL/6J mice and apolipoprotein-E knockout (ApoE-/-) mice, respectively, which were both ameliorated by co-treatment with Fer-1. In conclusion, the present study demonstrated that MALT1 inhibition induces ferroptosis of vascular SMCs, likely contributing to its amelioration of proliferative vascular diseases.

TCR ligand potency differentially impacts PD-1 inhibitory effects on diverse signaling pathways

Checkpoint blockade revolutionized cancer therapy, but we still lack a quantitative, mechanistic understanding of how inhibitory receptors affect diverse signaling pathways. To address this issue, we developed and applied a fluorescent intracellular live multiplex signal transduction activity reporter (FILMSTAR) system to analyze PD-1-induced suppressive effects. These studies identified pathways triggered solely by TCR or requiring both TCR and CD28 inputs. Using presenting cells differing in PD-L1 and CD80 expression while displaying TCR ligands of distinct potency, we found that PD-1-mediated inhibition primarily targets TCR-linked signals in a manner highly sensitive to peptide ligand quality. These findings help resolve discrepancies in existing data about the site(s) of PD-1 inhibition in T cells while emphasizing the importance of neoantigen potency in controlling the effects of checkpoint therapy.

Identification of an Ortholog of MALT1 from Shrimp That Induces NF-κB-Mediated Antiviral Immunity

MALT1 (mucosa-associated lymphoid tissue lymphoma translocation protein 1) serves as a pivotal mediator for NF-κB activation in response to a wide spectrum of transmembrane receptor stimuli. In the present study, a homolog of MALT1, named LvMALT1, is cloned from the Pacific white shrimp (Litopenaeus vannamei) and its potential function in shrimp innate immunity is explored. The open reading frame of LvMALT1 is 2364 bp that encodes 787 amino acids. The predicted LvMALT1 protein structure comprises a death domain, three immunoglobulin domains, and a caspase-like domain, exhibiting remarkable similarity to other homologs. LvMALT1 is a cytoplasmic-localized protein and could interact with LvTRAF6. Overexpression of LvMALT1 induces the activation of promoter elements governing the expression of several key antimicrobial peptides (AMPs), including penaeidins (PENs) and crustins (CRUs). Conversely, silencing of LvMALT1 leads to a reduction in the phosphorylation levels of Dorsal and Relish, along with a concomitant decline in the in vivo expression levels of multiple AMPs. Furthermore, LvMALT1 is prominently upregulated in response to a challenge by the white spot syndrome virus (WSSV), facilitating the NF-κB-mediated expression of AMPs as a defense against viral infection. Taken together, we identified a MALT1 homolog from the shrimp L. vannamei, which plays a positive role in the TRAF6/NF-κB/AMPs axis-mediated innate immunity.

Classic costimulatory interactions in MAIT cell responses: from gene expression to immune regulation

Mucosa-associated invariant T (MAIT) cells are evolutionarily conserved, innate-like T lymphocytes with enormous immunomodulatory potentials. Due to their strategic localization, their invariant T cell receptor (iTCR) specificity for major histocompatibility complex-related protein 1 (MR1) ligands of commensal and pathogenic bacterial origin, and their sensitivity to infection-elicited cytokines, MAIT cells are best known for their antimicrobial characteristics. However, they are thought to also play important parts in the contexts of cancer, autoimmunity, vaccine-induced immunity, and tissue repair. While cognate MR1 ligands and cytokine cues govern MAIT cell maturation, polarization, and peripheral activation, other signal transduction pathways, including those mediated by costimulatory interactions, regulate MAIT cell responses. Activated MAIT cells exhibit cytolytic activities and secrete potent inflammatory cytokines of their own, thus transregulating the biological behaviors of several other cell types, including dendritic cells, macrophages, natural killer cells, conventional T cells, and B cells, with significant implications in health and disease. Therefore, an in-depth understanding of how costimulatory pathways control MAIT cell responses may introduce new targets for optimized MR1/MAIT cell-based interventions. Herein, we compare and contrast MAIT cells and mainstream T cells for their expression of classic costimulatory molecules belonging to the immunoglobulin superfamily and the tumor necrosis factor (TNF)/TNF receptor superfamily, based not only on the available literature but also on our transcriptomic analyses. We discuss how these molecules participate in MAIT cells' development and activities. Finally, we introduce several pressing questions vis-à-vis MAIT cell costimulation and offer new directions for future research in this area.

CARD11 dominant negative mutation leads to altered human Natural Killer cell homeostasis

Dominant negative mutations in CARD11 have been reported in patients with immune dysregulation, severe atopic features, and variable T cell alterations. Data on Natural killer (NK) cells from affected patients are lacking. We report on a 12-year-old boy with severe atopic dermatitis, food induced anaphylaxis and hypogammaglobulinemia harbouring a novel de novo heterozygous variant c.169G > A; p.Glu57Lys in CARD11. The dominant negative effect of this mutation was confirmed on both CD4+ and CD8+. CTLA4+Foxp3+CD4+ Tregs were severely reduced. Patient's NK cells showed reduced expression of NKp46, NKG2D and CD69. Patient's CD56bright NK cells showed in vitro impaired production of IFN-γ. Steady state pS6 levels on patient's NK cells were increased and remained elevated upon IL2 + IL12 + IL18 overnight stimulation. Overall, the effect of CARD11 mutation on mTORC1 differs between T and NK cells. These findings may explain the increased susceptibility to viral infections and the reduced immune surveillance in affected patients.

NFκB signaling in T cell memory

Memory T cells play an essential role in protecting against infectious diseases and cancer and contribute to autoimmunity and transplant rejection. Understanding how they are generated and maintained in the context of infection or vaccination holds promise to improve current immune-based therapies. At the beginning of any immune response, naïve T cells are activated and differentiate into cells with effector function capabilities. In the context of infection, most of these cells die once the pathogenic antigen has been cleared. Only a few of them persist and differentiate into memory T cells. These memory T cells are essential to host immunity because they are long-lived and can perform effector functions immediately upon re-infection. How a cell becomes a memory T cell and continues being one for months and even years past the initial infection is still not fully understood. Recent reviews have thoroughly discussed the transcriptional, epigenomic, and metabolic mechanisms that govern T cell memory differentiation. Yet much less is known of how signaling pathways that are common circuitries of multiple environmental signals regulate T cell outcome and, precisely, T cell memory. The function of the NFκB signaling system is perhaps best understood in innate cells. Recent findings suggest that NFκB signaling plays an essential and unique role in generating and maintaining CD8 T cell memory. This review aims to summarize these findings and discuss the remaining questions in the field.

Cotargeting of BTK and MALT1 overcomes resistance to BTK inhibitors in mantle cell lymphoma

Bruton's tyrosine kinase (BTK) is a proven target in mantle cell lymphoma (MCL), an aggressive subtype of non-Hodgkin lymphoma. However, resistance to BTK inhibitors is a major clinical challenge. We here report that MALT1 is one of the top overexpressed genes in ibrutinib-resistant MCL cells, while expression of CARD11, which is upstream of MALT1, is decreased. MALT1 genetic knockout or inhibition produced dramatic defects in MCL cell growth regardless of ibrutinib sensitivity. Conversely, CARD11-knockout cells showed antitumor effects only in ibrutinib-sensitive cells, suggesting that MALT1 overexpression could drive ibrutinib resistance via bypassing BTK/CARD11 signaling. Additionally, BTK knockdown and MALT1 knockout markedly impaired MCL tumor migration and dissemination, and MALT1 pharmacological inhibition decreased MCL cell viability, adhesion, and migration by suppressing NF-κB, PI3K/AKT/mTOR, and integrin signaling. Importantly, cotargeting MALT1 with safimaltib and BTK with pirtobrutinib induced potent anti-MCL activity in ibrutinib-resistant MCL cell lines and patient-derived xenografts. Therefore, we conclude that MALT1 overexpression associates with resistance to BTK inhibitors in MCL, targeting abnormal MALT1 activity could be a promising therapeutic strategy to overcome BTK inhibitor resistance, and cotargeting of MALT1 and BTK should improve MCL treatment efficacy and durability as well as patient outcomes.

Elevated IgE from attenuated CARD11 signaling: lessons from atopic mice and humans

CARD11 encodes a large scaffold protein responsible for integrating antigen-receptor engagement with downstream signaling to NF-kB and other outputs in lymphocytes. Over the past 10 years, several human-inborn errors of immunity have been linked to pathogenic CARD11 mutations. Most recently, severe atopic patients were discovered that carried heterozygous dominant-negative CARD11 mutations. Here, we review the mechanistic connections between attenuated CARD11 signaling, elevated IgE, and atopy, comparing and contrasting key insights from both human patients and murine models. Continued investigation of abnormal CARD11 signaling in both contexts should inform novel therapeutic strategies to combat allergic pathogenesis.

Expanding spectrum, intrafamilial diversity, and therapeutic challenges from 15 patients with heterozygous CARD11-associated diseases: A single center experience

CARD11-associated diseases are monogenic inborn errors of immunity involving immunodeficiency, predisposition to malignancy and immune dysregulation such as lymphoproliferation, inflammation, atopic and autoimmune manifestations. Defects in CARD11 can present as mutations that confer a complete or a partial loss of function (LOF) or contrarily, a gain of function (GOF) of the affected gene product. We report clinical characteristics, immunophenotypes and genotypes of 15 patients from our center presenting with CARD11-associated diseases. Index cases are pediatric patients followed in our immunology division who had access to next generation sequencing studies. Variant significance was defined by functional analysis in cultured cells transfected with a wild type and/or with mutated hCARD11 constructs. Cytoplasmic aggregation of CARD11 products was evaluated by immunofluorescence. Nine index patients with 9 unique heterozygous CARD11 variants were identified. At the time of the identification, 7 variants previously unreported required functional validation. Altogether, four variants showed a GOF effect as well a spontaneous aggregation in the cytoplasm, leading to B cell expansion with NF-κB and T cell anergy (BENTA) diagnosis. Additional four variants showing a LOF activity were considered as causative of CARD11-associated atopy with dominant interference of NF-kB signaling (CADINS). The remaining variant exhibited a neutral functional assay excluding its carrier from further analysis. Family segregation studies expanded to 15 individuals the number of patients presenting CARD11-associated disease. A thorough clinical, immunophenotypical, and therapeutic management evaluation was performed on these patients (5 BENTA and 10 CADINS). A remarkable variability of disease expression was clearly noted among BENTA as well as in CADINS patients, even within multiplex families. Identification of novel CARD11 variants required functional studies to validate their pathogenic activity. In our cohort BENTA phenotype exhibited a more severe and expanded clinical spectrum than previously reported, e.g., severe hematological and extra hematological autoimmunity and 3 fatal outcomes. The growing number of patients with dysmorphic facial features strengthen the inclusion of extra-immune characteristics as part of the CADINS spectrum. CARD11-associated diseases represent a challenging group of disorders from the diagnostic and therapeutic standpoint, especially BENTA cases that can undergo a more severe progression than previously described.

The role of the CBM complex in allergic inflammation and disease

The caspase activation and recruitment domain-coiled-coil (CARD-CC) family of proteins-CARD9, CARD10, CARD11, and CARD14-is collectively expressed across nearly all tissues of the body and is a crucial mediator of immunologic signaling as part of the CARD-B-cell lymphoma/leukemia 10-mucosa-associated lymphoid tissue lymphoma translocation protein 1 (CBM) complex. Dysfunction or dysregulation of CBM proteins has been linked to numerous clinical manifestations known as "CBM-opathies." The CBM-opathy spectrum encompasses diseases ranging from mucocutaneous fungal infections and psoriasis to combined immunodeficiency and lymphoproliferative diseases; however, there is accumulating evidence that the CARD-CC family members also contribute to the pathogenesis and progression of allergic inflammation and allergic diseases. Here, we review the 4 CARD-CC paralogs, as well as B-cell lymphoma/leukemia 10 and mucosa-associated lymphoid tissue lymphoma translocation protein 1, and their individual and collective roles in the pathogenesis and progression of allergic inflammation and 4 major allergic diseases (allergic asthma, atopic dermatitis, food allergy, and allergic rhinitis).

Atopy as Immune Dysregulation: Offender Genes and Targets

Allergic diseases are a heterogeneous group of disorders resulting from exaggerated type 2 inflammation. Although typically viewed as polygenic multifactorial disorders caused by the interaction of several genes with the environment, we have come to appreciate that allergic diseases can also be caused by monogenic variants affecting the immune system and the skin epithelial barrier. Through a myriad of genetic association studies and high-throughput sequencing tools, many monogenic and polygenic culprits of allergic diseases have been described. Identifying the genetic causes of atopy has shaped our understanding of how these conditions occur and how they may be treated and even prevented. Precision diagnostic tools and therapies that address the specific molecular pathways implicated in allergic inflammation provide exciting opportunities to improve our care for patients across the field of allergy and immunology. Here, we highlight offender genes implicated in polygenic and monogenic allergic diseases and list targeted therapeutic approaches that address these disrupted pathways.

Porcine Reproductive and Respiratory Syndrome Virus Adapts Antiviral Innate Immunity via Manipulating MALT1

To fulfill virus replication and persistent infection in hosts, viruses have to find ways to compromise innate immunity, including timely impedance on antiviral RNases and inflammatory responses. Porcine reproductive and respiratory syndrome virus (PRRSV) is a major swine pathogen causing immune suppression. MALT1 is a central immune regulator in both innate and adaptive immunity. In this study, MALT1 was confirmed to be induced rapidly upon PRRSV infection and mediate the degradation of two anti-PRRSV RNases, MCPIP1 and N4BP1, relying on its proteolytic activity, consequently facilitating PRRSV replication. Multiple PRRSV nsps, including nsp11, nsp7β, and nsp4, contributed to MALT1 elicitation. Interestingly, the elevated expression of MALT1 began to decrease once intracellular viral expression reached a high enough level. Higher infection dose brought earlier MALT1 inflection. Further, PRRSV nsp6 mediated significant MALT1 degradation via ubiquitination-proteasome pathway. Downregulation of MALT1 suppressed NF-κB signals, leading to the decrease in proinflammatory cytokine expression. In conclusion, MALT1 expression was manipulated by PRRSV in an elaborate manner to antagonize precisely the antiviral effects of host RNases without excessive and continuous activation of inflammatory responses. These findings throw light on the machinery of PRRSV to build homeostasis in infected immune system for viral settlement.

Post-translational modification of MALT1 and its role in B cell- and T cell-related diseases

Mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) is a multifunctional protein. MALT1 functions as an adaptor protein to assemble and recruit proteins such as B-cell lymphoma 10 (BCL10) and caspase-recruitment domain (CARD)-containing coiled-coil protein 11 (CARD11). Conversely it also acts as a paracaspase to cleave specified substrates. Because of its involvement in immunity, inflammation and cancer through its dual functions of scaffolding and catalytic activity, MALT1 is becoming a promising therapeutic target in B cell- and T cell-related diseases. There is growing evidence that the function of MALT1 is subtly modulated via post-translational modifications. This review summarized recent progress in relevant studies regarding the physiological and pathophysiological functions of MALT1, post-translational modifications of MALT1 and its role in B cell- and T cell- related diseases. In addition, the current available MALT1 inhibitors were also discussed.

Mechanistic impact of oligomer poisoning by dominant-negative CARD11 variants

The CARD11 scaffold controls antigen receptor signaling to NF-κB, JNK, and mTOR. Three classes of germline mutations in CARD11 cause Primary Immunodeficiency, including homozygous loss-of-function (LOF) mutations in CARD11 deficiency, heterozygous gain-of-function (GOF) mutations in BENTA disease, and heterozygous dominant-negative LOF mutations in CADINS. Here, we characterize LOF CARD11 mutants with a range of dominant-negative activities to identify the mechanistic properties that cause these variants to exert dominant effects when heterozygous. We find that strong dominant negatives can poison signaling from mixed wild-type:mutant oligomers at two steps in the CARD11 signaling cycle, at the Opening Step and at the Cofactor Association Step. Our findings provide evidence that CARD11 oligomer subunits cooperate in at least two steps during antigen receptor signaling and reveal how different LOF mutations in the same oligomeric signaling hub may cause disease with different inheritance patterns.

T cell receptor (TCR) signaling in health and disease

Interaction of the T cell receptor (TCR) with an MHC-antigenic peptide complex results in changes at the molecular and cellular levels in T cells. The outside environmental cues are translated into various signal transduction pathways within the cell, which mediate the activation of various genes with the help of specific transcription factors. These signaling networks propagate with the help of various effector enzymes, such as kinases, phosphatases, and phospholipases. Integration of these disparate signal transduction pathways is done with the help of adaptor proteins that are non-enzymatic in function and that serve as a scaffold for various protein-protein interactions. This process aids in connecting the proximal to distal signaling pathways, thereby contributing to the full activation of T cells. This review provides a comprehensive snapshot of the various molecules involved in regulating T cell receptor signaling, covering both enzymes and adaptors, and will discuss their role in human disease.

Exposure to Stearate Activates the IRE1α/XBP-1 Pathway in 3T3-L1 Adipocytes

In the endoplasmic reticulum (ER), accumulation of abnormal proteins with malformed higher-order structures activates signaling pathways (inositol-requiring enzyme 1α (IRE1α)/X-box binding protein 1 (XBP-1) pathway, protein kinase RNA-activated-like endoplasmic reticulum kinase (PERK)/CCAAT/enhancer binding protein-homologous protein (CHOP) pathway and activating transcription factor 6α (ATF6α) pathway) that result in a cellular response suppressing the production of abnormal proteins or inducing apoptosis. These responses are collectively known as the unfolded protein response (UPR). Recently, it has been suggested that the UPR induced by saturated fatty acids in hepatocytes and pancreatic β cells is involved in the development of metabolic diseases such as diabetes. The effect of palmitate, a saturated fatty acid, on the UPR has also been investigated in adipocytes, which are associated with the development of metabolic disorders, but the results were inconclusive. Therefore, as the major saturated fatty acids present in the daily diet are palmitate and stearate, we examined the effects of these saturated fatty acids on UPR in adipocytes. Here, we show that saturated fatty acids caused limited activation of the UPR in adipocytes. Exposure to stearate for several hours elevated the ratio of spliced XBP-1 mRNA, and this effect was stronger than that of palmitate. Moreover, the phosphorylation level of IRE1α, upstream of XBP-1 and expression levels of its downstream targets such as DNAJB9 and Pdia6 were elevated in 3T3-L1 adipocytes exposed to stearate. On the other hand, stearate did not affect the phosphorylation of PERK, its activation of CHOP, or the cleavage of ATF6α. Thus, in adipocytes, exposure to stearate activates the UPR via the IRE1α/XBP-1 pathway, but not the PERK/CHOP and ATF6α pathway.

Gene Body Methylation of the Lymphocyte-Specific Gene CARD11 Results in Its Overexpression and Regulates Cancer mTOR Signaling

Investigations into the function of nonpromoter DNA methylation have yielded new insights into epigenetic regulation of gene expression. Previous studies have highlighted the importance of distinguishing between DNA methylation in discrete functional regions; however, integrated nonpromoter DNA methylation and gene expression analyses across a wide number of tumor types and corresponding normal tissues have not been performed. Through integrated analysis of gene expression and DNA methylation profiles, we examined 32 tumor types and identified 57 tumor suppressors and oncogenes out of 260 genes exhibiting a correlation of > 0.5 between gene body methylation and gene expression in at least one tumor type. The lymphocyte-specific gene CARD11 exhibits robust association between gene body methylation and expression across 19 of 32 tumor types examined. It is significantly overexpressed in kidney renal cell carcinoma (KIRC) and lung adenocarcinoma (LUAD) tumor tissues in comparison with respective control samples; and is significantly associated with lower overall survival in KIRC. Contrary to its canonical function in lymphocyte NFκB activation, CARD11 activates the mTOR pathway in KIRC and LUAD, resulting in suppressed autophagy. Furthermore, demethylation of a CpG island within the gene body of CARD11 decreases gene expression. Collectively, our study highlights how DNA methylation outside the promoter region can impact tumor progression. IMPLICATIONS: Our study describes a novel regulatory role of gene body DNA methylation-dependent CARD11 expression on mTOR signaling and its impact on tumor progression.

Non-Stimulatory pMHC Enhance CD8 T Cell Effector Functions by Recruiting Coreceptor-Bound Lck

Under physiological conditions, CD8⁺ T cells need to recognize low numbers of antigenic pMHC class I complexes in the presence of a surplus of non-stimulatory, self pMHC class I on the surface of the APC. Non-stimulatory pMHC have been shown to enhance CD8⁺ T cell responses to low amounts of antigenic pMHC, in a phenomenon called co-agonism, but the physiological significance and molecular mechanism of this phenomenon are still poorly understood. Our data show that co-agonist pMHC class I complexes recruit CD8-bound Lck to the immune synapse to modulate CD8⁺ T cell signaling pathways, resulting in enhanced CD8⁺ T cell effector functions and proliferation, both in vitro and in vivo. Moreover, co-agonism can boost T cell proliferation through an extrinsic mechanism, with co-agonism primed CD8⁺ T cells enhancing Akt pathway activation and proliferation in neighboring CD8⁺ T cells primed with low amounts of antigen.

Mechanistic understanding of the combined immunodeficiency in complete human CARD11 deficiency

BACKGROUND

Germline pathogenic variants impairing the caspase recruitment domain family member 11 (CARD11)-B cell chronic lymphocytic leukemia/lymphoma 10 (BCL10)-MALT1 paracaspase (MALT1) (CBM) complex are associated with diverse human diseases including combined immunodeficiency (CID), atopy, and lymphoproliferation. However, the impact of CARD11 deficiency on human B-cell development, signaling, and function is incompletely understood.

OBJECTIVES

This study sought to determine the cellular, immunological, and biochemical basis of disease for 2 unrelated patients who presented with profound CID associated with viral and fungal respiratory infections, interstitial lung disease, and severe colitis.

METHODS

Patients underwent next-generation sequencing, immunophenotyping by flow cytometry, signaling assays by immunoblot, and transcriptome profiling by RNA-sequencing.

RESULTS

Both patients carried identical novel pathogenic biallelic loss-of-function variants in CARD11 (c.2509C>T; p.Arg837∗) leading to undetectable protein expression. This variant prevented CBM complex formation, severely impairing the activation of nuclear factor-κB, c-Jun N-terminal kinase, and MALT1 paracaspase activity in B and T cells. This functional defect resulted in a developmental block in B cells at the naive and type 1 transitional B-cell stage and impaired circulating T follicular helper cell (cT_FH) development, which was associated with impaired antibody responses and absent germinal center structures on lymph node histology. Transcriptomics indicated that CARD11-dependent signaling is essential for immune signaling pathways involved in the development of these cells. Both patients underwent hematopoietic stem cell transplantations, which led to functional normalization.

CONCLUSIONS

Complete human CARD11 deficiency causes profound CID by impairing naive/type 1 B-cell and cT_FH cell development and abolishing activation of MALT1 paracaspase, NF-κB, and JNK activity. Hematopoietic stem cell transplantation functionally restores impaired signaling pathways.

Regulation of Intrinsic and Bystander T Follicular Helper Cell Differentiation and Autoimmunity by Tsc1

T Follicular helper (Tfh) cells promote germinal center (GC) B cell responses to develop effective humoral immunity against pathogens. However, dysregulated Tfh cells can also trigger autoantibody production and the development of autoimmune diseases. We report here that Tsc1, a regulator for mTOR signaling, plays differential roles in Tfh cell/GC B cell responses in the steady state and in immune responses to antigen immunization. In the steady state, Tsc1 in T cells intrinsically suppresses spontaneous GC-Tfh cell differentiation and subsequent GC-B cell formation and autoantibody production. In immune responses to antigen immunization, Tsc1 in T cells is required for efficient GC-Tfh cell expansion, GC-B cell induction, and antigen-specific antibody responses, at least in part via promoting GC-Tfh cell mitochondrial integrity and survival. Interestingly, in mixed bone marrow chimeric mice reconstituted with both wild-type and T cell-specific Tsc1-deficient bone marrow cells, Tsc1 deficiency leads to enhanced GC-Tfh cell differentiation of wild-type CD4 T cells and increased accumulation of wild-type T regulatory cells and T follicular regulatory cells. Such bystander GC-Tfh cell differentiation suggests a potential mechanism that could trigger self-reactive GC-Tfh cell/GC responses and autoimmunity via neighboring GC-Tfh cells.

Differential controls of MAIT cell effector polarization by mTORC1/mTORC2 via integrating cytokine and costimulatory signals

Mucosal-associated invariant T (MAIT) cells have important functions in immune responses against pathogens and in diseases, but mechanisms controlling MAIT cell development and effector lineage differentiation remain unclear. Here, we report that IL-2/IL-15 receptor β chain and inducible costimulatory (ICOS) not only serve as lineage-specific markers for IFN-γ-producing MAIT1 and IL-17A-producing MAIT17 cells, but are also important for their differentiation, respectively. Both IL-2 and IL-15 induce mTOR activation, T-bet upregulation, and subsequent MAIT cell, especially MAIT1 cell, expansion. By contrast, IL-1β induces more MAIT17 than MAIT1 cells, while IL-23 alone promotes MAIT17 cell proliferation and survival, but synergizes with IL-1β to induce strong MAIT17 cell expansion in an mTOR-dependent manner. Moreover, mTOR is dispensable for early MAIT cell development, yet pivotal for MAIT cell effector differentiation. Our results thus show that mTORC2 integrates signals from ICOS and IL-1βR/IL-23R to exert a crucial role for MAIT17 differentiation, while the IL-2/IL-15R-mTORC1-T-bet axis ensures MAIT1 differentiation.

Human MALT1 deficiency and predisposition to infections

Human germline MALT1 deficiency is an inborn error of immunity characterized by recurrent bacterial, viral, and fungal infections, periodontal disease, enteropathy, dermatitis, and failure to thrive. The number of identified MALT1-deficient patients have greatly increased in the past two years, which has significantly improved our understanding of the clinical features of this disorder. Patients frequently experience infections affecting the respiratory, skin, gastrointestinal, and blood systems. The most frequently detected pathogens are Staphylococcus aureus, Candida albicans, and cytomegalovirus. Enhanced susceptibility to S. aureus and C. albicans is likely due to impaired Th17 immunity, similar to STAT3 and IL-17 pathway deficiencies.

Cellular CARD11 Inhibits the Fusogenic Activity of Newcastle Disease Virus via CBM Signalosome-Mediated Furin Reduction in Chicken Fibroblasts

Newcastle disease virus (NDV) causes an infectious disease that poses a major threat to poultry health. Our previous study identified a chicken brain-specific caspase recruitment domain-containing protein 11 (CARD11) that was upregulated in chicken neurons and inhibited NDV replication. This raises the question of whether CARD11 plays a role in inhibiting viruses in non-neural cells. Here, chicken fibroblasts were used as a non-neural cell model to investigate the role. CARD11 expression was not significantly upregulated by either velogenic or lentogenic NDV infection in chicken fibroblasts. Viral replication was decreased in DF-1 cells stably overexpressing CARD11, while viral growth was significantly increased in the CARD11-knockdown DF-1 cell line. Moreover, CARD11 colocalized with the viral P protein and aggregated around the fibroblast nucleus, suggesting that an interaction existed between CARD11 and the viral P protein; this interaction was further examined by suppressing viral RNA polymerase activity by using a minigenome assay. Viral replication was inhibited by CARD11 in fibroblasts, and this result was consistent with our previous report in chicken neurons. Importantly, CARD11 was observed to reduce the syncytia induced by either velogenic virus infection or viral haemagglutinin-neuraminidase (HN) and F cotransfection in fibroblasts. We found that CARD11 inhibited the expression of the host protease furin, which is essential for cleavage of the viral F protein to trigger fusogenic activity. Furthermore, the CARD11-Bcl10-MALT1 (CBM) signalosome was found to suppress furin expression, which resulted in a reduction in the cleavage efficiency of the viral F protein to further inhibit viral syncytia. Taken together, our findings mainly demonstrated a novel CARD11 inhibitory mechanism for viral fusogenic activity in chicken fibroblasts, and this mechanism explains the antiviral roles of this molecule in NDV pathogenesis.

GLS1-mediated glutaminolysis unbridled by MALT1 protease promotes psoriasis pathogenesis

Psoriasis is a severe disease associated with the disturbance of metabolism and inflammation, but the molecular mechanisms underlying these aspects of psoriasis pathology are poorly understood. Here, we report that glutaminase 1-mediated (GLS1-mediated) glutaminolysis was aberrantly activated in patients with psoriasis and in psoriasis-like mouse models, which promoted Th17 and γδ T17 (IL-17A-producing γδ T) cell differentiation through enhancement of histone H3 acetylation of the Il17a promoter, thereby contributing to the immune imbalance and development of psoriasis. We further demonstrate that mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) protease was constitutively active in psoriatic CD4+ and γδ T cells, thereby supporting GLS1 expression by stabilizing c-Jun, which directly binds to the GLS1 promoter region. Blocking the activity of either GLS1 or MALT1 protease resolved Th17 and γδ T17 cell differentiation and epidermal hyperplasia in the psoriasis-like mouse models. Finally, IL-17A enhanced GLS1 expression via the MALT1/cJun pathway in keratinocytes, resulting in hyperproliferation of and chemokine production by keratinocytes. Our findings identify the role of the MALT1/cJun/GLS1/glutaminolysis/H3 acetylation/T17 axis in psoriasis pathogenesis and reveal potential therapeutic targets for this disease.

Immune dysregulation in patients with RAG deficiency and other forms of combined immune deficiency

Traditionally, primary immune deficiencies have been defined based on increased susceptibility to recurrent and/or severe infections. However, immune dysregulation, manifesting with autoimmunity or hyperinflammatory disease, has emerged as a common feature. This is especially true in patients affected by combined immune deficiency (CID), a group of disorders caused by genetic defects that impair, but do not completely abolish, T-cell function. Hypomorphic mutations in the recombination activating genes RAG1 and RAG2 represent the prototype of the broad spectrum of clinical and immunological phenotypes associated with CID. The study of patients with RAG deficiency and with other forms of CID has revealed distinct abnormalities in central and peripheral T- and B-cell tolerance as the key mechanisms involved in immune dysregulation. Understanding the pathophysiology of autoimmunity and hyperinflammation in these disorders may also permit more targeted therapeutic interventions.

Mutual regulation of metabolic processes and proinflammatory NF-κB signaling

The nuclear factor kappa B (NF-κB) signaling system, a key regulator of immunologic processes, also affects a plethora of metabolic changes associated with inflammation and the immune response. NF-κB-regulating signaling cascades, in concert with NF-κB-mediated transcriptional events, control the metabolism at several levels. NF-κB modulates apical components of metabolic processes including metabolic hormones such as insulin and glucagon, the cellular master switches 5' AMP-activated protein kinase and mTOR, and also numerous metabolic enzymes and their respective regulators. Vice versa, metabolic enzymes and their products also exert multilevel control of NF-κB activity, thereby creating a highly connected regulatory network. These insights have resulted in the identification of the noncanonical IκB kinase kinases IκB kinase ɛ and TBK1, which are upregulated by overnutrition, and may therefore be suitable potential therapeutic targets for metabolic syndromes. An inhibitor interfering with the activity of both kinases reduces obesity-related metabolic dysfunctions in mouse models and the encouraging results from a recent clinical trial indicate that targeting these NF-κB pathway components improves glucose homeostasis in a subset of patients with type 2 diabetes.

Negative control of diacylglycerol kinase ζ-mediated inhibition of T cell receptor signaling by nuclear sequestration in mice

Diacylglycerol kinases (DGKs) play important roles in restraining diacylglycerol (DAG)-mediated signaling. Within the DGK family, the ζ isoform appears to be the most important isoform in T cells for controlling their development and function. DGKζ has been demonstrated to regulate T cell maturation, activation, anergy, effector/memory differentiation, defense against microbial infection, and antitumor immunity. Given its critical functions, DGKζ function should be tightly regulated to ensure proper signal transduction; however, mechanisms that control DGKζ function are still poorly understood. We report here that DGKζ dynamically translocates from the cytosol into the nuclei in T cells after TCR stimulation. In mice, DGKζ mutant defective in nuclear localization displayed enhanced ability to inhibit TCR-induced DAG-mediated signaling in primary T cells, maturation of conventional αβT and iNKT cells, and activation of peripheral T cells compared with WT DGKζ. Our study reveals for the first time nuclear sequestration of DGKζ as a negative control mechanism to spatially restrain it from terminating DAG mediated signaling in T cells. Our data suggest that manipulation of DGKζ nucleus-cytosol shuttling as a novel strategy to modulate DGKζ activity and immune responses for treatment of autoimmune diseases and cancer.

Regulation and repurposing of nutrient sensing and autophagy in innate immunity

Nutrients not only act as building blocks but also as signaling molecules. Nutrient-availability promotes cell growth and proliferation and suppresses catabolic processes, such as macroautophagy/autophagy. These effects are mediated by checkpoint kinases such as MTOR (mechanistic target of rapamycin kinase), which is activated by amino acids and growth factors, and AMP-activated protein kinase (AMPK), which is activated by low levels of glucose or ATP. These kinases have wide-ranging activities that can be co-opted by immune cells upon exposure to danger signals, cytokines or pathogens. Here, we discuss recent insight into the regulation and repurposing of nutrient-sensing responses by the innate immune system during infection. Moreover, we examine how natural mutations and pathogen-mediated interventions can alter the balance between anabolic and autophagic pathways leading to a breakdown in tissue homeostasis and/or host defense.Abbreviations: AKT1/PKB: AKT serine/threonine kinase 1; ATG: autophagy related; BECN1: beclin 1; CGAS: cyclic GMP-AMP synthase; EIF2AK4/GCN2: eukaryotic translation initiation factor 2 alpha kinase 4; ER: endoplasmic reticulum; FFAR: free fatty acid receptor; GABARAP: GABA type A receptor-associated protein; IFN: interferon; IL: interleukin; LAP: LC3-associated phagocytosis; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MAP3K7/TAK1: mitogen-activated protein kinase kinase kinase 7; MAPK: mitogen-activated protein kinase; MTOR: mechanistic target of rapamycin kinase; NLR: NOD (nucleotide-binding oligomerization domain) and leucine-rich repeat containing proteins; PI3K, phosphoinositide 3-kinase; PRR: pattern-recognition receptor; PtdIns3K: phosphatidylinositol 3-kinase; RALB: RAS like proto-oncogene B; RHEB: Ras homolog, MTORC1 binding; RIPK1: receptor interacting serine/threonine kinase 1; RRAG: Ras related GTP binding; SQSTM1/p62: sequestosome 1; STING1/TMEM173: stimulator of interferon response cGAMP interactor 1; STK11/LKB1: serine/threonine kinase 11; TBK1: TANK binding kinase 1; TLR: toll like receptor; TNF: tumor necrosis factor; TRAF6: TNF receptor associated factor 6; TRIM: tripartite motif protein; ULK1: unc-51 like autophagy activating kinase 1; V-ATPase: vacuolar-type H⁺-proton-translocating ATPase.

Germline CBM-opathies: From immunodeficiency to atopy

Caspase recruitment domain (CARD) protein-B cell CLL/lymphoma 10 (BCL10)-MALT1 paracaspase (MALT1) [CBM] complexes are critical signaling adaptors that facilitate immune and inflammatory responses downstream of both cell surface and intracellular receptors. Germline mutations that alter the function of members of this complex (termed CBM-opathies) cause a broad array of clinical phenotypes, ranging from profound combined immunodeficiency to B-cell lymphocytosis. With an increasing number of patients being described in recent years, the clinical spectrum of diseases associated with CBM-opathies is rapidly expanding and becoming unexpectedly heterogeneous. Here we review major discoveries that have shaped our understanding of CBM complex biology, and we provide an overview of the clinical presentation, diagnostic approach, and treatment options for those carrying germline mutations affecting CARD9, CARD11, CARD14, BCL10, and MALT1.

mTOR signaling at the crossroads of environmental signals and T-cell fate decisions

The evolutionarily conserved serine/threonine kinase mTOR (mechanistic target of rapamycin) forms the distinct protein complexes mTORC1 and mTORC2 and integrates signals from the environment to coordinate downstream signaling events and various cellular processes. T cells rely on mTOR activity for their development and to establish their homeostasis and functional fitness. Here, we review recent progress in our understanding of the upstream signaling and downstream targets of mTOR. We also provide an updated overview of the roles of mTOR in T-cell development, homeostasis, activation, and effector-cell fate decisions, as well as its important impacts on the suppressive activity of regulatory T cells. Moreover, we summarize the emerging roles of mTOR in T-cell exhaustion and transdifferentiation. A better understanding of the contribution of mTOR to T-cell fate decisions will ultimately aid in the therapeutic targeting of mTOR in human disease.

Primary Atopic Disorders

Primary atopic disorders describes a series of monogenic diseases that have allergy- or atopic effector–related symptoms as a substantial feature. The underlying pathogenic genetic lesions help illustrate fundamental pathways in atopy, opening up diagnostic and therapeutic options for further study in those patients, but ultimately for common allergic diseases as well. Key pathways affected in these disorders include T cell receptor and B cell receptor signaling, cytokine signaling, skin barrier function, and mast cell function, as well as pathways that have not yet been elucidated. While comorbidities such as classically syndromic presentation or immune deficiency are often present, in some cases allergy alone is the presenting symptom, suggesting that commonly encountered allergic diseases exist on a spectrum of monogenic and complex genetic etiologies that are impacted by environmental risk factors.

DGK α and ζ Activities Control TH1 and TH17 Cell Differentiation

CD4⁺ T helper (T_H) cells are critical for protective adaptive immunity against pathogens, and they also contribute to the pathogenesis of autoimmune diseases. How T_H differentiation is regulated by the TCR's downstream signaling is still poorly understood. We describe here that diacylglycerol kinases (DGKs), which are enzymes that convert diacylglycerol (DAG) to phosphatidic acid, exert differential effects on T_H cell differentiation in a DGK dosage-dependent manner. A deficiency of either DGKα or ζ selectively impaired T_H1 differentiation without obviously affecting T_H2 and T_H17 differentiation. However, simultaneous ablation of both DGKα and ζ promoted T_H1 and T_H17 differentiation in vitro and in vivo, leading to exacerbated airway inflammation. Furthermore, we demonstrate that dysregulation of T_H17 differentiation of DGKα and ζ double-deficient CD4⁺ T cells was, at least in part, caused by increased mTOR complex 1/S6K1 signaling.

Paracaspase MALT1 regulates glioma cell survival by controlling endo-lysosome homeostasis

Glioblastoma is one of the most lethal forms of adult cancer with a median survival of around 15 months. A potential treatment strategy involves targeting glioblastoma stem-like cells (GSC), which constitute a cell autonomous reservoir of aberrant cells able to initiate, maintain, and repopulate the tumor mass. Here, we report that the expression of the paracaspase mucosa-associated lymphoid tissue l (MALT1), a protease previously linked to antigen receptor-mediated NF-κB activation and B-cell lymphoma survival, inversely correlates with patient probability of survival. The knockdown of MALT1 largely impaired the expansion of patient-derived stem-like cells in vitro, and this could be recapitulated with pharmacological inhibitors, in vitro and in vivo. Blocking MALT1 protease activity increases the endo-lysosome abundance, impairs autophagic flux, and culminates in lysosomal-mediated cell death, concomitantly with mTOR inactivation and dispersion from endo-lysosomes. These findings place MALT1 as a new druggable target involved in glioblastoma and unveil ways to modulate the homeostasis of endo-lysosomes.

The clinical and mechanistic intersection of primary atopic disorders and inborn errors of growth and metabolism

Dynamic changes in metabolism have long been understood as critical for both the initiation and maintenance of innate and adaptive immune responses. A number of recent advances have clarified details of how metabolic pathways can specifically affect cellular function in immune cells. Critical to this understanding is ongoing study of the congenital disorders of glycosylation and other genetic disorders of metabolism that lead to altered immune function in humans. While there are a number of immune phenotypes associated with metabolic derangements caused by single gene disorders, several genetic mutations have begun to link discrete alterations in metabolism and growth specifically with allergic disease. This subset of primary atopic disorders is of particular interest as they illuminate how hypomorphic mutations which allow for some residual function of mutated protein products permit the "abnormal" allergic response. This review will highlight how mutations altering sugar metabolism and mTOR activation place similar constraints on T lymphocyte metabolism to engender atopy, and how alterations in JAK/STAT signaling can impair growth and cellular metabolism while concomitantly promoting allergic diseases and reactions in humans.

Graded diacylglycerol kinases α and ζ activities ensure mucosal-associated invariant T-cell development in mice

Mucosal-associated invariant T (MAIT) cells participate in both protective immunity and pathogenesis of diseases. Most murine MAIT cells express an invariant TCRVα19-Jα33 (iVα19) TCR, which triggers signals crucial for their development. However, signal pathways downstream of the iVα19TCR and their regulation in MAIT cells are unknown. Diacylglycerol (DAG) is a critical second messenger that relays the TCR signal to multiple downstream signaling cascades. DAG is terminated by DAG kinase (DGK)-mediated phosphorylation and conversion to phosphatidic acid. We have demonstrated here that downregulation of DAG caused by enhanced DGK activity impairs late-stage MAIT cell maturation in both thymus and spleen. Moreover, deficiency of DGKζ but not DGKα by itself causes modest decreases in MAIT cells, and deficiency of both DGKα and ζ results in severe reductions of MAIT cells in an autonomous manner. Our studies have revealed that DAG signaling is not only critical but also must be tightly regulated by DGKs for MAIT cell development and that both DGKα and, more prominently, DGKζ contribute to the overall DGK activity for MAIT cell development.

DAPK1 (death associated protein kinase 1) mediates mTORC1 activation and antiviral activities in CD8+ T cells

Mechanistic target of rapamycin complex 1 (mTORC1) regulates CD8⁺ T-cell differentiation and function. Despite the links between PI3K-AKT and mTORC1 activation in CD8⁺ T cells, the molecular mechanism underlying mTORC1 activation remains unclear. Here, we show that both the kinase activity and the death domain of DAPK1 are required for maximal mTOR activation and CD8⁺ T-cell function. We found that TCR-induced activation of calcineurin activates DAPK1, which subsequently interacts with TSC2 via its death domain and phosphorylates TSC2 to mediate mTORC1 activation. Furthermore, both the kinase domain and death domain of DAPK1 are required for CD8⁺ T-cell antiviral responses in an LCMV infection model. Together, our data reveal a novel mechanism of mTORC1 activation that mediates optimal CD8⁺ T-cell function and antiviral activity.

MALT1 Proteolytic Activity Suppresses Autoimmunity in a T Cell Intrinsic Manner

MALT1 is a central signaling component in innate and adaptive immunity by regulating NF-κB and other key signaling pathways in different cell types. Activities of MALT1 are mediated by its scaffold and protease functions. Because of its role in lymphocyte activation and proliferation, inhibition of MALT1 proteolytic activity is of high interest for therapeutic targeting in autoimmunity and certain lymphomas. However, recent studies showing that Malt1 protease-dead knock-in (Malt1-PD) mice suffer from autoimmune disease have somewhat tempered the initial enthusiasm. Although it has been proposed that an imbalance between immune suppressive regulatory T cells (Tregs) and activated effector CD4+ T cells plays a key role in the autoimmune phenotype of Malt1-PD mice, the specific contribution of MALT1 proteolytic activity in T cells remains unclear. Using T cell-conditional Malt1 protease-dead knock-in (Malt1-PDT) mice, we here demonstrate that MALT1 has a T cell-intrinsic role in regulating the homeostasis and function of thymic and peripheral T cells. T cell-specific ablation of MALT1 proteolytic activity phenocopies mice in which MALT1 proteolytic activity has been genetically inactivated in all cell types. The Malt1-PDT mice have a reduced number of Tregs in the thymus and periphery, although the effect in the periphery is less pronounced compared to full-body Malt1-PD mice, indicating that also other cell types may promote Treg induction in a MALT1 protease-dependent manner. Despite the difference in peripheral Treg number, both T cell-specific and full-body Malt1-PD mice develop ataxia and multi-organ inflammation to a similar extent. Furthermore, reconstitution of the full-body Malt1-PD mice with T cell-specific expression of wild-type human MALT1 eliminated all signs of autoimmunity. Together, these findings establish an important T cell-intrinsic role of MALT1 proteolytic activity in the suppression of autoimmune responses.

Gene-environment interactions in primary atopic disorders

Environmental factors modify disease presentation and severity in allergic disorders. Primary atopic disorders (PADs) are a heterogenous group of single gene disorders that lead to significant atopic and allergic disease manifestations. However, a number of these monogenic diseases have variable penetrance suggesting that gene-gene and/or gene-environment interactions could modulate the clinical phenotype. Environmental factors such as diet, the microbiome at the epithelial-environment interface, the presence and/or extent of infection, and psychologic stress can alter disease phenotypic expression of allergic diseases, and PADs provide discrete contexts in which to understand these influences. We outline how gene-environment interactions likely contribute to a variable penetrance and expressivity in PADs. Dietary modifications of both macronutrients and/or micronutrients alter T-cell metabolism and may influence effector T-cell function. The mucosal microbiome may affect local inflammation and may remotely influence regulatory elements, while psychologic stress can affect mast cell and other allergic effector cell function. Understanding gene-environment interactions in PADs can hopefully provide a foundation for interrogating gene-environment interactions to common allergic disorders, and also present opportunities for personalized interventions based on the altered pathways and environmental influences in affected individuals.

Metabolism in Immune Cell Differentiation and Function

The immune system is a central determinant of organismal health. Functional immune responses require quiescent immune cells to rapidly grow, proliferate, and acquire effector functions when they sense infectious agents or other insults. Specialized metabolic programs are critical regulators of immune responses, and alterations in immune metabolism can cause immunological disorders. There has thus been growing interest in understanding how metabolic processes control immune cell functions under normal and pathophysiological conditions. In this chapter, we summarize how metabolic programs are tuned and what the physiological consequences of metabolic reprogramming are as they relate to immune cell homeostasis, differentiation, and function.

Hypomorphic caspase activation and recruitment domain 11 (CARD11) mutations associated with diverse immunologic phenotypes with or without atopic disease

BACKGROUND

Caspase activation and recruitment domain 11 (CARD11) encodes a scaffold protein in lymphocytes that links antigen receptor engagement with downstream signaling to nuclear factor κB, c-Jun N-terminal kinase, and mechanistic target of rapamycin complex 1. Germline CARD11 mutations cause several distinct primary immune disorders in human subjects, including severe combined immune deficiency (biallelic null mutations), B-cell expansion with nuclear factor κB and T-cell anergy (heterozygous, gain-of-function mutations), and severe atopic disease (loss-of-function, heterozygous, dominant interfering mutations), which has focused attention on CARD11 mutations discovered by using whole-exome sequencing.

OBJECTIVES

We sought to determine the molecular actions of an extended allelic series of CARD11 and to characterize the expanding range of clinical phenotypes associated with heterozygous CARD11 loss-of-function alleles.

METHODS

Cell transfections and primary T-cell assays were used to evaluate signaling and function of CARD11 variants.

RESULTS

Here we report on an expanded cohort of patients harboring novel heterozygous CARD11 mutations that extend beyond atopy to include other immunologic phenotypes not previously associated with CARD11 mutations. In addition to (and sometimes excluding) severe atopy, heterozygous missense and indel mutations in CARD11 presented with immunologic phenotypes similar to those observed in signal transducer and activator of transcription 3 loss of function, dedicator of cytokinesis 8 deficiency, common variable immunodeficiency, neutropenia, and immune dysregulation, polyendocrinopathy, enteropathy, X-linked-like syndrome. Pathogenic variants exhibited dominant negative activity and were largely confined to the CARD or coiled-coil domains of the CARD11 protein.

CONCLUSION

These results illuminate a broader phenotypic spectrum associated with CARD11 mutations in human subjects and underscore the need for functional studies to demonstrate that rare gene variants encountered in expected and unexpected phenotypes must nonetheless be validated for pathogenic activity.

RNA Splicing: A New Paradigm in Host-Pathogen Interactions

RNA splicing brings diversity to the eukaryotic proteome. Different spliced variants of a gene may differ in their structure, function, localization, and stability influencing protein stoichiometry and physiological outcomes. Alternate spliced variants of different genes are known to associate with various chronic pathologies including cancer. Emerging evidence suggests precise regulation of splicing as fundamental to normal well-being. In this context, infection-induced alternative splicing has emerged as a new pivot of host function, which pathogenic microbes can alter-directly or indirectly-to tweak the host immune responses against the pathogen. The implications of these findings are vast, and although not explored much in the case of pathogenic infections, we present here examples from splicing mediated regulation of immune responses across a variety of conditions and explore how this fascinating finding brings a new paradigm to host-pathogen interactions.