Essential role for ZAP-70 in both positive and negative selection of thymocytes

The association of lipid accumulation product with inflammatory parameters and mortality: evidence from a large population-based study

Background

Obesity is closely associated with lipid metabolism, and the accumulation of lipids leads to low-level inflammation in the body, which can trigger cardiovascular disease. This study aimed to explore the association between a novel marker of lipid accumulation, the abdominal volume index (AVI), inflammatory parameters, and mortality.

Methods

This study enrolled 2,109 older adult senior citizens (aged over 60 years) with hypertension from the National Health and Nutrition Examination Survey. The primary endpoints included all-cause mortality and cardiovascular mortality, which were assessed by linking the data to the National Death Index records. Cox regression model and subgroup analysis were constructed to investigate the associations between AVI and both all-cause and cardiovascular mortality. Restricted cubic splines were employed to further explore the relationships among AVI, inflammatory parameters, and mortality. By considering inflammatory factors as mediators, we investigate the mediating effects of AVI on mortality.

Results

After a median follow-up of 69 months, there were 1,260 deaths, with 337 attributed to cardiovascular causes within the older adult population studied. In the multivariable-adjusted model, AVI was positively associated with both all-cause and cardiovascular mortality [Hazard Ratio (HR) = 1.09, 95% CI = 1.06-1.11 for all-cause mortality; HR = 1.07, 95% CI = 1.03-1.12 for cardiovascular mortality]. Kaplan-Meier survival plots indicated an overall median survival time of 144 months. Mediation analysis revealed that Systemic Inflammatory Response Index (SIRI), Monocyte-to-HDL ratio (MHR), and Neutrophil-to-Lymphocyte ratio (NLR) mediated 27.15%, 35.15%, and 16.55%, respectively, of the association between AVI and all-cause mortality.

Conclusion

AVI is positively associated with all-cause mortality in older adults with hypertension, and this association appears to be partially mediated by inflammatory parameters.

The mechanism of allosteric activation of SYK kinase derived from multiple phospho-ITAM-bound structures

Spleen tyrosine kinase (SYK) is central to adaptive and innate immune signaling. It features a regulatory region containing tandem SH2 (tSH2) domains separated by a helical "hinge" segment keeping SYK inactive by associating with the kinase domain. SYK activation is triggered when the tSH2 domains bind to a phosphorylated immunoreceptor tyrosine-based activation motif (ITAM) found on receptor tails. Past mutational studies have indicated that ITAM binding disrupts the hinge-kinase interaction, leading to SYK phosphorylation and activation. However, the mechanism of this process is unclear, as the ITAM interaction occurs far from the hinge region. We have determined crystal structures of three phospho-ITAMs in complex with the tSH2 domains, revealing a highly conserved binding mechanism. These structures, together with mutational studies and biophysical analyses, reveal that phospho-ITAM binding restricts SH2 domain movement and causes allosteric changes in the hinge region. These changes are not compatible with the association of the kinase domain, leading to kinase activation.

Is systemic inflammation a missing link between cardiometabolic index with mortality? Evidence from a large population-based study

BACKGROUND

This study sought to elucidate the associations of cardiometabolic index (CMI), as a metabolism-related index, with all-cause and cardiovascular mortality among the older population. Utilizing data from the National Health and Nutrition Examination Survey (NHANES), we further explored the potential mediating effect of inflammation within these associations.

METHODS

A cohort of 3029 participants aged over 65 years old, spanning six NHANES cycles from 2005 to 2016, was enrolled and assessed. The primary endpoints of the study included all-cause mortality and cardiovascular mortality utilizing data from National Center for Health Statistics (NCHS). Cox regression model and subgroup analysis were conducted to assess the associations of CMI with all-cause and cardiovascular mortality. The mediating effect of inflammation-related indicators including leukocyte, neutrophil, lymphocyte, systemic immune-inflammation index (SII), neutrophil to lymphocyte ratio (NLR) were evaluated to investigate the potential mechanism of the associations between CMI and mortality through mediation package in R 4.2.2.

RESULTS

The mean CMI among the enrolled participants was 0.74±0.66, with an average age of 73.28±5.50 years. After an average follow-up period of 89.20 months, there were 1,015 instances of all-cause deaths and 348 cardiovascular deaths documented. In the multivariable-adjusted model, CMI was positively related to all-cause mortality (Hazard Ratio (HR)=1.11, 95% CI=1.01-1.21). Mediation analysis indicated that leukocytes and neutrophils mediated 6.6% and 13.9% of the association of CMI with all-cause mortality.

CONCLUSION

Elevated CMI is positively associated with all-cause mortality in the older adults. The association appeared to be partially mediated through inflammatory pathways, indicating that CMI may serve as a valuable indicator for poor prognosis among the older population.

Rare Biallelic Variants Affecting the Interdomain B Region of Zeta-Chain Associated Protein Kinase 70 (ZAP70) Protein in a Sudanese Patient: Case Report

Introduction

A class of disorders known as inborn errors of immunity (IEI) is defined by a compromised or missing immune response, which increases the vulnerability to infections, immunological dysregulation, and cancer. Severe combined immunodeficiencies (SCIDs), affecting both T and B-cell function are rare but often severe diseases. In this report, we describe a 10-month-old SCID patient from Sudan with disseminated BCG infection.

Case Presentation

A 10-month-old boy whose parents were first degree relatives, presented with a six-month history of repeated chest infections and fever. Physical examination revealed a very ill-looking boy with respiratory distress dependent on oxygen, had slight abdominal distention and hepatomegaly. Investigations revealed positive polymerase chain reaction (PCR) for M. tuberculosis complex infection and low CD4+ and CD8+ cells. Genetic testing showed compound heterozygosity in trans for two variants in the Zeta-chain Associated Protein Kinase 70 (ZAP70) gene associated with autosomal recessive SCID. The patient was started on BCG-related infection treatment, intravenous immunoglobulin (IVIG) replacement and trimethoprim/sulfamethoxazole prophylaxis with an excellent response and the patient responded well to the treatment.

Conclusion

SCIDs are rare, and early management is crucial. In this case, a diagnosis of ZAP70 deficiency was based on next-generation sequencing and inhouse bioinformatic computational analysis of the ZAP70 gene, highlighting the importance of genetic testing in the workup of immunodeficiencies in low resource settings.

The complement factor H-related protein-5 (CFHR5) exacerbates pathological bone formation in ankylosing spondylitis

Ankylosing spondylitis (AS) is a chronic inflammatory disease, characterized by excessive new bone formation. We previously reported that the complement factor H-related protein-5 (CFHR5), a member of the human factor H protein family, is significantly elevated in patients with AS compared to other rheumatic diseases. However, the pathophysiological mechanism underlying new bone formation by CFHR5 is not fully understood. In this study, we revealed that CFHR5 and proinflammatory cytokines (TNF, IL-6, IL-17A, and IL-23) were elevated in the AS group compared to the HC group. Correlation analysis revealed that CFHR5 levels were not significantly associated with proinflammatory cytokines, while CFHR5 levels in AS were only positively correlated with the high CRP group. Notably, treatment with soluble CFHR5 has no effect on clinical arthritis scores and thickness at hind paw in curdlan-injected SKG, but significantly increased the ectopic bone formation at the calcaneus and tibia bones of the ankle as revealed by micro-CT image and quantification. Basal CFHR5 expression was upregulated in AS-osteoprogenitors compared to control cells. Also, treatment with CFHR5 remarkedly induced bone mineralization status of AS-osteoprogenitors during osteogenic differentiation accompanied by MMP13 expression. We provide the first evidence demonstrating that CFHR5 can exacerbate the pathological bone formation of AS. Therapeutic modulation of CFHR5 could be promising for future treatment of AS. KEY MESSAGES: Serum level of CFHR5 is elevated and positively correlated with high CRP group of AS patients. Recombinant CFHR5 protein contributes to pathological bone formation in in vivo model of AS. CFHR5 is highly expressed in AS-osteoprogenitors compared to disease control. Recombinant CFHR5 protein increased bone mineralization accompanied by MMP13 in vitro model of AS.

T-cell virtuosity in ''knowing thyself"

Major Histocompatibility Complex (MHC) I and II and the αβ T-cell antigen receptor (TCRαβ) govern fundamental traits of adaptive immunity. They form a membrane-borne ligand-receptor system weighing host proteome integrity to detect contamination by nonself proteins. MHC-I and -II exhibit the "MHC-fold", which is able to bind a large assortment of short peptides as proxies for self and nonself proteins. The ensuing varying surfaces are mandatory ligands for Ig-like TCRαβ highly mutable binding sites. Conserved molecular signatures guide TCRαβ ligand binding sites to focus on the MHC-fold (MHC-restriction) while leaving many opportunities for its most hypervariable determinants to contact the peptide. This riveting molecular strategy affords many options for binding energy compatible with specific recognition and signalling aimed to eradicated microbial pathogens and cancer cells. While the molecular foundations of αβ T-cell adaptive immunity are largely understood, uncertainty persists on how peptide-MHC binding induces the TCRαβ signals that instruct cell-fate decisions. Solving this mystery is another milestone for understanding αβ T-cells' self/nonself discrimination. Recent developments revealing the innermost links between TCRαβ structural dynamics and signalling modality should help dissipate this long-sought-after enigma.

TCR Signals Controlling Adaptive Immunity against Toxoplasma and Cancer

T cells play a crucial role in adaptive immunity by recognizing and eliminating foreign pathogens and abnormal cells such as cancer cells. T cell receptor (TCR), which is expressed on the surface of T cells, recognizes and binds to specific antigens presented by major histocompatibility complex (MHC) molecules on antigen-presenting cells (APCs). This activation process leads to the proliferation and differentiation of T cells, allowing them to carry out their specific immune response functions. This chapter outlines the TCR signaling pathways that are common to different T cell subsets, as well as the recently elucidated TCR signaling pathway specific to CD8+ T cells and its role in controlling anti-Toxoplasma and anti-tumor immunity.

A Story of Kinases and Adaptors: The Role of Lck, ZAP-70 and LAT in Switch Panel Governing T-Cell Development and Activation

Specific antigen recognition is one of the immune system's features that allows it to mount intense yet controlled responses to an infinity of potential threats. T cells play a relevant role in the host defense and the clearance of pathogens by means of the specific recognition of peptide antigens presented by antigen-presenting cells (APCs), and, to do so, they are equipped with a clonally distributed antigen receptor called the T-cell receptor (TCR). Upon the specific engagement of the TCR, multiple intracellular signals are triggered, which lead to the activation, proliferation and differentiation of T lymphocytes into effector cells. In addition, this signaling cascade also operates during T-cell development, allowing for the generation of cells that can be helpful in the defense against threats, as well as preventing the generation of autoreactive cells. Early TCR signals include phosphorylation events in which the tyrosine kinases Lck and ZAP70 are involved. The sequential activation of these kinases leads to the phosphorylation of the transmembrane adaptor LAT, which constitutes a signaling hub for the generation of a signalosome, finally resulting in T-cell activation. These early signals play a relevant role in triggering the development, activation, proliferation and apoptosis of T cells, and the negative regulation of these signals is key to avoid aberrant processes that could generate inappropriate cellular responses and disease. In this review, we will examine and discuss the roles of the tyrosine kinases Lck and ZAP70 and the membrane adaptor LAT in these cellular processes.

Combined immunodeficiency caused by pathogenic variants in the ZAP70 C-terminal SH2 domain

Introduction

ZAP-70, a protein tyrosine kinase recruited to the T cell receptor (TCR), initiates a TCR signaling cascade upon antigen stimulation. Mutations in the ZAP70 gene cause a combined immunodeficiency characterized by low or absent CD8+ T cells and nonfunctional CD4+ T cells. Most deleterious missense ZAP70 mutations in patients are located in the kinase domain but the impact of mutations in the SH2 domains, regulating ZAP-70 recruitment to the TCR, are not well understood.

Methods

Genetic analyses were performed on four patients with CD8 lymphopenia and a high resolution melting screening for ZAP70 mutations was developed. The impact of SH2 domain mutations was evaluated by biochemical and functional analyses as well as by protein modeling.

Results and discussion

Genetic characterization of an infant who presented with pneumocystis pneumonia, mycobacterial infection, and an absence of CD8 T cells revealed a novel homozygous mutation in the C-terminal SH2 domain (SH2-C) of the ZAP70 gene (c.C343T, p.R170C). A distantly related second patient was found to be compound heterozygous for the R170C variant and a 13bp deletion in the ZAP70 kinase domain. While the R170C mutant was highly expressed, there was an absence of TCR-induced proliferation, associated with significantly attenuated TCR-induced ZAP-70 phosphorylation and a lack of binding of ZAP-70 to TCR-ζ. Moreover, a homozygous ZAP-70 R192W variant was identified in 2 siblings with combined immunodeficiency and CD8 lymphopenia, confirming the pathogenicity of this mutation. Structural modeling of this region revealed the critical nature of the arginines at positions 170 and 192, in concert with R190, forming a binding pocket for the phosphorylated TCR-ζ chain. Deleterious mutations in the SH2-C domain result in attenuated ZAP-70 function and clinical manifestations of immunodeficiency.

Reactive oxygen species formation and its effect on CD4+ T cell-mediated inflammation

Reactive oxygen species (ROS) are produced both enzymatically and non-enzymatically in vivo. Physiological concentrations of ROS act as signaling molecules that participate in various physiological and pathophysiological activities and play an important role in basic metabolic functions. Diseases related to metabolic disorders may be affected by changes in redox balance. This review details the common generation pathways of intracellular ROS and discusses the damage to physiological functions when the ROS concentration is too high to reach an oxidative stress state. We also summarize the main features and energy metabolism of CD4+ T-cell activation and differentiation and the effects of ROS produced during the oxidative metabolism of CD4+ T cells. Because the current treatment for autoimmune diseases damages other immune responses and functional cells in the body, inhibiting the activation and differentiation of autoreactive T cells by targeting oxidative metabolism or ROS production without damaging systemic immune function is a promising treatment option. Therefore, exploring the relationship between T-cell energy metabolism and ROS and the T-cell differentiation process provides theoretical support for discovering effective treatments for T cell-mediated autoimmune diseases.

Construction of a T cell receptor signaling range for spontaneous development of autoimmune disease

Thymic selection and peripheral activation of conventional T (Tconv) and regulatory T (Treg) cells depend on TCR signaling, whose anomalies are causative of autoimmunity. Here, we expressed in normal mice mutated ZAP-70 molecules with different affinities for the CD3 chains, or wild type ZAP-70 at graded expression levels under tetracycline-inducible control. Both manipulations reduced TCR signaling intensity to various extents and thereby rendered those normally deleted self-reactive thymocytes to become positively selected and form a highly autoimmune TCR repertoire. The signal reduction more profoundly affected Treg development and function because their TCR signaling was further attenuated by Foxp3 that physiologically repressed the expression of TCR-proximal signaling molecules, including ZAP-70, upon TCR stimulation. Consequently, the TCR signaling intensity reduced to a critical range generated pathogenic autoimmune Tconv cells and concurrently impaired Treg development/function, leading to spontaneous occurrence of autoimmune/inflammatory diseases, such as autoimmune arthritis and inflammatory bowel disease. These results provide a general model of how altered TCR signaling evokes autoimmune disease.

Spleen tyrosine kinase mediates the γδTCR signaling required for γδT cell commitment and γδT17 differentiation

The γδT cells that produce IL-17 (γδT17 cells) play a key role in various pathophysiologic processes in host defense and homeostasis. The development of γδT cells in the thymus requires γδT cell receptor (γδTCR) signaling mediated by the spleen tyrosine kinase (Syk) family proteins, Syk and Zap70. Here, we show a critical role of Syk in the early phase of γδT cell development using mice deficient for Syk specifically in lymphoid lineage cells (Syk-conditional knockout (cKO) mice). The development of γδT cells in the Syk-cKO mice was arrested at the precursor stage where the expression of Rag genes and αβT-lineage-associated genes were retained, indicating that Syk is required for γδT-cell lineage commitment. Loss of Syk in γδT cells weakened TCR signal-induced phosphorylation of Erk and Akt, which is mandatory for the thymic development of γδT17 cells. Syk-cKO mice exhibited a loss of γδT17 cells in the thymus as well as throughout the body, and thereby are protected from γδT17-dependent psoriasis-like skin inflammation. Collectively, our results indicate that Syk is a key player in the lineage commitment of γδT cells and the priming of γδT17 cell differentiation.

Analysis of the potential association between ferroptosis and immune in hepatocellular carcinoma and their relationship with prognosis

Background

The development of targeted therapy and immunotherapy has enriched the treatment of hepatocellular carcinoma (HCC), however, have had poor or no reponse, or even no response. Previous research suggested that ferroptosis and tumor immune microenvironment (TIME) may have a fundamental impact on efficacy during HCC immunotherapy and targeted therapy. Therefore, there is a clinical need to develop a signature that categorizes HCC patients in order to make more accurate clinical decisions.

Methods

Clinical data and gene expression data of HCC patients were obtained from The Cancer Genome Atlas (TCGA) portal and International Cancer Genome Consortium (ICGC) portal. To identify ferroptosis-related immune-related genes (ferroptosis-related IRGs), Pearson correlation analysis was conducted. The ferroptosis-related IRGs prognostic signature (FIPS) was constructed using Univariate Cox and LASSO Cox algorithms. The predictive effectiveness of FIPS was evaluated using Receiver Operating Characteristic (ROC) curves and survivorship curve. The correlation ship between FIPS and TIME was evaluated using single-sample Gene Set Enrichment Analysis (ssGSEA) and CIBERSORT. The relationship between FIPS and immunotherapy responsiveness was evaluated using immunophenoscore. The expression level of 10 ferroptosis-related IRGs in normal liver tissues and HCC tissues was compared using immunohistochemistry. Finally, we established a nomogram (based on FIPS, TNM stage, and age) for clinical application.

Results

The FIPS was established with ten ferroptosis-related IRGs. The high-FIPS subgroup showed a poor clinical prognosis and an obviously higher proportion of HCC patients with advanced TNM stage, high WHO grade and high alpha fetoprotein(AFP) value. Analysis of TIME indicated that patients in the high-FIPS subgroup may be in immunosuppressed state. Meanwhile, we found that ferroptosis may be inhibited in the high-FIPS subgroup and this subgroup may be impervious to immunotherapy and sorafenib.

Conclusion

We constructed a novel potential prognostic signature for HCC patients that predicts overall survival, ferroptosis and immune status, sorafenib sensitivity, and immunotherapy responsiveness.

Revelations in Thymic Epithelial Cell Biology and Heterogeneity from Single-Cell RNA Sequencing and Lineage Tracing Methodologies

Thymic epithelial cells (TECs) make up the thymic microenvironments that support the generation of a functionally competent and self-tolerant T-cell repertoire. Cortical (c)TECs, present in the cortex, are essential for early thymocyte development including selection of thymocytes expressing functional TCRs (positive selection). Medullary (m)TECs, located in the medulla, play a key role in late thymocyte development, including depletion of self-reactive T cells (negative selection) and selection of regulatory T cells. In recent years, transcriptomic analysis by single-cell (sc)RNA sequencing (Seq) has revealed TEC heterogeneity previously masked by population-level RNA-Seq or phenotypic studies. We summarize the discoveries made possible by scRNA-Seq, including the identification of novel mTEC subsets, advances in understanding mTEC promiscuous gene expression, and TEC alterations from embryonic to adult stages. Whereas pseudotime analyses of scRNA-Seq data can suggest relationships between TEC subsets, experimental methods such as lineage tracing and reaggregate thymic organ culture (RTOC) are required to test these hypotheses. Lineage tracing - namely, of β5t or Aire expressing cells - has exposed progenitor and parent-daughter cellular relationships within TEC.

Cyclophilin A associates with and regulates the activity of ZAP70 in TCR/CD3-stimulated T cells

The ZAP70 protein tyrosine kinase (PTK) couples stimulated T cell antigen receptors (TCRs) to their downstream signal transduction pathways and is sine qua non for T cell activation and differentiation. TCR engagement leads to activation-induced post-translational modifications of ZAP70, predominantly by kinases, which modulate its conformation, leading to activation of its catalytic domain. Here, we demonstrate that ZAP70 in TCR/CD3-activated mouse spleen and thymus cells, as well as human Jurkat T cells, is regulated by the peptidyl-prolyl cis-trans isomerase (PPIase), cyclophilin A (CypA) and that this regulation is abrogated by cyclosporin A (CsA), a CypA inhibitor. We found that TCR crosslinking promoted a rapid and transient, Lck-dependent association of CypA with the interdomain B region, at the ZAP70 regulatory domain. CsA inhibited CypA binding to ZAP70 and prevented the colocalization of CypA and ZAP70 at the cell membrane. In addition, imaging analyses of antigen-specific T cells stimulated by MHC-restricted antigen-fed antigen-presenting cells revealed the recruitment of ZAP70-bound CypA to the immunological synapse. Enzymatically active CypA downregulated the catalytic activity of ZAP70 in vitro, an effect that was reversed by CsA in TCR/CD3-activated normal T cells but not in CypA-deficient T cells, and further confirmed in vivo by FRET-based studies. We suggest that CypA plays a role in determining the activity of ZAP70 in TCR-engaged T cells and impact on T cell activation by intervening with the activity of multiple downstream effector molecules.

Spatial requirements for ITAM signaling in an intracellular natural killer cell model membrane

FcγRIIIa-FcεRIγ complexes, upon stimulation by antibodies, cluster to initiate intracellular signaling and activate natural killer (NK) cells. Intracellular signaling involves Lck phosphorylation of ITAMs of each monomer of a FcεRIγ homodimer in a FcγRIIIa-FcεRIγ complex and subsequent binding of two phosphotyrosines (pY) in tandem by a Syk family kinase. However, how FcR clustering triggers ITAM signaling is not resolved. Molecular modeling and dynamics (MD) simulations are applied to generate ensembles of structures of the FcγRIIIa and FcεRIγ homodimeric cytoplasmic tails of FcγRIIIa-FcεRIγ complexes based on the transmembrane helices and cytoplasmic tails spaced 120, 80, and 50 Å apart to model different extents of clustering. Site-identification by ligand competitive saturation method with Monte Carlo sampling (SILCS-MC) is used to model how Lck could phosphorylate a diversity of ITAM conformations. At 80 Å separation between FcγRIIIa-FcεRIγ complexes, Lck can perform multiple phosphorylations on individual and multiple ITAMs across complexes, including potential sequential phosphorylation events. Syk may then potentially bind the two pYs within a single ITAM in tandem in isolated FcγRIIIa-FcεRIγ complexes, as observed in CD3ε and ζ chains of T cell receptors by the Syk family kinase ZAP-70. In addition, at 50 Å separation between complexes, unique to natural killer cells over T cells, Syk could potentially bind in tandem to pYs in different ITAMs across FcγRIIIa-FcεRIγ complexes. Thus, we predict that an ensemble of spatial orientations of the ITAMS of FcγRIIIa-FcεRIγ complexes that occur upon clustering lead to ITAM phosphorylation by Lck and subsequent Syk activity thereby facilitating downstream signaling.

A Cysteine Residue within the Kinase Domain of Zap70 Regulates Lck Activity and Proximal TCR Signaling

Alterations in both the expression and function of the non-receptor tyrosine kinase Zap70 are associated with numerous human diseases including immunodeficiency, autoimmunity, and leukemia. Zap70 propagates the TCR signal by phosphorylating two important adaptor molecules, LAT and SLP76, which orchestrate the assembly of the signaling complex, leading to the activation of PLCγ1 and further downstream pathways. These events are crucial to drive T-cell development and T-cell activation. Recently, it has been proposed that C564, located in the kinase domain of Zap70, is palmitoylated. A non-palmitoylable C564R Zap70 mutant, which has been reported in a patient suffering from immunodeficiency, is incapable of propagating TCR signaling and activating T cells. The lack of palmitoylation was suggested as the cause of this human disease. Here, we confirm that Zap70^C564R is signaling defective, but surprisingly, the defective Zap70 function does not appear to be due to a loss in palmitoylation. We engineered a C564A mutant of Zap70 which, similarly to Zap70^C564R, is non-palmitoylatable. However, this mutant was capable of propagating TCR signaling. Moreover, Zap70^C564A enhanced the activity of Lck and increased its proximity to the TCR. Accordingly, Zap70-deficient P116 T cells expressing Zap70^C564A displayed the hyperphosphorylation of TCR-ζ and Zap70 (Y319), two well-known Lck substrates. Collectively, these data indicate that C564 is important for the regulation of Lck activity and proximal TCR signaling, but not for the palmitoylation of Zap70.

The RAG1 Ubiquitin Ligase Domain Stimulates Recombination of TCRβ and TCRα Genes and Influences Development of αβ T Cell Lineages

RAG1/RAG2 (RAG) endonuclease-mediated assembly of diverse lymphocyte Ag receptor genes by V(D)J recombination is critical for the development and immune function of T and B cells. The RAG1 protein contains a ubiquitin ligase domain that stabilizes RAG1 and stimulates RAG endonuclease activity in vitro. We report in this study that mice with a mutation that inactivates the Rag1 ubiquitin ligase in vitro exhibit decreased rearrangements and altered repertoires of TCRβ and TCRα genes in thymocytes and impaired thymocyte developmental transitions that require the assembly and selection of functional TCRβ and/or TCRα genes. These Rag1 mutant mice present diminished positive selection and superantigen-mediated negative selection of conventional αβ T cells, decreased genesis of invariant NK T lineage αβ T cells, and mature CD4+ αβ T cells with elevated autoimmune potential. Our findings reveal that the Rag1 ubiquitin ligase domain functions in vivo to stimulate TCRβ and TCRα gene recombination and influence differentiation of αβ T lineage cells, thereby establishing replete diversity of αβ TCRs and populations of αβ T cells while restraining generation of potentially autoreactive conventional αβ T cells.

RNA m6A demethylase ALKBH5 regulates the development of γδ T cells

γδ T cells are an abundant T cell population at the mucosa and are important in providing immune surveillance as well as maintaining tissue homeostasis. However, despite γδ T cells' origin in the thymus, detailed mechanisms regulating γδ T cell development remain poorly understood. N⁶-methyladenosine (m⁶A) represents one of the most common posttranscriptional modifications of messenger RNA (mRNA) in mammalian cells, but whether it plays a role in γδ T cell biology is still unclear. Here, we show that depletion of the m⁶A demethylase ALKBH5 in lymphocytes specifically induces an expansion of γδ T cells, which confers enhanced protection against gastrointestinal Salmonella typhimurium infection. Mechanistically, loss of ALKBH5 favors the development of γδ T cell precursors by increasing the abundance of m⁶A RNA modification in thymocytes, which further reduces the expression of several target genes including Notch signaling components Jagged1 and Notch2. As a result, impairment of Jagged1/Notch2 signaling contributes to enhanced proliferation and differentiation of γδ T cell precursors, leading to an expanded mature γδ T cell repertoire. Taken together, our results indicate a checkpoint role of ALKBH5 and m⁶A modification in the regulation of γδ T cell early development.

An evolutionary divergent thermodynamic brake in ZAP-70 fine-tunes the kinetic proofreading in T cells

T cell signaling starts with assembling several tyrosine kinases and adaptor proteins to the T cell receptor (TCR), following the antigen-binding to the TCR. The stability of the TCR-antigen complex and the delay between the recruitment and activation of each kinase determines the T cell response. Integration of such delays constitutes a kinetic proofreading mechanism to regulate T cell response to the antigen binding. However, the mechanism of these delays is not fully understood. Combining biochemical experiments and kinetic modelling, here we report a thermodynamic brake in the regulatory module of the tyrosine kinase ZAP-70, which determines the ligand selectivity, and may delay the ZAP-70 activation upon antigen binding to TCR. The regulatory module of ZAP-70 comprises of a tandem SH2 (tSH2) domain that binds to its ligand, doubly-phosphorylated ITAM peptide (ITAM-Y2P), in two kinetic steps: a fast step and a slow step. We show the initial encounter complex formation between the ITAM-Y2P and tSH2 domain follows a fast-kinetic step, whereas the conformational transition to the holo-state follows a slow-kinetic step. We further observed a thermodynamic penalty imposed during the second phosphate-binding event reduces the rate of structural transition to the holo-state. Phylogenetic analysis revealed the evolution of the thermodynamic brake coincides with the divergence of the adaptive immune system to the cell-mediated and humoral responses. In addition, the paralogous kinase Syk expressed in B cells does not possess such a functional thermodynamic brake, which may explain the higher basal activation and lack of ligand selectivity in Syk.

Negative Regulation of Zap70 by Lck Forms the Mechanistic Basis of Differential Expression in CD4 and CD8 T Cells

Lck and Zap70, two non-receptor tyrosine kinases, play a crucial role in the regulation of membrane proximal TCR signaling critical for thymic selection, CD4/CD8 lineage choice and mature T cell function. Signal initiation upon TCR/CD3 and peptide/MHC interaction induces Lck-mediated phosphorylation of CD3 ITAMs. This is necessary for Zap70 recruitment and its phosphorylation by Lck leading to full Zap70 activation. In its native state Zap70 maintains a closed conformation creating an auto-inhibitory loop, which is relieved by Lck-mediated phosphorylation of Y315/Y319. Zap70 is differentially expressed in thymic subsets and mature T cells with CD8 T cells expressing the highest amount compared to CD4 T cells. However, the mechanistic basis of differential Zap70 expression in thymic subsets and mature T cells is not well understood. Here, we show that Zap70 is degraded relatively faster in DP and mature CD4 T cells compared to CD8 T cells, and inversely correlated with relative level of activated Zap70. Importantly, we found that Zap70 expression is negatively regulated by Lck activity: augmented Lck activity resulting in severe diminution in total Zap70. Moreover, Lck-mediated phosphorylation of Y315/Y319 was essential for Zap70 degradation. Together, these data shed light on the underlying mechanism of Lck-mediated differential modulation of Zap70 expression in thymic subsets and mature T cells.

STAP-2 Is a Novel Positive Regulator of TCR-Proximal Signals

TCR ligation with an Ag presented on MHC molecules promotes T cell activation, leading to the selection, differentiation, and proliferation of T cells and cytokine production. These immunological events are optimally arranged to provide appropriate responses against a variety of pathogens. We here propose signal-transducing adaptor protein-2 (STAP-2) as a new positive regulator of TCR signaling. STAP-2-deficient T cells showed reduced, whereas STAP-2-overexpressing T cells showed enhanced, TCR-mediated signaling and downstream IL-2 production. For the mechanisms, STAP-2 associated with TCR-proximal CD3ζ immunoreceptor tyrosine activation motifs and phosphorylated LCK, resulting in enhancement of their binding after TCR stimulation. In parallel, STAP-2 expression is required for full activation of downstream TCR signaling. Importantly, STAP-2-deficient mice exhibited slight phenotypes of CD4⁺ T-cell-mediated inflammatory diseases, such as experimental autoimmune encephalomyelitis, whereas STAP-2-overexpressing transgenic mice showed severe phenotypes of these diseases. Together, STAP-2 is an adaptor protein to enhance TCR signaling; therefore, manipulating STAP-2 will have an ability to improve the treatment of patients with autoimmune diseases as well as the chimeric Ag receptor T cell therapy.

Signaling Crosstalks Drive Generation and Regeneration of the Thymus

Optimal recovery of immune competence after periods of hematopoietic insults or stress is crucial to re-establish patient response to vaccines, pathogens and tumor antigens. This is particularly relevant for patients receiving high doses of chemotherapy or radiotherapy, who experience prolonged periods of lymphopenia, which can be associated with an increased risk of infections, malignant relapse, and adverse clinical outcome. While the thymus represents the primary organ responsible for the generation of a diverse pool of T cells, its function is profoundly impaired by a range of acute insults (including those caused by cytoreductive chemo/radiation therapy, infections and graft-versus-host disease) and by the chronic physiological deterioration associated with aging. Impaired thymic function increases the risk of infections and tumor antigen escape due to a restriction in T-cell receptor diversity and suboptimal immune response. Therapeutic approaches that can promote the renewal of the thymus have the potential to restore immune competence in patients. Previous work has documented the importance of the crosstalk between thymocytes and thymic epithelial cells in establishing correct architecture and function of thymic epithelium. This crosstalk is relevant not only during thymus organogenesis, but also to promote the recovery of its function after injuries. In this review, we will analyze the signals involved in the crosstalk between TECs and hematopoietic cells. We will focus in particular on how signals from T-cells can regulate TEC function and discuss the relevance of these pathways in restoring thymic function and T-cell immunity in experimental models, as well as in the clinical setting.

SYK and ZAP70 kinases in autoimmunity and lymphoid malignancies

SYK and ZAP70 nonreceptor tyrosine kinases serve essential roles in initiating B-cell receptor (BCR) and T-cell receptor (TCR) signaling in B- and T-lymphocytes, respectively. Despite their structural and functional similarity, expression of SYK and ZAP70 is strictly separated during B- and T-lymphocyte development, the reason for which was not known. Aberrant co-expression of ZAP70 with SYK was first identified in B-cell chronic lymphocytic leukemia (CLL) and is considered a biomarker of aggressive disease and poor clinical outcomes. We recently found that aberrant ZAP70 co-expression not only functions as an oncogenic driver in CLL but also in various other B-cell malignancies, including acute lymphoblastic leukemia (B-ALL) and mantle cell lymphoma. Thereby, aberrantly expressed ZAP70 redirects SYK and BCR-downstream signaling from NFAT towards activation of the PI3K-pathway. In the sole presence of SYK, pathological BCR-signaling in autoreactive or premalignant cells induces NFAT-activation and NFAT-dependent anergy and negative selection. In contrast, negative selection of pathological B-cells is subverted when ZAP70 diverts SYK from activation of NFAT towards tonic PI3K-signaling, which promotes survival instead of cell death. We discuss here how both B-cell malignancies and autoimmune diseases frequently evolve to harness this mechanism, highlighting the importance of developmental separation of the two kinases as an essential safeguard.

Vγ5Vδ1 TCR signaling is required to different extents for embryonic versus postnatal development of DETCs

δγ T cells expressing Vγ5Vδ1 TCR originally develop in the embryonic thymus and migrate to the epidermis, forming dendritic epidermal T cells (DETCs) throughout life. It is thought that a TCR signal is essential for their development; e.g., lack of TCR signal-transducer ZAP70 significantly decreases DETC numbers. On the other hand, lack of ZAP70 does not affect Vγ5Vδ1 + T cells in the embryonic thymus; thus, the involvement of TCR signaling remains elusive. Here, we used SKG mice with attenuated TCR signaling rather than gene-knockout mice. In SKG mice, Vγ5 + T cells showed a marked decrease (10% of wild-type) in adult epidermis; however, there was just a moderate decrease (50% of wild-type) in the embryonic thymus. In early postnatal epidermis in SKG mice, substantial numbers of Vγ5 + T cells were observed (50% of wild-type). Their activation markers including CD122, a component of the IL-15 receptor indispensable for DETC proliferation, were comparable to those of WT. However, the Vγ5 + T cells in SKG mice did not proliferate and form DETCs thereafter. Furthermore, in SKG/+ mice, the number of thymic Vγ5Vδ1 + T cells increased, compared to SKG mice; however, the number of DETCs remained significantly lower than in WT, similar to SKG mice. Our results suggest that signaling via Vγ5Vδ1 TCR is indispensable for DETC development, with distinct contributions to embryonic development and postnatal proliferation.

Fanconi Anemia Pathway Genes Advance Cervical Cancer via Immune Regulation and Cell Adhesion

Fanconi anemia (FA) pathway is a typical and multienzyme-regulated DNA damage repairer that influences the occurrence and development of disease including cancers. Few comprehensive analyses were reported about the role of FA-related genes (FARGs) and their prognostic values in cancers. In this study, a comprehensive pan-cancer analysis on 79 FARGs was performed. According to the correlation analyses between HPV integration sites and FARGs, we found that FARGs played specific and critical roles in HPV-related cancers, especially in cervical cancer (CC). Based on this, a FARGs-associated prognostic risk score (FPS) model was constructed, and subsequently a nomogram model containing the FPS was developed with a good accuracy for CC overall survival (OS) and recurrence-free survival (RFS) outcome prediction. We also used the similar expression pattern of FARGs by consensus clustering analysis to separate the patients into three subgroups that exhibited significant differential OS but not RFS. Moreover, differential expressed genes (DEGs) between the two risk groups or three clusters were identified and immune pathways as well as cell adhesion processes were determined by functional enrichment analysis. Results indicated that FARGs might promote occurrence and development of CC by regulating the immune cells' infiltration and cell adhesion. In addition, through the machine learning models containing decision tree, random forest, naïve bayes, and support vector machine models, screening of important variables on CC prognosis, we finally determined that ZBTB32 and CENPS were the main elements affecting CC OS, while PALB2 and BRCA2 were for RFS. Kaplan-Meier analysis revealed that bivariate prediction of CC outcome was reliable. Our study systematically analyzed the prognostic prediction values of FARGs and demonstrated their potential mechanism in CC aggressiveness. Results provided perspective in FA pathway-associated modification and theoretical basis for CC clinical treatments.

ZAP70 activation is an early event of T cell immunity that involved in the anti-bacterial adaptive immune response of Nile tilapia

ZAP70 is essential for initiating the early events of T-cell antigen receptor (TCR) signaling cascade to ensure proper T cell activation and function. However, whether this molecule takes part in the T cell immune response of early vertebrates remains unclear. In the present study, using a teleost model Nile tilapia (Oreochromis niloticus), we investigated the potential involvement of ZAP70 in the T cell activation and adaptive immunity of fish species. Both primary and tertiary structures of O. niloticus ZAP70 (On-ZAP70) are highly conserved with those from other vertebrates. On-ZAP70 protein was widely expressed in lymphoid tissues, and with the highest level in thymus. Once Nile tilapia was infected by Aeromonas hydrophila, mRNA of On-ZAP70 in spleen lymphocytes was induced on day 5 and 8 after infection; meanwhile, phosphorylation of On-ZAP70 was also enhanced, suggesting that On-ZAP70 potentially participated in primary adaptive immune response of Nile tilapia. Furthermore, the frequency of ZAP70 positive lymphocytes was increased during the anti-bacterial adaptive immune response. More importantly, when spleen lymphocytes were activated by T cell specific mitogen PHA, a dramatical augment of On-ZAP70 could be observed at transcription, phosphorylation and cellular level, indicating the involvement of this molecule in T cells activation of Nile tilapia. Altogether, our results demonstrated that ZAP70 activation is an early event of T cell immunity that involved in the anti-bacterial adaptive immune response of Nile tilapia, and thus provided a new evidence to understand the evolution of the lymphocyte-mediated adaptive immunity.

A rapid CRISPR competitive assay for in vitro and in vivo discovery of potential drug targets affecting the hematopoietic system

CRISPR/Cas9 can be used as an experimental tool to inactivate genes in cells. However, a CRISPR-targeted cell population will not show a uniform genotype of the targeted gene. Instead, a mix of genotypes is generated - from wild type to different forms of insertions and deletions. Such mixed genotypes complicate analysis of the role of the targeted gene in the studied cell population. Here, we present a rapid and universal experimental approach to functionally analyze a CRISPR-targeted cell population that does not involve generating clonal lines. As a simple readout, we leverage the CRISPR-induced genetic heterogeneity and use sequencing to identify how different genotypes are enriched or depleted in relation to the studied cellular behavior or phenotype. The approach uses standard PCR, Sanger sequencing, and a simple sequence deconvoluting software, enabling laboratories without specific in-depth experience to perform these experiments. As proof of principle, we present examples studying various aspects related to hematopoietic cells (T cell development in vivo and activation in vitro, differentiation of macrophages and dendritic cells, as well as a leukemia-like phenotype induced by overexpressing a proto-oncogene). In conclusion, we present a rapid experimental approach to identify potential drug targets related to mature immune cells, as well as normal and malignant hematopoiesis.

Ssu72 phosphatase directly binds to ZAP-70, thereby providing fine-tuning of TCR signaling and preventing spontaneous inflammation

ZAP-70 is required for the initiation of T cell receptor (TCR) signaling, and Ssu72 is a phosphatase that regulates RNA polymerase II activity in the nucleus. However, the mechanism by which ZAP-70 regulates the fine-tuning of TCR signaling remains elusive. Here, we found that Ssu72 contributed to the fine-tuning of TCR signaling by acting as tyrosine phosphatase for ZAP-70. Affinity purification-mass spectrometry and an in vitro assay demonstrated specific interaction between Ssu72 and ZAP-70 in T cells. Upon TCR stimulation, Ssu72-deficient T cells increased the phosphorylation of ZAP-70 and downstream molecules and exhibited hyperresponsiveness, which was restored by reducing ZAP-70 phosphorylation. In vitro assay demonstrated that recombinant Ssu72 reduced tyrosine phosphorylation of ZAP-70 via phosphatase activity. Cd4-CreSsu72 ^fl/fl mice showed a defect in the thymic development of invariant natural killer T cells and reductions in CD4⁺ and CD8⁺ T cell numbers in the periphery but more CD44^hiCD62L^lo memory T cells and fewer CD44^loCD62L^hi naïve T cells, compared with wild-type mice. Furthermore, Cd4-CreSsu72 ^fl/fl mice developed spontaneous inflammation at 6 mo. In conclusion, Ssu72 phosphatase regulates the fine-tuning of TCR signaling by binding to ZAP-70 and regulating its tyrosine phosphorylation, thereby preventing spontaneous inflammation.

Lymphotoxin: from the physiology to the regeneration of the thymic function

The members of the Tumor Necrosis Factor (TNF) superfamily, the ligand lymphotoxin α1β2 (LTα1β2) and its unique receptor lymphotoxin β receptor (LTβR), play a pivotal role in the establishment and regulation of the immune system by allowing a tight communication between lymphocytes and stromal cells. Recent advances using transgenic mice harboring a specific deletion of the Ltbr gene in distinct stromal cells have revealed important roles for LTβR signaling in the thymic function that ensures the generation of a diverse and self-tolerant T-cell repertoire. In this review, we summarize our current knowledge on this signaling axis in the thymic homing of lymphoid progenitors and peripheral antigen-presenting cells, the trafficking and egress of thymocytes, the differentiation of medullary thymic epithelial cells, and the establishment of central tolerance. We also highlight the importance of LTα1β2/LTβR axis in controlling the recovery of the thymic function after myeloablative conditioning regimen, opening novel perspectives in regenerative medicine.

Developmental partitioning of SYK and ZAP70 prevents autoimmunity and cancer

Even though SYK and ZAP70 kinases share high sequence homology and serve analogous functions, their expression in B and T cells is strictly segregated throughout evolution. Here, we identified aberrant ZAP70 expression as a common feature in a broad range of B cell malignancies. We validated SYK as the kinase that sets the thresholds for negative selection of autoreactive and premalignant clones. When aberrantly expressed in B cells, ZAP70 competes with SYK at the BCR signalosome and redirects SYK from negative selection to tonic PI3K signaling, thereby promoting B cell survival. In genetic mouse models for B-ALL and B-CLL, conditional expression of Zap70 accelerated disease onset, while genetic deletion impaired malignant transformation. Inducible activation of Zap70 during B cell development compromised negative selection of autoreactive B cells, resulting in pervasive autoantibody production. Strict segregation of the two kinases is critical for normal B cell selection and represents a central safeguard against the development of autoimmune disease and B cell malignancies.

Uncovering a novel role of PLCβ4 in selectively mediating TCR signaling in CD8+ but not CD4+ T cells

Because of their common signaling molecules, the main T cell receptor (TCR) signaling cascades in CD4⁺ and CD8⁺ T cells are considered qualitatively identical. Herein, we show that TCR signaling in CD8⁺ T cells is qualitatively different from that in CD4⁺ T cells, since CD8α ignites another cardinal signaling cascade involving phospholipase C β4 (PLCβ4). TCR-mediated responses were severely impaired in PLCβ4-deficient CD8⁺ T cells, whereas those in CD4⁺ T cells were intact. PLCβ4-deficient CD8⁺ T cells showed perturbed activation of peripheral TCR signaling pathways downstream of IP₃ generation. Binding of PLCβ4 to the cytoplasmic tail of CD8α was important for CD8⁺ T cell activation. Furthermore, GNAQ interacted with PLCβ4, mediated double phosphorylation on threonine 886 and serine 890 positions of PLCβ4, and activated CD8⁺ T cells in a PLCβ4-dependent fashion. PLCβ4-deficient mice exhibited defective antiparasitic host defense and antitumor immune responses. Altogether, PLCβ4 differentiates TCR signaling in CD4⁺ and CD8⁺ T cells and selectively promotes CD8⁺ T cell–dependent adaptive immunity.

Redox sensor NPGPx restrains ZAP70 activity and modulates T cell homeostasis

Emerging evidences implicate the contribution of ROS to T cell activation and signaling. The tyrosine kinase, ζ-chain-associated protein of 70 kDa (ZAP70), is essential for T cell development and activation. However, it remains elusive whether a direct redox regulation affects ZAP70 activity upon TCR stimulation. Here, we show that deficiency of non-selenocysteine containing phospholipid hydroperoxide glutathione peroxidase (NPGPx), a redox sensor, results in T cell hyperproliferation and elevated cytokine productions. T cell-specific NPGPx-knockout mice reveal enhanced T-dependent humoral responses and are susceptible to experimental autoimmune encephalomyelitis (EAE). Through proteomic approaches, ZAP70 is identified as the key interacting protein of NPGPx through disulfide bonding. NPGPx is activated by ROS generated from TCR stimulation, and modulates ZAP70 activity through redox switching to reduce ZAP70 recruitment to TCR/CD3 complex in membrane lipid raft, therefore subduing TCR responses. These results reveal a delicate redox mechanism that NPGPx serves as a modulator to curb ZAP70 functions in maintaining T cell homeostasis.

A disease-associated mutation that weakens ZAP70 autoinhibition enhances responses to weak and self-ligands

The cytoplasmic kinase ZAP70 is critical for T cell antigen receptor (TCR) signaling. The R360P mutation in ZAP70 is responsible for an early-onset familial autoimmune syndrome. The structural location and biochemical signaling effects of the R360P mutation are consistent with weakening of the autoinhibitory conformation of ZAP70. Mice with a ZAP70 R360P mutation and polyclonal TCR repertoires exhibited relatively normal T cell development but showed evidence of increased signaling. In addition, the R360P mutation resulted in enhanced follicular helper T cell expansion after LCMV infection. To eliminate the possibility of a TCR repertoire shift, the OTI transgenic TCR was introduced into R360P mice, which resulted in enhanced T cell responses to weaker stimuli, including weak agonists and a self-peptide. These observations suggest that disruption of ZAP70 autoinhibition by the R360P mutation enables increased mature T cell sensitivity to self-antigens that would normally be ignored by wild-type T cells, a mechanism that may contribute to the break of tolerance in human patients with R360P mutation.

An allosteric hot spot in the tandem-SH2 domain of ZAP-70 regulates T-cell signaling

T-cell receptor (TCR) signaling is initiated by recruiting ZAP-70 to the cytosolic part of TCR. ZAP-70, a non-receptor tyrosine kinase, is composed of an N-terminal tandem SH2 (tSH2) domain connected to the C-terminal kinase domain. The ZAP-70 is recruited to the membrane through binding of tSH2 domain and the doubly phosphorylated ITAM motifs of CD3 chains in the TCR complex. Our results show that the tSH2 domain undergoes a biphasic structural transition while binding to the doubly phosphorylated ITAM-ζ1 peptide. The C-terminal SH2 domain binds first to the phosphotyrosine residue of ITAM peptide to form an encounter complex leading to subsequent binding of second phosphotyrosine residue to the N-SH2 domain. We decipher a network of noncovalent interactions that allosterically couple the two SH2 domains during binding to doubly phosphorylated ITAMs. Mutation in the allosteric network residues, for example, W165C, uncouples the formation of encounter complex to the subsequent ITAM binding thus explaining the altered recruitment of ZAP-70 to the plasma membrane causing autoimmune arthritis in mice. The proposed mechanism of allosteric coupling is unique to ZAP-70, which is fundamentally different from Syk, a close homolog of ZAP-70 expressed in B-cells.

Postnatal Involution and Counter-Involution of the Thymus

Thymus involution occurs in all vertebrates. It is thought to impact on immune responses in the aged, and in other clinical circumstances such as bone marrow transplantation. Determinants of thymus growth and size are beginning to be identified. Ectopic expression of factors like cyclin D1 and Myc in thymic epithelial cells (TEC)s results in considerable increase in thymus size. These models provide useful experimental tools that allow thymus function to be understood. In future, understanding TEC-specific controllers of growth will provide new approaches to thymus regeneration.

Cofilin1-driven actin dynamics controls migration of thymocytes and is essential for positive selection in the thymus

Actin dynamics is essential for T-cell development. We show here that cofilin1 is the key molecule for controlling actin filament turnover in this process. Mice with specific depletion of cofilin1 in thymocytes showed increased steady-state levels of actin filaments, and associated alterations in the pattern of thymocyte migration and adhesion. Our data suggest that cofilin1 is controlling oscillatory F-actin changes, a parameter that influences the migration pattern in a 3-D environment. In a collagen matrix, cofilin1 controls the speed and resting intervals of migrating thymocytes. Cofilin1 was not involved in thymocyte proliferation, cell survival, apoptosis or surface receptor trafficking. However, in cofilin1 mutant mice, impaired adhesion and migration resulted in a specific block of thymocyte differentiation from CD4/CD8 double-positive thymocytes towards CD4 and CD8 single-positive cells. Our data suggest that tuning of the dwelling time of thymocytes in the thymic niches is tightly controlled by cofilin1 and essential for positive selection during T-cell differentiation. We describe a novel role of cofilin1 in the physiological context of migration-dependent cell differentiation.

Plasma membrane sphingomyelin modulates thymocyte development by inhibiting TCR-induced apoptosis

Sphingomyelin (SM) in combination with cholesterol forms specialized membrane lipid microdomains in which specific receptors and signaling molecules are localized or recruited to mediate intracellular signaling. SM-microdomain levels in mouse thymus were low in the early CD4+CD8+ double-positive (DP) stage prior to thymic selection and increased >10-fold during late selection. T-cell receptor (TCR) signal strength is a key factor determining whether DP thymocytes undergo positive or negative selection. We examined the role of SM-microdomains in thymocyte development and related TCR signaling, using SM synthase 1 (SMS1)-deficient (SMS1-/-) mice which display low SM expression in all thymocyte populations. SMS1 deficiency caused reduced cell numbers after late DP stages in TCR transgenic models. TCR-dependent apoptosis induced by anti-CD3 treatment was enhanced in SMS1-/- DP thymocytes both in vivo and in vitro. SMS1-/- DP thymocytes, relative to controls, showed increased phosphorylation of TCR-proximal kinase ZAP-70 and increased expression of Bim and Nur77 proteins involved in negative selection following TCR stimulation. Addition of SM to cultured normal DP thymocytes led to greatly increased surface expression of SM-microdomains, with associated reduction of TCR signaling and TCR-induced apoptosis. Our findings indicate that SM-microdomains are increased in late DP stages, function as negative regulators of TCR signaling and modulate the efficiency of TCR-proximal signaling to promote thymic selection events leading to subsequent developmental stages.

Impaired T cell receptor signaling and development of T cell-mediated autoimmune arthritis

Mutations of the genes encoding T-cell receptor (TCR)-proximal signaling molecules, such as ZAP-70, can be causative of immunological diseases ranging from T-cell immunodeficiency to T-cell-mediated autoimmune disease. For example, SKG mice, which carry a hypomorphic point mutation of the Zap-70 gene, spontaneously develop T-cell-mediated autoimmune arthritis immunopathologically similar to human rheumatoid arthritis (RA). The Zap-70 mutation alters the sensitivity of developing T cells to thymic positive/negative selection by self-peptides/MHC complexes, shifting self-reactive TCR repertoire to include a dominant arthritogenic specificity and also affecting thymic development and function of autoimmune suppressive regulatory T (Treg) cells. Polyclonal self-reactive T cells, including potentially arthritogenic T cells, thus produced by the thymus recognize self-peptide/MHC complexes on antigen-presenting cells (APCs) in the periphery and stimulate them to produce cytokines including IL-6 to drive the arthritogenic T cells to differentiate into arthritogenic T-helper 17 (Th17) cells. Insufficient Treg suppression or activation of APCs via microbial and other environmental stimuli evokes arthritis by activating granulocyte-macrophage colony-stimulating factor-secreting effector Th17 cells, mediating chronic bone-destructive joint inflammation by activating myeloid cells, innate lymphoid cells, and synoviocytes in the joint. These findings obtained from the study of SKG mouse arthritis are instrumental in understanding how arthritogenic T cells are produced, become activated, and differentiate into effector T cells mediating arthritis, and may help devising therapeutic measures targeting autoimmune pathogenic Th17 cells or autoimmune-suppressing Treg cells to treat and prevent RA.

Effect of tumor necrosis factor inhibition on spinal inflammation and spinal ankylosis in SKG mice

To prevent spinal progression in ankylosing spondylitis, initiating TNF-inhibitor treatment as early as possible is suggested. However, the outcomes are inconsistent in previous clinical studies. Here, we investigated the effect of TNF inhibition alone on spinal progression when used during arthritis development in a murine model. We injected 8-week-old SKG mice with curdlan (curdlan group). We injected adalimumab at 3 and 9 weeks after the first curdlan injection (ADA group). The clinical scores of peripheral arthritis decreased in the ADA group at 3 weeks after first adalimumab injection. Using positron emission tomography–magnetic resonance imaging and histologic examination, spinal inflammation was observed in the curdlan group, and was significantly deceased in the ADA group. However, spinal osteoblast activities by imaging using OsteoSense 680 EX and bone metabolism-related cytokines such as receptor activator of nuclear factor-kappa B ligand, osteoprotegerin, Dickkopf-1, and sclerostin levels except IL-17A level were not different between the two groups. We conclude that treating TNF inhibitor alone reduced peripheral arthritis score and spinal inflammation in curdlan-injected SKG mice but did not decrease the spinal osteoblast activity, suggesting little effect on spinal ankylosis.

Thymocyte selection: From signaling to epigenetic regulation

During thymocyte development at the double positive stage, thymocytes are subjected to a TCR quality check process termed "thymocyte selection." TCRs with proper binding capabilities to MHC molecules (with self-peptide) are able to transduce cell survival signals and allow the continuing of development to single positive T cells. It has been known that TCRs in DP cells can transduce signals with higher efficiency than peripheral mature T cells, even though they share most of the signaling components. Recent studies have revealed some thymocyte-specific signaling modulators including Themis and Tespa1. The activation of TCR signaling during positive selection results in the activation of several key transcription factors and extensive gene expression change, which has been revealed by newly developed systemic transcriptome analysis tools, and could be used for the evaluation of positive selection process. The fate determination postpositive selection is also governed on the epigenetic level including both DNA methylation and histone modifications.

Ablation of core fucosylation attenuates the signal transduction via T cell receptor to suppress the T cell development

Precise glycosylation plays a crucial and distinctive role in thymic T cell development. The core fucosylation is dramatically up-regulated at the transition from CD4^-CD8^- (DN) to CD4⁺CD8⁺ (DP) in the thymic development. Ablation of core fucosylation in T cells did reduce the size of the thymus due to a significant loss of CD4⁺ SP, CD8⁺ SP and DP thymocytes in core fucosyltransferase (Fut8) knockout (Fut8^-/-) mice. T cell receptors (TCRs) are heavily core fucosylated glycoproteins. Loss of core fucosylation of TCR contributed to the reduced phosphorylation of ZAP70 (pZAP70) in Fut8^-/- DP cells was observed. Compare to the Fut8^+/+OT-II DP thymocytes, pZAP70 was significantly reduced in Fut8^-/- OT-II DP thymocytes with OVA_323-339 stimulation. Also, the pZAP70 of Fut8^+/+OT-I DP thymocytes with OVA_257-264 stimulation was remarkably attenuated by treatment of the fucosidase. Upon anti-CD3/CD28 Abs stimulation, the increased apoptosis was found in Fut8^-/- thymocytes compared with Fut8^+/+ thymocytes. Moreover, the TCR^hiCD69^hi (post-positive selection thymocytes) was markedly depleted in the Fut8^-/- thymus without any stimulation. The expression of CD5 was significantly down-regulated on the DP cells in the Fut8^-/- thymus. Our results therefore demonstrate that ablation of core fucosylation results in the abnormal T cell development due to the attenuated signaling via TCR.

Coexpression of YY1 Is Required to Elaborate the Effector Functions Controlled by PLZF in NKT Cells

The promyelocytic leukemia zinc-finger transcription factor (PLZF) is essential for nearly all of the unique, innate-like functions and characteristics of NKT cells. It is not known, however, if the activity of PLZF is regulated by other factors. In this article, we show that the function of PLZF is completely dependent on the transcription factor Yin Yang 1 (YY1). Mouse NKT cells expressing wild-type levels of PLZF, but deficient for YY1, had developmental defects, lost their characteristic "preformed" mRNA for cytokines, and failed to produce cytokine protein upon primary activation. Immunoprecipitation experiments showed that YY1 and PLZF were coassociated. Taken together, these biochemical and genetic data show that the broadly expressed transcription factor, YY1, is required for the cell-specific "master regulator" functions of PLZF.

ZAP-70 Regulates Autoimmune Arthritis via Alterations in T Cell Activation and Apoptosis

T cells play an essential role in the pathogenesis of both human rheumatoid arthritis (RA) and its murine models. A key molecule in T cell activation is ZAP-70, therefore we aimed to investigate the effects of partial ZAP-70 deficiency on the pathogenesis of recombinant human G1(rhG1)-induced arthritis (GIA), a well-established mouse model of RA. Arthritis was induced in BALB/c and ZAP-70^+/- heterozygous mice. Disease progression was monitored using a scoring system and in vivo imaging, antigen-specific proliferation, cytokine and autoantibody production was measured and T cell apoptotic pathways were analyzed. ZAP-70^+/- mice developed a less severe arthritis, as shown by both clinical picture and in vitro parameters (decreased T cell proliferation, cytokine and autoantibody production). The amount of cleaved Caspase-3 increased in arthritic ZAP-70^+/- T cells, with no significant changes in cleaved Caspase-8 and -9 levels; although expression of Bim, Bcl-2 and Cytochrome C showed alterations. Tyrosine phosphorylation was less pronounced in arthritic ZAP-70^+/- T cells and the amount of Cbl-b-a negative regulator of T cell activation-decreased as well. We hypothesize that the less severe disease seen in the partial absence of ZAP-70 might be caused by the decreased T cell activation accompanied by increased apoptosis.

T Cell Receptor Expression Timing and Signal Strength in the Functional Differentiation of Invariant Natural Killer T Cells

The CD1d-restricted Vα14 invariant NKT (iNKT) cell lineage in mice (Vα24 in humans) represents an evolutionary conserved innate-like immune cell type that recognizes glycolipid antigens. Because of their unique ability to promptly secrete copious amounts of both pro-inflammatory and anti-inflammatory cytokines, typically produced by different T helper cell types, iNKT cells are implicated in the regulation of various pathologic conditions such as infection, allergy, autoimmune disease, maintenance of transplantation tolerance, and cancer. This striking multifaceted role in immune regulation is correlated with the presence of multiple functionally distinct iNKT cell subsets that can be distinguished based on the expression of characteristic surface markers and transcription factors. However, to date it, remains largely unresolved how this puzzling diversity of iNKT cell functional subsets emerges and what factors dictate the type of effector cell differentiation during the thymic differentiation considering the mono-specific nature of their T cell receptor (TCR) and their selecting molecule CD1d. Here, we summarize recent findings focusing on the role of TCR-mediated signaling and discuss possible mechanisms that may influence the sub-lineage choice of iNKT cells.

T cell receptor signaling for γδT cell development

T cells are central to the vertebrate immune system. Two distinct types of T cells, αβT and γδT cells, express different types of T cell antigen receptors (TCRs), αβTCR and γδTCR, respectively, that are composed of different sets of somatically rearranged TCR chains and CD3 subunits. γδT cells have recently attracted considerable attention due to their ability to produce abundant cytokines and versatile roles in host defense, tissue regeneration, inflammation, and autoimmune diseases. Both αβT and γδT cells develop in the thymus. Unlike the development of αβT cells, which depends on αβTCR-mediated positive and negative selection, the development of γδT cells, including the requirement of γδTCR, has been less well understood. αβT cells differentiate into effector cells in the peripheral tissues, whereas γδT cells acquire effector functions during their development in the thymus. In this review, we will discuss the current state of knowledge of the molecular mechanism of TCR signal transduction and its role in the thymic development of γδT cells, particularly highlighting a newly discovered mechanism that controls proinflammatory γδT cell development.

Prefoldin 5 and Anti-prefoldin 5 Antibodies as Biomarkers for Uveitis in Ankylosing Spondylitis

Objective: Uveitis is the most common extra-articular manifestation of ankylosing spondylitis (AS), for which no diagnostic biomarkers have been identified. This study was conducted to identify biomarker for uveitis in AS.

Methods: To identify autoantibodies associated with uveitis in AS, we performed human protein microarray analysis using sera derived from various autoimmune diseases and ELISA analysis of sera derived from AS and rheumatoid arthritis patients. In the curdlan-induced SKG mice model, ophthalmic examination was performed at week 8 post-immunization and histologic examination of the ocular lesions performed at week 16 post-immunization. Serum levels of target antibodies were assessed at various time-points. To evaluate the functional role of specific autoantibodies, an in vitro apoptosis assay using ARPE-19 cells was performed.

Results: Reactivity against prefoldin subunit 5 (PFDN5) was identified in AS with uveitis. Levels of anti-PFDN5 antibodies and PFDN5 in sera from AS with uveitis patients were significantly higher than those in AS without uveitis. At week 8, half of curdlan-treated SKG mice developed anterior uveitis, while all of them developed histologically confirmed uveitis at week 16. The levels of anti-PFDN5 antibodies increased over time in the sera of curdlan-treated SKG mice along with increased expression of PFDN5 and apoptosis in the ocular lesions. Knockdown of PFDN5 in ARPE19 cells resulted in increased apoptosis, suggesting a protective role of PFDN5 against cell death in uveitis.

Conclusion: AS patients with uveitis have increased levels of anti-PFDN5 antibodies, and our findings suggest that anti-PFDN5 antibodies could provide a biomarker for uveitis in AS.

ZAP70 deficiency promotes reverse cholesterol transport through MAPK/ERK pathway in Jurkat cell

BACKGROUND

Lots of studies have demonstrated that immune cells could regulate reverse cholesterol transport (RCT). However, neither T cell receptor (TCR) signalling nor Zeta-chain associated protein 70 (ZAP70) have been demonstrated to be associated with RCT. To investigate this association, we used a ZAP70-deficient Jurkat-derived mutant, P116 cell line, to detect the effect of ZAP70 on RCT and inflammatory response. ZAP70 deficiency improved cholesterol efflux capacity by 14%. Meanwhile, mRNA and proteins expression of RCT regulatory proteins such as ABCA1, ABCG1 and SR-BI were increased in P116 cells. ZAP70-deficiency had no influence on LXR-α and PPAR-γ. Regarding the inflammatory response, the mRNA expression and secretion of pro-atherosclerotic cytokines, TNF-α, IFN-γ, IL-2 and IL-6, were significantly decreased in the ZAP70-deficient cell line. Activation of MAP kinases cascades, as determined by of ERK, JNK and p38 MAPK phosphorylation, were found to be inhibited in the absence of ZAP70. Specific inhibition of ERK, JNK and p38 MAPK activity was also found to decreased TNF-α, IFN-γ, and IL-6 secretion. However, only the ERK inhibition was observed to reduce IL-2 secretion, improve cholesterol efflux capacity and increase expression of ABCA1, ABCG1 and SR-BI without increasing LXR-α and PPAR-γ. Using ChIP assay to detect the binding of LXR-α to LXRE, which promotes the expression of ABCG1, we found that inhibiting ERK improved binding without increasing LXR-α levels. Thus, we speculate that ZAP70-deficiency may improve RCT and decrease the inflammatory response of T cells. Furthermore, these effects are probably achieved via ERK signalling pathway.

Emerging insights into human health and NK cell biology from the study of NK cell deficiencies

Human NK cells are innate immune effectors that play a critical roles in the control of viral infection and malignancy. The importance of their homeostasis and function can be demonstrated by the study of patients with primary immunodeficiencies (PIDs), which are part of the family of diseases known as inborn defects of immunity. While NK cells are affected in many PIDs in ways that may contribute to a patient's clinical phenotype, a small number of PIDs have an NK cell abnormality as their major immunological defect. These PIDs can be collectively referred to as NK cell deficiency (NKD) disorders and include effects upon NK cell numbers, subsets, and/or functions. The clinical impact of NKD can be severe including fatal viral infection, with particular susceptibility to herpesviral infections, such as cytomegalovirus, varicella zoster virus, and Epstein-Barr virus. While NKD is rare, studies of these diseases are important for defining specific requirements for human NK cell development and homeostasis. New themes in NK cell biology are emerging through the study of both known and novel NKD, particularly those affecting cell cycle and DNA damage repair, as well as broader PIDs having substantive impact upon NK cells. In addition, the discovery of NKD that affects other innate lymphoid cell (ILC) subsets opens new doors for better understanding the relationship between conventional NK cells and other ILC subsets. Here, we describe the biology underlying human NKD, particularly in the context of new insights into innate immune cell function, including a discussion of recently described NKD with accompanying effects on ILC subsets. Given the impact of these disorders upon human immunity with a common focus upon NK cells, the unifying message of a critical role for NK cells in human host defense singularly emerges.

Rare Genetic Blood Disease Modeling in Zebrafish

Hematopoiesis results in the correct formation of all the different blood cell types. In mammals, it starts from specific hematopoietic stem and precursor cells residing in the bone marrow. Mature blood cells are responsible for supplying oxygen to every cell of the organism and for the protection against pathogens. Therefore, inherited or de novo genetic mutations affecting blood cell formation or the regulation of their activity are responsible for numerous diseases including anemia, immunodeficiency, autoimmunity, hyper- or hypo-inflammation, and cancer. By definition, an animal disease model is an analogous version of a specific clinical condition developed by researchers to gain information about its pathophysiology. Among all the model species used in comparative medicine, mice continue to be the most common and accepted model for biomedical research. However, because of the complexity of human diseases and the intrinsic differences between humans and other species, the use of several models (possibly in distinct species) can often be more helpful and informative than the use of a single model. In recent decades, the zebrafish (Danio rerio) has become increasingly popular among researchers, because it represents an inexpensive alternative compared to mammalian models, such as mice. Numerous advantages make it an excellent animal model to be used in genetic studies and in particular in modeling human blood diseases. Comparing zebrafish hematopoiesis to mammals, it is highly conserved with few, significant differences. In addition, the zebrafish model has a high-quality, complete genomic sequence available that shows a high level of evolutionary conservation with the human genome, empowering genetic and genomic approaches. Moreover, the external fertilization, the high fecundity and the transparency of their embryos facilitate rapid, in vivo analysis of phenotypes. In addition, the ability to manipulate its genome using the last genome editing technologies, provides powerful tools for developing new disease models and understanding the pathophysiology of human disorders. This review provides an overview of the different approaches and techniques that can be used to model genetic diseases in zebrafish, discussing how this animal model has contributed to the understanding of genetic diseases, with a specific focus on the blood disorders.