Intracellular complement and immunometabolism: The advantages of compartmentalization

The complement system is a proteolytic cascade triggered by pathogen and danger-associated molecular patterns, with resultant outcomes of inflammation, cellular activation, and opsonization of material for removal by phagocytosis. While first discovered as an activity in serum, it is now recognized that complement components play important roles at local and individual cell-intrinsic levels. In particular, apart from the extracellular serum activities of complement, it is now believed that complement also acts intracellularly, as part of a cellular signal transduction cascade that can stimulate cellular survival and activation, and individual immune cell phenotypes, via effects on cellular metabolism. This review will describe what is currently known about how complement functions in intracellular signal transduction, and outline the functional advantages of a compartmentalized and intracellular complement system.

Integrins in Health and Disease-Suitable Targets for Treatment?

Integrin receptors are heterodimeric surface receptors that play multiple roles regarding cell-cell communication, signaling, and migration. The four members of the β2 integrin subfamily are composed of an alternative α (CD11a-d) subunit, which determines the specific receptor properties, and a constant β (CD18) subunit. This review aims to present insight into the multiple immunological roles of integrin receptors, with a focus on β2 integrins that are specifically expressed by leukocytes. The pathophysiological role of β2 integrins is confirmed by the drastic phenotype of patients suffering from leukocyte adhesion deficiencies, most often resulting in severe recurrent infections and, at the same time, a predisposition for autoimmune diseases. So far, studies on the role of β2 integrins in vivo employed mice with a constitutive knockout of all β2 integrins or either family member, respectively, which complicated the differentiation between the direct and indirect effects of β2 integrin deficiency for distinct cell types. The recent generation and characterization of transgenic mice with a cell-type-specific knockdown of β2 integrins by our group has enabled the dissection of cell-specific roles of β2 integrins. Further, integrin receptors have been recognized as target receptors for the treatment of inflammatory diseases as well as tumor therapy. However, whereas both agonistic and antagonistic agents yielded beneficial effects in animal models, the success of clinical trials was limited in most cases and was associated with unwanted side effects. This unfavorable outcome is most probably related to the systemic effects of the used compounds on all leukocytes, thereby emphasizing the need to develop formulations that target distinct types of leukocytes to modulate β2 integrin activity for therapeutic applications.

Maladaptive T-Cell Metabolic Fitness in Autoimmune Diseases

Immune surveillance and adaptive immune responses, involving continuously circulating and tissue-resident T-lymphocytes, provide host defense against infectious agents and possible malignant transformation while avoiding autoimmune tissue damage. Activation, migration, and deployment of T-cells to affected tissue sites are crucial for mounting an adaptive immune response. An effective adaptive immune defense depends on the ability of T-cells to dynamically reprogram their metabolic requirements in response to environmental cues. Inability of the T-cells to adapt to specific metabolic demands may skew cells to become either hyporesponsive (creating immunocompromised conditions) or hyperactive (causing autoimmune tissue destruction). Here, we review maladaptive T-cell metabolic fitness that can cause autoimmune diseases and discuss how T-cell metabolic programs can potentially be modulated to achieve therapeutic benefits.

Synergy between Th1 and Th2 responses during endometriosis: A review of current understanding

Endometriosis is widely perceived as an estrogen-dependent chronic disorder with infertility and pelvic pain. Although the etiology of endometriosis has remained elusive, many studies have proclaimed the relevance of immune system disorders with endometriosis. With the discovery that the dysregulation of multiple biological functions in endometriosis is caused by the aberrant differentiation of T helper cells, a shift towards Th2 immune response may account for the disease progression. This review attempts to present mechanisms of cytokines, chemokines, signal pathways, transcription factors and some other factors related with the derivation of Th1/Th2 immune response involved in the development of endometriosis. The current understanding of treatment approaches and potential therapeutic targets will also be outlined with brief discussion.

The Role of LFA-1 for the Differentiation and Function of Regulatory T Cells—Lessons Learned from Different Transgenic Mouse Models

Regulatory T cells (Treg) are essential for the maintenance of peripheral tolerance. Treg dysfunction results in diverse inflammatory and autoimmune diseases with life-threatening consequences. β2-integrins (CD11a-d/CD18) play important roles in the migration of leukocytes into inflamed tissues and cell signaling. Of all β2-integrins, T cells, including Treg, only express CD11a/CD18, termed lymphocyte function-associated antigen 1 (LFA-1), on their surface. In humans, loss-of-function mutations in the common subunit CD18 result in leukocyte adhesion deficiency type-1 (LAD-1). Clinical symptoms vary depending on the extent of residual β2-integrin function, and patients may experience leukocytosis and recurrent infections. Some patients can develop autoimmune diseases, but the immune processes underlying the paradoxical situation of immune deficiency and autoimmunity have been scarcely investigated. To understand this complex phenotype, different transgenic mouse strains with a constitutive knockout of β2-integrins have been established. However, since a constitutive knockout affects all leukocytes and may limit the validity of studies focusing on their cell type-specific role, we established a Treg-specific CD18-floxed mouse strain. This mini-review aims to delineate the role of LFA-1 for the induction, maintenance, and regulatory function of Treg in vitro and in vivo as deduced from observations using the various β2-integrin-deficient mouse models.

Exhausted T cells hijacking the cancer-immunity cycle: Assets and liabilities

T cell exhaustion is an alternative differentiation path of T cells, sometimes described as a dysfunction. During the last decade, insights of T cell exhaustion acting as a bottle neck in the field of cancer immunotherapy have undoubtedly provoked attention. One of the main drivers of T cell exhaustion is prolonged antigen presentation, a prerequisite in the cancer-immunity cycle. The umbrella term "T cell exhaustion" comprises various stages of T cell functionalities, describing the dynamic, one-way exhaustion process. Together these qualities of T cells at the exhaustion continuum can enable tumor clearance, but if the exhaustion acquired timeframe is exceeded, tumor cells have increased possibilities of escaping immune system surveillance. This could be considered a tipping point where exhausted T cells switch from an asset to a liability. In this review, the contrary role of exhausted T cells is discussed.

Cell adhesion molecules and immunotherapy in advanced non-small cell lung cancer: Current process and potential application

Advanced non-small cell lung cancer (NSCLC) is a severe disease and still has high mortality rate after conventional treatment (e.g., surgical resection, chemotherapy, radiotherapy and targeted therapy). In NSCLC patients, cancer cells can induce immunosuppression, growth and metastasis by modulating cell adhesion molecules of both cancer cells and immune cells. Therefore, immunotherapy is increasingly concerned due to its promising anti-tumor effect and broader indication, which targets cell adhesion molecules to reverse the process. Among these therapies, immune checkpoint inhibitors (mainly anti-PD-(L)1 and anti-CTLA-4) are most successful and have been adapted as first or second line therapy in advanced NSCLC. However, drug resistance and immune-related adverse reactions restrict its further application. Further understanding of mechanism, adequate biomarkers and novel therapies are necessary to improve therapeutic effect and alleviate adverse effect.

An αvβ3 integrin checkpoint is critical for efficient TH2 cell cytokine polarization and potentiation of antigen-specific immunity

Naive CD4⁺ T lymphocytes initially undergo antigen-specific activation to promote a broad-spectrum response before adopting bespoke cytokine expression profiles shaped by intercellular microenvironmental cues, resulting in pathogen-focused modular cytokine responses. Interleukin (IL)-4-induced Gata3 upregulation is important for the helper type 2 T cell (T_H2 cell) polarization associated with anti-helminth immunity and misdirected allergic inflammation. Whether additional microenvironmental factors participate is unclear. Using whole mouse-genome CRISPR-Cas9 screens, we discovered a previously unappreciated role for αvβ3 integrin in T_H2 cell differentiation. Low-level αvβ3 expression by naive CD4⁺ T cells contributed to pan-T cell activation by promoting T-T cell clustering and IL-2/CD25/STAT5 signaling. Subsequently, IL-4/Gata3-induced selective upregulation of αvβ3 licensed intercellular αvβ3-Thy1 interactions among T_H2 cells, enhanced mammalian target of rapamycin (mTOR) signaling, supported differentiation and promoted IL-5/IL-13 production. In mice, αvβ3 was required for efficient, allergen-driven, antigen-specific lung T_H2 cell responses. Thus, αvβ3-expressing T_H2 cells form multicellular factories to propagate and amplify T_H2 cell responses.

Arc Regulates Transcription of Genes for Plasticity, Excitability and Alzheimer’s Disease

The immediate early gene Arc is a master regulator of synaptic function and a critical determinant of memory consolidation. Here, we show that Arc interacts with dynamic chromatin and closely associates with histone markers for active enhancers and transcription in cultured rat hippocampal neurons. Both these histone modifications, H3K27Ac and H3K9Ac, have recently been shown to be upregulated in late-onset Alzheimer’s disease (AD). When Arc induction by pharmacological network activation was prevented using a short hairpin RNA, the expression profile was altered for over 1900 genes, which included genes associated with synaptic function, neuronal plasticity, intrinsic excitability, and signalling pathways. Interestingly, about 100 Arc-dependent genes are associated with the pathophysiology of AD. When endogenous Arc expression was induced in HEK293T cells, the transcription of many neuronal genes was increased, suggesting that Arc can control expression in the absence of activated signalling pathways. Taken together, these data establish Arc as a master regulator of neuronal activity-dependent gene expression and suggest that it plays a significant role in the pathophysiology of AD.

IFNγ-primed periodontal ligament cells regulate T-cell responses via IFNγ-inducible mediators and ICAM-1-mediated direct cell contact

Periodontal ligament (PDL) cells help maintain tissue homeostasis by balancing PDL tissue inflammation and regeneration. However, the mechanisms by which interferon γ (IFNγ) modulate this process are not yet fully understood. The present study aimed to examine the effect of primed and non-primed PDL cells with IFNγ on the viability and differentiation of T lymphocytes and its functional consequences. The results showed that IFNγ-primed PDL cells possessed enhanced immunosuppression by suppressing T-lymphocyte viability and directing T-lymphocyte differentiation towards a higher T helper (Th) Th2/Th1 ratio. Suppression of T-cell viability was mainly mediated by IFNγ-inducible secreted mediators, which was prevented in the presence of direct cell contact, probably by intercellular adhesion molecule-1 (ICAM-1)-induced PI3 K-mediated transforming growth factor β1 expression in PDL cells. By contrast, ICAM-1 activation augmented IFNγ-induced IFNγ and interleukin-6 expression in PDL cells, which in turn modulated T-cell differentiation. The resulting interaction between these two cell types activated macrophage and suppressed osteoclast differentiation. In conclusion, the results have shown, for the first time to our knowledge, that primed and non-primed PDL cells with IFNγ differentially control T-cell responses via IFNγ-inducible mediators and ICAM-1-mediated direct cell contact, suggesting the role of PDL cells in shifting an inflammatory phase towards a regenerative phase.

The Recombinant Eg.P29-Mediated miR-126a-5p Promotes the Differentiation of Mouse Naive CD4+ T Cells via DLK1-Mediated Notch1 Signal Pathway

Cystic echinococcosis (CE) is a zoonotic parasitic disease spread worldwide caused by Echinococcus granulosus (Eg), which sometimes causes serious damage; however, in many cases, people are not aware that they are infected. A number of recombinant vaccines based on Eg are used to evaluate their effectiveness against the infection. Our previous report showed that recombinant Eg.P29 (rEg.P29) has a marvelous immunoprotection and can induce Th1 immune response. Furthermore, data of miRNA microarray in mice spleen CD4⁺ T cells showed that miR-126a-5p was significantly elevated 1 week after immunization by using rEg.P29. Therefore, in this perspective, we discussed the role of miR-126a-5p in the differentiation of naive CD4⁺ T cells into Th1/Th2 under rEg.P29 immunization and determined the mechanisms associated with delta-like 1 homolog (DLK1) and Notch1 signaling pathway. One week after P29 immunization of mice, we found that miR-126a-5p was significantly increased and DLK1 expression was decreased, while Notch1 pathway activation was enhanced and Th1 response was significantly stronger. The identical conclusion was obtained by overexpression of mmu-miR-126a-5p in primary naive CD4⁺ T cells in mice. Intriguingly, mmu-miR-126a-5p was significantly raised in serum from mice infected with protoscolex in the early stages of infection and markedly declined in the late stages of infection, while has-miR-126-5p expression was dramatically reduced in serum from CE patients. Taken together, we show that miR-126a-5p functions as a positive regulator of Notch1-mediated differentiation of CD4⁺ T cells into Th1 through downregulating DLK1 in vivo and in vitro. Hsa-miR-126-5p is potentially a very promising diagnostic biomarker for CE.

New Approaches to Dendritic Cell-Based Therapeutic Vaccines Against HIV-1 Infection

Due to the success of combined antiretroviral therapy (cART) in recent years, the pathological outcome of Human Immunodeficiency Virus type 1 (HIV-1) infection has improved substantially, achieving undetectable viral loads in most cases. Nevertheless, the presence of a viral reservoir formed by latently infected cells results in patients having to maintain treatment for life. In the absence of effective eradication strategies against HIV-1, research efforts are focused on obtaining a cure. One of these approaches is the creation of therapeutic vaccines. In this sense, the most promising one up to now is based on the establishing of the immunological synapse between dendritic cells (DCs) and T lymphocytes (TL). DCs are one of the first cells of the immune system to encounter HIV-1 by acting as antigen presenting cells, bringing about the interaction between innate and adaptive immune responses mediated by TL. Furthermore, TL are the end effector, and their response capacity is essential in the adaptive elimination of cells infected by pathogens. In this review, we summarize the knowledge of the interaction between DCs with TL, as well as the characterization of the specific T-cell response against HIV-1 infection. The use of nanotechnology in the design and improvement of vaccines based on DCs has been researched and presented here with a special emphasis.

GSK3β Interacts With CRMP2 and Notch1 and Controls T-Cell Motility

The trafficking of T-cells through peripheral tissues and into afferent lymphatic vessels is essential for immune surveillance and an adaptive immune response. Glycogen synthase kinase 3β (GSK3β) is a serine/threonine kinase and regulates numerous cell/tissue-specific functions, including cell survival, metabolism, and differentiation. Here, we report a crucial involvement of GSK3β in T-cell motility. Inhibition of GSK3β by CHIR-99021 or siRNA-mediated knockdown augmented the migratory behavior of human T-lymphocytes stimulated via an engagement of the T-cell integrin LFA-1 with its ligand ICAM-1. Proteomics and protein network analysis revealed ongoing interactions among GSK3β, the surface receptor Notch1 and the cytoskeletal regulator CRMP2. LFA-1 stimulation in T-cells reduced Notch1-dependent GSK3β activity by inducing phosphorylation at Ser9 and its nuclear translocation accompanied by the cleaved Notch1 intracellular domain and decreased GSK3β-CRMP2 association. LFA-1-induced or pharmacologic inhibition of GSK3β in T-cells diminished CRMP2 phosphorylation at Thr514. Although substantial amounts of CRMP2 were localized to the microtubule-organizing center in resting T-cells, this colocalization of CRMP2 was lost following LFA-1 stimulation. Moreover, the migratory advantage conferred by GSK3β inhibition in T-cells by CHIR-99021 was lost when CRMP2 expression was knocked-down by siRNA-induced gene silencing. We therefore conclude that GSK3β controls T-cell motility through interactions with CRMP2 and Notch1, which has important implications in adaptive immunity, T-cell mediated diseases and LFA-1-targeted therapies.

The steroidal lactone withaferin A impedes T-cell motility by inhibiting the kinase ZAP70 and subsequent kinome signaling

The steroidal lactone withaferin A (WFA) is a dietary phytochemical, derived from Withania somnifera. It exhibits a wide range of biological properties, including immunomodulatory, anti-inflammatory, antistress, and anticancer activities. Here we investigated the effect of WFA on T-cell motility, which is crucial for adaptive immune responses as well as autoimmune reactions. We found that WFA dose-dependently (within the concentration range of 0.3–1.25 μM) inhibited the ability of human T-cells to migrate via cross-linking of the lymphocyte function-associated antigen-1 (LFA-1) integrin with its ligand, intercellular adhesion molecule 1 (ICAM-1). Coimmunoprecipitation of WFA interacting proteins and subsequent tandem mass spectrometry identified a WFA-interactome consisting of 273 proteins in motile T-cells. In particular, our data revealed significant enrichment of the zeta-chain-associated protein kinase 70 (ZAP70) and cytoskeletal actin protein interaction networks upon stimulation. Phospho-peptide mapping and kinome analysis substantiated kinase signaling downstream of ZAP70 as a key WFA target, which was further confirmed by bait-pulldown and Western immunoblotting assays. The WFA-ZAP70 interaction was disrupted by a disulfide reducing agent dithiothreitol, suggesting an involvement of cysteine covalent binding interface. In silico docking predicted WFA binding to ZAP70 at cystine 560 and 564 residues. These findings provide a mechanistic insight whereby WFA binds to and inhibits the ZAP70 kinase and impedes T-cell motility. We therefore conclude that WFA may be exploited to pharmacologically control host immune responses and potentially prevent autoimmune-mediated pathologies.

LFA-1 in T cell priming, differentiation, and effector functions

The integrin LFA-1 is crucial for T cell entry into mammalian lymph nodes and tissues, and for promoting interactions with antigen-presenting cells (APCs). However, it is increasingly evident that LFA-1 has additional key roles beyond the mere support of adhesion between T cells, the endothelium, and/or APCs. These include roles in homotypic T cell-T cell (T-T) communication, the induction of intracellular complement activity underlying Th1 effector cell polarization, and the support of long-lasting T cell memory. Here, we briefly summarize current knowledge of LFA-1 biology, discuss novel cytoskeletal regulators of LFA-1 functions, and review new aspects of LFA-1 mechanobiology that are relevant to its function in immunological synapses and in specific pathologies arising from LFA-1 dysregulation.

The Multiple Roles of the Cytosolic Adapter Proteins ADAP, SKAP1 and SKAP2 for TCR/CD3 -Mediated Signaling Events

T cells are the key players of the adaptive immune response. They coordinate the activation of other immune cells and kill malignant and virus-infected cells. For full activation T cells require at least two signals. Signal 1 is induced after recognition of MHC/peptide complexes presented on antigen presenting cells (APCs) by the clonotypic TCR (T-cell receptor)/CD3 complex whereas Signal 2 is mediated via the co-stimulatory receptor CD28, which binds to CD80/CD86 molecules that are present on APCs. These signaling events control the activation, proliferation and differentiation of T cells. In addition, triggering of the TCR/CD3 complex induces the activation of the integrin LFA-1 (leukocyte function associated antigen 1) leading to increased ligand binding (affinity regulation) and LFA-1 clustering (avidity regulation). This process is termed "inside-out signaling". Subsequently, ligand bound LFA-1 transmits a signal into the T cells ("outside-in signaling") which enhances T-cell interaction with APCs (adhesion), T-cell activation and T-cell proliferation. After triggering of signal transducing receptors, adapter proteins organize the proper processing of membrane proximal and intracellular signals as well as the activation of downstream effector molecules. Adapter proteins are molecules that lack enzymatic or transcriptional activity and are composed of protein-protein and protein-lipid interacting domains/motifs. They organize and assemble macromolecular complexes (signalosomes) in space and time. Here, we review recent findings regarding three cytosolic adapter proteins, ADAP (Adhesion and Degranulation-promoting Adapter Protein), SKAP1 and SKAP2 (Src Kinase Associated Protein 1 and 2) with respect to their role in TCR/CD3-mediated activation, proliferation and integrin regulation.

T-Cell Adhesion in Healthy and Inflamed Skin

The diverse populations of tissue-resident and transitory T cells present in the skin share a common functional need to enter, traverse, and interact with their environment. These processes are largely dependent on the regulated expression of adhesion molecules, such as selectins and integrins, which mediate bidirectional interactions between immune cells and skin stroma. Dysregulation and engagement of adhesion pathways contribute to ectopic T-cell activity in tissues, leading to the initiation and/or exacerbation of chronic inflammation. In this paper, we review how the molecular interactions supported by adhesion pathways contribute to T-cell dynamics and function in the skin. A comprehensive understanding of the molecular mechanisms underpinning T-cell adhesion in inflammatory skin disorders will facilitate the development of novel tissue-specific therapeutic strategies.

Optimization of T Cell Redirecting Strategies: Obtaining Inspirations From Natural Process of T Cell Activation

Chimeric antigen receptors (CARs) or bispecific antibodies (bsAbs) redirected T cell against tumors is one of the most promising immunotherapy approaches. However, insufficient clinical outcomes are still observed in treatments of both solid and non-solid tumors. Limited efficacy and poor persistence are two major challenges in redirected T cell therapies. The immunological synapse (IS) is a vital component during the T cell response, which largely determines the clinical outcomes of T cell-based therapies. Here, we review the structural and signaling characteristics of IS formed by natural T cells and redirected T cells. Furthermore, inspired by the elaborate natural T cell receptor-mediated IS, we provide potential strategies for higher efficacy and longer persistence of redirected T cells.

Complement Has Brains-Do Intracellular Complement and Immunometabolism Cooperate in Tissue Homeostasis and Behavior?

The classical liver-derived and serum-effective complement system is well appreciated as a key mediator of host protection via instruction of innate and adaptive immunity. However, recent studies have discovered an intracellularly active complement system, the complosome, which has emerged as a central regulator of the core metabolic pathways fueling human immune cell activity. Induction of expression of components of the complosome, particularly complement component C3, during transmigration from the circulation into peripheral tissues is a defining characteristic of monocytes and T cells in tissues. Intracellular complement activity is required to induce metabolic reprogramming of immune cells, including increased glycolytic flux and OXPHOS, which drive the production of the pro-inflammatory cytokine IFN-γ. Consequently, reduced complosome activity translates into defects in normal monocyte activation, faulty Th1 and cytotoxic T lymphocyte responses and loss of protective tissue immunity. Intriguingly, neurological research has identified an unexpected connection between the physiological presence of innate and adaptive immune cells and certain cytokines, including IFN-γ, in and around the brain and normal brain function. In this opinion piece, we will first review the current state of research regarding complement driven metabolic reprogramming in the context of immune cell tissue entry and residency. We will then discuss how published work on the role of IFN-γ and T cells in the brain support a hypothesis that an evolutionarily conserved cooperation between the complosome, cell metabolism and IFN-γ regulates organismal behavior, as well as immunity.

Notch 1 Is Involved in CD4+ T Cell Differentiation Into Th1 Subtype During Helicobacter pylori Infection

Helicobacter pylori infection induces CD4⁺ T differentiation cells into IFN-γ-producing Th1 cells. However, the details of mechanism underlying this process remain unclear. Notch signal pathway has been reported to regulate the differentiation of CD4⁺ T cells into Th1 subtype in many Th1-mediated inflammatory disorders but not yet in H. pylori infection. In the present study, the mRNA expression pattern of CD4⁺ T cells in H. pylori-infected patients differed from that of healthy control using Human Signal Transduction Pathway Finder RT2 Profiler PCR Array, and this alteration was associated with Notch signal pathway, as analyzed by Bioinformation. Quantitative real-time PCR showed that the mRNA expression of Notch1 and its target gene Hes-1 in CD4⁺ T cells of H. pylori-infected individuals increased compared with the healthy controls. In addition, the mRNA expression of Th1 master transcription factor T-bet and Th1 signature cytokine IFN-γ was both upregulated in H. pylori-infected individuals and positively correlated with Notch1 expression. The increased protein level of Notch1 and IFN-γ were also observed in H. pylori-infected individuals confirmed by flow cytometry and ELISA. In vitro, inhibition of Notch signaling decreased the mRNA expression of Notch1, Hes-1, T-bet, and IFN-γ, and reduced the protein levels of Notch1 and IFN-γ and the secretion of IFN-γ in CD4⁺ T cells stimulated by H. pylori. Collectively, this is the first evidence that Notch1 is upregulated and involved in the differentiation of Th1 cells during H. pylori infection, which will facilitate exploiting Notch1 as a therapeutic target for the control of H. pylori infection.

Diapedesis-Induced Integrin Signaling via LFA-1 Facilitates Tissue Immunity by Inducing Intrinsic Complement C3 Expression in Immune Cells

Intrinsic complement C3 activity is integral to human T helper type 1 (Th1) and cytotoxic T cell responses. Increased or decreased intracellular C3 results in autoimmunity and infections, respectively. The mechanisms regulating intracellular C3 expression remain undefined. We identified complement, including C3, as among the most significantly enriched biological pathway in tissue-occupying cells. We generated C3-reporter mice and confirmed that C3 expression was a defining feature of tissue-immune cells, including T cells and monocytes, occurred during transendothelial diapedesis, and depended on integrin lymphocyte-function-associated antigen 1 (LFA-1) signals. Immune cells from patients with leukocyte adhesion deficiency type 1 (LAD-1) had reduced C3 transcripts and diminished effector activities, which could be rescued proportionally by intracellular C3 provision. Conversely, increased C3 expression by T cells from arthritis patients correlated with disease severity. Our study defines integrins as key controllers of intracellular complement, demonstrates that perturbations in the LFA-1-C3-axis contribute to primary immunodeficiency, and identifies intracellular C3 as biomarker of severity in autoimmunity.

Integrins meet complement: The evolutionary tip of an iceberg orchestrating metabolism and immunity

Immunologists have recently realized that there is more to the classic innate immune sensor systems than just mere protection against invading pathogens. It is becoming increasingly clear that such sensors, including the inflammasomes, toll-like receptors, and the complement system, are heavily involved in the regulation of basic cell physiological processes and particularly those of metabolic nature. In fact, their "non-canonical" activities make sense as no system directing immune cell activity can perform such task without the need for energy. Further, many of these ancient immune sensors appeared early and concurrently during evolution, particularly during the developmental leap from the single-cell organisms to multicellularity, and therefore crosstalk heavily with each other. Here, we will review the current knowledge about the emerging cooperation between the major inter-cell communicators, integrins, and the cell-autonomous intracellularly and autocrine-active complement, the complosome, during the regulation of single-cell metabolism. LINKED ARTICLES: This article is part of a themed issue on Canonical and non-canonical functions of the complement system in health and disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.14/issuetoc.

Modes of Communication between T Cells and Relevance for Immune Responses

T cells are essential mediators of the adaptive immune system, which constantly patrol the body in search for invading pathogens. During an infection, T cells that recognise the pathogen are recruited, expand and differentiate into subtypes tailored to the infection. In addition, they differentiate into subsets required for short and long-term control of the pathogen, i.e., effector or memory. T cells have a remarkable degree of plasticity and heterogeneity in their response, however, their overall response to a given infection is consistent and robust. Much research has focused on how individual T cells are activated and programmed. However, in order to achieve a critical level of population-wide reproducibility and robustness, neighbouring cells and surrounding tissues have to provide or amplify relevant signals to tune the overall response accordingly. The characteristics of the immune response-stochastic on the individual cell level, robust on the global level-necessitate coordinated responses on a system-wide level, which facilitates the control of pathogens, while maintaining self-tolerance. This global coordination can only be achieved by constant cellular communication between responding cells, and faults in this intercellular crosstalk can potentially lead to immunopathology or autoimmunity. In this review, we will discuss how T cells mount a global, collective response, by describing the modes of T cell-T cell (T-T) communication they use and highlighting their physiological relevance in programming and controlling the T cell response.

T cell interactions with B cells during germinal center formation, a three-step model

Establishment of effective immunity against invading microbes depends on continuous generation of antibodies that facilitate pathogen clearance. Long-lived plasma cells with the capacity to produce high affinity antibodies evolve in germinal centers (GCs), where B cells undergo somatic hypermutation and are subjected to affinity-based selection. Here, we focus on the cellular interactions that take place early in the antibody immune response during GC colonization. Clones bearing B-cell receptors with different affinities and specificities compete for entry to the GC, at the boundary between the B-cell and T-cell zones in lymphoid organs. During this process, B cells compete for interactions with T follicular helper cells, which provide selection signals required for differentiation into GC cells and antibody secreting cells. These cellular engagements are long-lasting and depend on activation of adhesion molecules that support persistent interactions and promote transmission of signals between the cells. Here, we discuss how interactions between cognate T and B cells are primarily maintained by three types of molecular interactions: homophilic signaling lymphocytic activation molecule (SLAM) interactions, T-cell receptor: peptide-loaded major histocompatibility class II (pMHCII), and LFA-1:ICAMs. These essential components support a three-step process that controls clonal selection for entry into the antibody affinity maturation response in the GC, and establishment of long-lasting antibody-mediated immunity.

Role of Co-stimulatory Molecules in T Helper Cell Differentiation

CD4⁺ T cells play a central role in orchestrating the immune response to a variety of pathogens but also regulate autoimmune responses, asthma, allergic responses, as well as tumor immunity. To cover this broad spectrum of responses, naïve CD4⁺ T cells differentiate into one of several lineages of T helper cells, including Th1, Th2, Th17, and T_FH, as defined by their cytokine pattern and function. The fate decision of T helper cell differentiation integrates signals delivered through the T cell receptor, cytokine receptors, and the pattern of co-stimulatory signals received. In this review, we summarize the contribution of co-stimulatory and co-inhibitory receptors to the differentiation and maintenance of T helper cell responses.

Keratinocytes costimulate naive human T cells via CD2: a potential target to prevent the development of proinflammatory Th1 cells in the skin

The interplay between keratinocytes and immune cells, especially T cells, plays an important role in the pathogenesis of chronic inflammatory skin diseases. During psoriasis, keratinocytes attract T cells by releasing chemokines, while skin-infiltrating self-reactive T cells secrete proinflammatory cytokines, e.g., IFNγ and IL-17A, that cause epidermal hyperplasia. Similarly, in chronic graft-versus-host disease, allogenic IFNγ-producing Th1/Tc1 and IL-17-producing Th17/Tc17 cells are recruited by keratinocyte-derived chemokines and accumulate in the skin. However, whether keratinocytes act as nonprofessional antigen-presenting cells to directly activate naive human T cells in the epidermis remains unknown. Here, we demonstrate that under proinflammatory conditions, primary human keratinocytes indeed activate naive human T cells. This activation required cell contact and costimulatory signaling via CD58/CD2 and CD54/LFA-1. Naive T cells costimulated by keratinocytes selectively differentiated into Th1 and Th17 cells. In particular, keratinocyte-initiated Th1 differentiation was dependent on costimulation through CD58/CD2. The latter molecule initiated STAT1 signaling and IFNγ production in T cells. Costimulation of T cells by keratinocytes resulting in Th1 and Th17 differentiation represents a new explanation for the local enrichment of Th1 and Th17 cells in the skin of patients with a chronic inflammatory skin disease. Consequently, local interference with T cell–keratinocyte interactions may represent a novel strategy for the treatment of Th1 and Th17 cell-driven skin diseases.

Meningitic Escherichia coli-induced upregulation of PDGF-B and ICAM-1 aggravates blood-brain barrier disruption and neuroinflammatory response

Background

Blood-brain barrier (BBB) disruption and neuroinflammation are considered key mechanisms of pathogenic Escherichia coli invasion of the brain. However, the specific molecules involved in meningitic E. coli-induced BBB breakdown and neuroinflammatory response remain unclear. Our previous RNA-sequencing data from human brain microvascular endothelial cells (hBMECs) revealed two important host factors: platelet-derived growth factor-B (PDGF-B) and intercellular adhesion molecule-1 (ICAM-1), which were significantly upregulated in hBMECs after meningitic E. coli infection. Whether and how PDGF-B and ICAM-1 contribute to the development of E. coli meningitis are still unclear.

Methods

The western blot, real-time PCR, enzyme-linked immunosorbent assay, immunohistochemistry, and immunofluorescence were applied to verify the significant induction of PDGF-B and ICAM-1 by meningitic E. coli in vivo and in vitro. Evan’s blue assay and electric cell-substrate impedance sensing assay were combined to identify the effects of PDGF-B on BBB permeability. The CRISPR/Cas9 technology, cell-cell adhesion assay, and electrochemiluminescence assay were used to investigate the role of ICAM-1 in neuroinflammation subversion.

Results

We verified the significant induction of PDGF-B and ICAM-1 by meningitic E. coli in mouse as well as monolayer hBMECs models. Functionally, we showed that the increase of PDGF-B may directly enhance the BBB permeability by decreasing the expression of tight junction proteins, and the upregulation of ICAM-1 contributed to neutrophils or monocytes recruitment as well as neuroinflammation subversion in response to meningitic E. coli infection.

Conclusions

Our findings demonstrated the roles of PDGF-B and ICAM-1 in mediating bacterial-induced BBB damage as well as neuroinflammation, providing new concepts and potential targets for future prevention and treatment of bacterial meningitis.

Beta2-Integrins and Interacting Proteins in Leukocyte Trafficking, Immune Suppression, and Immunodeficiency Disease

Beta2-integrins are complex leukocyte-specific adhesion molecules that are essential for leukocyte (e.g., neutrophil, lymphocyte) trafficking, as well as for other immunological processes such as neutrophil phagocytosis and ROS production, and T cell activation. Intriguingly, however, they have also been found to negatively regulate cytokine responses, maturation, and migratory responses in myeloid cells such as macrophages and dendritic cells, revealing new, and unexpected roles of these molecules in immunity. Because of their essential role in leukocyte function, a lack of expression or function of beta2-integrins causes rare immunodeficiency syndromes, Leukocyte adhesion deficiency type I, and type III (LAD-I and LAD-III). LAD-I is caused by reduced or lost expression of beta2-integrins, whilst in LAD-III, beta2-integrins are expressed but dysfunctional because a major integrin cytoplasmic regulator, kindlin-3, is mutated. Interestingly, some LAD-related phenotypes such as periodontitis have recently been shown to be due to an uncontrolled inflammatory response rather than to an uncontrolled infection, as was previously thought. This review will focus on the recent advances concerning the regulation and functions of beta2-integrins in leukocyte trafficking, immune suppression, and immune deficiency disease.

Computational Analysis of Protein-Protein Interactions in Motile T-Cells

Analysis of protein-protein interactions is important for better understanding of molecular mechanisms involved in immune regulation and has potential for elaborating avenues for drug discovery targeting T-cell motility. Currently, only a small fraction of protein-protein interactions have been characterized in T-lymphocytes although there are several detection methods available. In this regard, computational approaches garner importance, with the continued explosion of genomic and proteomic data, for handling protein modeling and protein-protein interactions in large scale. Here, we describe a computational method to identify protein-protein interactions based on in silico protein design.

Isolation of Human Peripheral Blood T-Lymphocytes

Peripheral blood is the most common source of T-lymphocytes for in vitro culture. Here, we present a simple and standardized method for small- or large-scale isolation of viable T-lymphocytes and other mononuclear cells from fresh peripheral blood or buffy coat blood samples using the density gradient centrifugation. T-cells obtained using the protocol described here can be used for a variety of downstream analysis, including cellular, molecular, and functional assays.

Profiling Activity of Cellular Kinases in Migrating T-Cells

T-Lymphocyte kinases are important checkpoints that control T-cell motility by regulating a diverse range of signal transduction pathways. The distinct configuration of kinase events in T-cell could be used to fingerprint the status of T-cells. However, only small fraction human kinases have been characterized so far and little is known about the dynamics of the kinome in motile T-cells. Although several direct and indirect strategies exist to characterize cellular kinase activities, such as RNA interference, antibody arrays, enzyme kinetics, and mass spectrometry, this chapter focuses on an alternative multiplex phosphopeptide array-based methodology, which allows the kinome-wide identification of hyper-activated kinases involved in the regulation of T-cell migration.

The PI3K/Akt/GSK-3β/ROS/eIF2B pathway promotes breast cancer growth and metastasis via suppression of NK cell cytotoxicity and tumor cell susceptibility

Objective

To examine the effect of pSer9-GSK-3β on breast cancer and to determine whether the underlying metabolic and immunological mechanism is associated with ROS/eIF2B and natural killer (NK) cells.

Methods

We employed TWS119 to inactivate GSK-3β by phosphorylating Ser9 and explored its effect on breast cancer and NK cells. The expression of GSK-3β, natural killer group 2 member D (NKG2D) ligands, eIF2B was quantified by PCR and Western blot. We measured intracellular reactive oxygen species (ROS) and mitochondrial ROS using DCFH-DA and MitoSOX^TM probe, respectively, and conducted quantitative analysis of cellular respiration on 4T1 cells with mitochondrial respiratory chain complex I/III kits.

Results

Our investigation revealed that TWS119 downregulated NKG2D ligands (H60a and Rae1), suppressed the cytotoxicity of NK cells, and promoted the migration of 4T1 murine breast cancer cells. Nevertheless, LY290042, which attenuates p-GSK-3β formation by inhibiting the PI3K/Akt pathway, reversed these effects. We also found that higher expression of pSer9-GSK-3β induced higher levels of ROS, and observed that abnormality of mitochondrial respiratory chain complex I/III function induced the dysfunction of GSK-3β-induced electron transport chain, naturally disturbing the ROS level. In addition, the expression of NOX3 and NOX4 was significantly up-regulated, which affected the generation of ROS and associated with the metastasis of breast cancer. Furthermore, we found that the expression of pSer535-eIF2B promoted the expression of NKG2D ligands (Mult-1 and Rae1) following by expression of pSer9-GSK-3β and generation of ROS.

Conclusions

The PI3K/Akt/GSK-3β/ROS/eIF2B pathway could regulate NK cell activity and sensitivity of tumor cells to NK cells, which resulted in breast cancer growth and lung metastasis. Thus, GSK-3β is a promising target of anti-tumor therapy.

Crk adaptor proteins mediate actin-dependent T cell migration and mechanosensing induced by the integrin LFA-1

T cell entry into inflamed tissue involves firm adhesion, spreading, and migration of the T cells across endothelial barriers. These events depend on "outside-in" signals through which engaged integrins direct cytoskeletal reorganization. We investigated the molecular events that mediate this process and found that T cells from mice lacking expression of the adaptor protein Crk exhibited defects in phenotypes induced by the integrin lymphocyte function-associated antigen 1 (LFA-1), namely, actin polymerization, leading edge formation, and two-dimensional cell migration. Crk protein was an essential mediator of LFA-1 signaling-induced phosphorylation of the E3 ubiquitin ligase c-Cbl and its subsequent interaction with the phosphatidylinositol 3-kinase (PI3K) subunit p85, thus promoting PI3K activity and cytoskeletal remodeling. In addition, we found that Crk proteins were required for T cells to respond to changes in substrate stiffness, as measured by alterations in cell spreading and differential phosphorylation of the force-sensitive protein CasL. These findings identify Crk proteins as key intermediates coupling LFA-1 signals to actin remodeling and provide mechanistic insights into how T cells sense and respond to substrate stiffness.

The Role of Co-Stimulatory Molecules in Chagas Disease

Chagas disease, caused by Trypanosoma cruzi, is a potentially life-threatening tropical disease endemic to Latin American countries that affects approximately 8 million people. In the chronic phase of the disease, individuals are classified as belonging to the indeterminate clinical form or to the cardiac and/or digestive forms when clinical symptoms are apparent. The relationship between monocytes and lymphocytes may be an important point to help clarify the complexity that surrounds the clinical symptoms of the chronic phase of Chagas disease. The co-stimulatory signals are essential to determining the magnitude of T cell response to the antigen. The signals are known to determine the regulation of subsequent adaptive immune response. However, little is known about the expression and function of these molecules in Chagas disease. Therefore, this review aims to discuss the possible role of main pathways of co-stimulatory molecule-receptor interactions in this pathology that could be crucial to understand the disease dynamics.

Glycogen synthase kinase 3 inhibition lowers PD-1 expression, promotes long-term survival and memory generation in antigen-specific CAR-T cells

Successful remission in hematological cancers by CAR-T cell immunotherapy has yet to be replicated in solid tumors like GBM. A significant impediment of CAR-T immunotherapy in solid tumors is poor exposure of T cells to tumor antigens resulting in suboptimal CAR-T cell activation, which ultimately fails to induce a robust anti-tumor immune response. Costimulatory moieties in advanced-generation CARs, along with additional IL2 therapy has been shown to be insufficient to overcome this hurdle and have its cytotoxic limitations. GSK3 is constitutively active in naïve T cells and is transiently inactivated during T cell activation resulting in rapid T cell proliferation. Pharmacologic inhibition of GSK3 in GBM-specific CAR-T cells reduced FasL expression, increased T cell proliferation and reduced exhaustion by lowering PD-1 levels resulting in the development of CAR-T effector memory phenotype. Treatment with GSK3-inhibited CAR-T cells resulted in 100% tumor elimination during the tumor-rechallenge experiment in GBM-bearing animals and increased accumulation of memory CAR-T cells in secondary lymphoid organs. These adjuvant-like effects of GSK3 inhibition on activated CAR-T cells may be a valuable adjunct to a successful implementation of CAR-T immunotherapy against GBM and other solid tumors.

Protein-Scaffold Directed Nanoscale Assembly of T Cell Ligands: Artificial Antigen Presentation with Defined Valency, Density, and Ratio

Tuning antigen presentation to T cells is a critical step in investigating key aspects of T cell activation. However, existing technologies have a limited ability to control the spatial and stoichiometric organization of T cell ligands on 3D surfaces. Here, we developed an artificial antigen presentation platform based on protein scaffold-directed assembly that allows fine control over the spatial and stoichiometric organization of T cell ligands on a 3D yeast cell surface. Using this system, we observed that the T cell activation threshold on a 3D surface is independent of peptide-major histocompatibility complex (pMHC) valency but instead is determined by the overall pMHC surface density. When intercellular adhesion molecule 1 (ICAM-1) was coassembled with pMHC, it enhanced antigen recognition sensitivity by 6-fold. Further, T cells responded with different magnitudes to varying ratios of pMHC and ICAM-1 and exhibited a maximum response at a ratio of 15% pMHC and 85% ICAM-1, introducing an additional parameter for tuning T cell activation. This protein scaffold-directed assembly technology is readily transferrable to acellular surfaces for translational research as well as large-scale T-cell manufacturing.

LFA-1 in T Cell Migration and Differentiation

Maintenance of homeostatic immune surveillance and development of effective adaptive immune responses require precise regulation of spatial and temporal lymphocyte trafficking throughout the body to ensure pathogen clearance and memory generation. Dysregulation of lymphocyte activation and migration can lead to impaired adaptive immunity, recurrent infections, and an array of autoimmune diseases and chronic inflammation. Central to the recruitment of T cells, integrins are cell surface receptors that regulate adhesion, signal transduction, and migration. With 24 integrin pairs having been discovered to date, integrins are defined not only by the composition of the heterodimeric pair but by cell-type specific expression and their ligands. Furthermore, integrins not only facilitate adhesion but also induce intracellular signaling and have recently been uncovered as mechanosensors providing additional complexity to the signaling pathways. Among several leukocyte-specific integrins, lymphocyte function-associated antigen-1 (LFA-1 or α_Lβ₂; CD11a/CD18) is a key T cell integrin, which plays a major role in regulating T cell activation and migration. Adhesion to LFA-1's ligand, intracellular adhesion receptor 1 (ICAM-1) facilitates firm endothelium adhesion, prolonged contact with antigen-presenting cells, and binding to target cells for killing. While the downstream signaling pathways utilized by LFA-1 are vastly conserved they allow for highly disparate responses. Here, we summarize the roles of LFA-1 and ongoing studies to better understand its functions and regulation.

Developmental endothelial locus-1 (Del-1) antagonizes Interleukin-17-mediated allergic asthma

Interleukin (IL)-17 is a major contributor to the pathogenesis of allergic asthma. Developmental endothelial locus-1 (Del-1) is an endothelial cell-secreted protein known to inhibit IL-17 expression. However, little is known about the association between Del-1 and IL-17 in the pathogenesis of allergic asthma. Using bronchoalveolar lavage fluid (BALF) and peripheral blood samples collected from allergic asthmatic patients and controls, we explored the role of Del-1 in relation to IL-17 in allergic asthma. We found that the negative correlation between Del-1 and IL-17 was significant in BALF of allergic asthmatics. Del-1 treatment inhibited the expression of IL-17, the differentiation of IL-17-secreting leukocytes and associated cytokines. Contrarily, IL-17 levels were increased after treatment with anti-Del-1 mAb. Consistent with this, Del-1 treatment led to downregulation of IL-5, CCL5 and IL-4, thus reducing secretion of eosinophil cationic protein. Furthermore, Del-1 significantly downregulated the expression of ICAM-1 and may have the potential to reduce leukocyte transendothelial migration. Our data demonstrate that Del-1 can negatively regulate IL-17 and its proinflammatory function, thereby limiting airway inflammation in allergic asthmatics, and suggest Del-1 as a potential candidate for prevention and treatment of allergic asthma.

Integrins Modulate T Cell Receptor Signaling by Constraining Actin Flow at the Immunological Synapse

Full T cell activation requires coordination of signals from multiple receptor–ligand pairs that interact in parallel at a specialized cell–cell contact site termed the immunological synapse (IS). Signaling at the IS is intimately associated with actin dynamics; T cell receptor (TCR) engagement induces centripetal flow of the T cell actin network, which in turn enhances the function of ligand-bound integrins by promoting conformational change. Here, we have investigated the effects of integrin engagement on actin flow, and on associated signaling events downstream of the TCR. We show that integrin engagement significantly decelerates centripetal flow of the actin network. In primary CD4⁺ T cells, engagement of either LFA-1 or VLA-4 by their respective ligands ICAM-1 and VCAM-1 slows actin flow. Slowing is greatest when T cells interact with low mobility integrin ligands, supporting a predominately drag-based mechanism. Using integrin ligands presented on patterned surfaces, we demonstrate that the effects of localized integrin engagement are distributed across the actin network, and that focal adhesion proteins, such as talin, vinculin, and paxillin, are recruited to sites of integrin engagement. Further analysis shows that talin and vinculin are interdependent upon one another for recruitment, and that ongoing actin flow is required. Suppression of vinculin or talin partially relieves integrin-dependent slowing of actin flow, indicating that these proteins serve as molecular clutches that couple engaged integrins to the dynamic actin network. Finally, we found that integrin-dependent slowing of actin flow is associated with reduction in tyrosine phosphorylation downstream of the TCR, and that this modulation of TCR signaling depends on expression of talin and vinculin. More generally, we found that integrin-dependent effects on actin retrograde flow were strongly correlated with effects on TCR signaling. Taken together, these studies support a model in which ligand-bound integrins engage the actin cytoskeletal network via talin and vinculin, and tune TCR signaling events by modulating actin dynamics at the IS.

Role of LFA-1 and ICAM-1 in Cancer

The lymphocyte function-associated antigen-1 (LFA-1) (also known as CD11a/CD18 and α_Lβ₂), is just one of many integrins in the human body, but its significance is derived from its exclusive presence in leukocytes. In this review, we summarize the studies relating LFA-1 and its major ligand ICAM-1 (or CD54) with cancer, through the function of lymphocytes and myeloid cells on tumor cells. We consider how LFA-1 mediates the interaction of leukocytes with tumors and the role of ICAM-1 in tumor dynamics, which can be independent of its interaction with LFA-1. We also offer a more detailed examination of the role of LFA-1 within B-cell chronic lymphocytic leukemia. Finally, we discuss the role that exosomes harboring LFA-1 play in tumor growth and metastasis.

Down-regulation of Notch signaling pathway reverses the Th1/Th2 imbalance in tuberculosis patients

Th1/Th2 imbalance to Th2 is of significance in the peripheral immune responses in Tuberculosis (TB) development. However, the mechanisms for Th1/Th2 imbalance are still not well determined. Notch signaling pathway is involved in the peripheral T cell activation and effector cell differentiation. However, whether it affects Th1/Th2 imbalance in TB patients is still not known. Here, we used γ-secretase inhibitor (DAPT) to treat the peripheral blood mononuclear cells (PBMCs) from healthy people or individuals with latent or active TB infection in vitro, respectively. Then, the Th1/Th2 ratios were determined by flow cytometry, and cytokines of IFN-γ, IL-4, IL-10 in the culture supernatant were measured by CBA method. The Notch signal pathway associated proteins Hes1, GATA3 and T-bet were quantitated by real-time PCR or immunoblotting. Our results showed that DAPT effectively inhibited the protein level of Hes1. In TB patients, the Th2 ratio increased in the PBMCs, alone with the high expression of GATA3 and IL-4, resulting in the high ratios of Th2/Th1 and GATA3/T-bet in TB patients. However, Th2 cells ratio decreased after blocking the Notch signaling pathway by DAPT and the Th2/Th1 ratio in TB patients were DAPT dose-dependent, accompanied by the decrease of IL-4 and GATA3. But, its influence on Th1 ratio and Th1 related T-bet and IFN-γ levels were not significant. In conclusion, our results suggest that blocking Notch signaling by DAPT could inhibit Th2 responses and restore Th1/Th2 imbalance in TB patients.

Not Just an Adhesion Molecule: LFA-1 Contact Tunes the T Lymphocyte Program

The α_Lβ₂ integrin LFA-1 is known to play a key role in T lymphocyte migration, which is necessary to mount a local immune response, and is also the main driver of autoimmune diseases. This migration-triggering signaling process in T cells is tightly regulated to permit an immune response that is appropriate to the local trigger, as well as to prevent deleterious tissue-damaging bystander effects. Emerging evidence shows that, in addition to prompting a diverse range of downstream signaling cascades, LFA-1 stimulation in T lymphocytes modulates gene-transcription programs, including genetic signatures of TGF-β and Notch pathways, with multifactorial biological outcomes. This review highlights recent findings and discusses molecular mechanisms by which LFA-1 signaling influence T lymphocyte differentiation into the effector subsets Th1, Th17, and induced regulatory T cells. We argue that LFA-1 contact with a cognate ligand, such as ICAM-1, independent of the immune synapse activates a late divergence in T cells' effector phenotypes, hence fine-tuning their functioning.

G-CSF inhibits LFA-1-mediated CD4+ T cell functions by inhibiting Lck and ZAP-70

In this study, we showed that G-CSF mobilization increased the frequency of T cells, specifically CD3⁺CD4⁺ T cells. G-CSF mobilization decreased the secretion of inflammatory cytokines of CD4⁺ T cells through the LFA-1/ICAM-1 signaling pathway, whereas it did not alter the TH1/TH2 ratio. We found that G-CSF mobilization inhibited LFA-1-mediated CD4⁺ T cell polarization and motility. In vitro, G-CSF stimulation also attenuated the polarization and adhesiveness of CD4⁺ T cells through the LFA-1/ICAM-1 interaction. Further investigation revealed that G-CSF mobilization suppressed LFA-1 signaling by down-regulating Lck and ZAP-70 expression in CD4⁺ T cells, similar results was also confirmed by in-vitro studies. These findings suggested that G-CSF directly suppressed LFA-1-mediated CD4⁺ T cell functions through the down-regulation of Lck and ZAP-70. The immunosuppressive effect of G-CSF mobilization deepened our understanding about peripheral blood hematopoietic stem cell transplantation. LFA-1/ICMA-1 pathway may become a potential target for graft-versus-host disease prophylaxis.

Association of Ribonuclease T2 Gene Polymorphisms With Decreased Expression and Clinical Characteristics of Severity in Crohn's Disease

BACKGROUND & AIMS

Variants in the tumor necrosis factor superfamily member 15 gene (TNFSF15, also called TL1A) have been associated with risk for inflammatory bowel disease (IBD). TL1A affects expression of multiple cytokines to promote mucosal inflammation. Little is known about the TL1A-response pathways that regulate cytokine expression. We investigated T-cell gene expression patterns to determine the mechanisms by which TL1A regulates cytokine production, and whether these associate with outcomes of patients with Crohn's disease (CD).

METHODS

Peripheral T cells isolated from normal donors were cultured with TL1A. We performed gene expression profile analysis by RNA sequencing of subsets of interferon gamma (IFNG)-producing and non-producing cells purified by flow cytometry. Unsupervised hierarchical clustering analysis was used to identify gene expression differences between these subsets. Ribonuclease T2 gene (RNASET2) expression and methylation were assessed by quantitative trait loci analyses. Clinical characteristics of patients (complications, resistance to therapy, and recurrence time) were associated with single nucleotide polymorphisms in RNASET2. We performed motif screening to identify polymorphisms that disrupt transcription factor binding sites. Levels of RNASET2 were knocked down with small interfering RNA in CD4⁺ T cells and the effect on protein expression was determined by proteomic analysis and cytokine production. Cell aggregation was measured by flow cytometry.

RESULTS

We identified 764 genes with at least a 2-fold difference in TL1A-mediated expression between IFNG-secreting and non-secreting T cells (P < 1 × 10^-5). Many of these genes were located near IBD susceptibility variants. RNASET2 was the only IBD risk-associated gene with >5-fold down-regulation in the IFNG-secreting subset. RNASET2 disease risk variants were associated with decreased expression in peripheral and mucosal tissues and DNA hypermethylation in CD patients requiring surgical intervention. RNASET2 disease risk variants were associated in CD patients with more complicated disease or resistance to therapy, defined in part by failed response to treatment, increased length of intestinal resection, shorter time to repeat surgery, and high Rutgeerts score (>2) in postoperative endoscopy. The RNASET2 variant rs2149092 was predicted to disrupt a consensus binding site for the transcription factor ETS within an enhancer region. Expression of RNASET2 correlated with expression of ETS. RNASET2 knockdown in T cells increased expression of IFNG and intercellular adhesion molecule 1 (ICAM1) and induced T-cell aggregation. A blocking antibody against (ILFA1), disrupting the lymphocyte function-associated antigen 1-intercellular adhesion molecule 1 interaction, reduced T-cell production of IFNG.

CONCLUSIONS

We identified decreased expression of RNASET2 as a component of TL1A-mediated increase in production of IFNG and as a potential biomarker for patients with severe CD. Further study of the role of RNASET2 in regulating mucosal inflammation may lead to development of novel therapeutic targets.

Dysregulated CD46 shedding interferes with Th1-contraction in systemic lupus erythematosus

IFN‐γ‐producing T helper 1 (Th1) cell responses mediate protection against infections but uncontrolled Th1 activity also contributes to a broad range of autoimmune diseases. Autocrine complement activation has recently emerged as key in the induction and contraction of human Th1 immunity: activation of the complement regulator CD46 and the C3aR expressed by CD4⁺ T cells via autocrine generated ligands C3b and C3a, respectively, are critical to IFN‐γ production. Further, CD46‐mediated signals also induce co‐expression of immunosuppressive IL‐10 in Th1 cells and transition into a (self)‐regulating and contracting phase. In consequence, C3 or CD46‐deficient patients suffer from recurrent infections while dysregulation of CD46 signaling contributes to Th1 hyperactivity in rheumatoid arthritis and multiple sclerosis. Here, we report a defect in CD46‐regulated Th1 contraction in patients with systemic lupus erythematosus (SLE). We observed that MMP‐9‐mediated increased shedding of soluble CD46 by Th1 cells was associated with this defect and that inhibition of MMP‐9 activity normalized release of soluble CD46 and restored Th1 contraction in patients’ T cells. These data may deliver the first mechanistic explanation for the increased serum CD46 levels observed in SLE patients and indicate that targeting CD46‐cleaving proteases could be a novel avenue to modulate Th1 responses.