Tumor-derived GCSF Alters Tumor and Systemic Immune System Cell Subset Composition and Signaling

While immunotherapies such as immune checkpoint blockade and adoptive T-cell therapy improve survival for a subset of human malignancies, many patients fail to respond. Phagocytes including dendritic cells (DC), monocytes, and macrophages (MF) orchestrate innate and adaptive immune responses against tumors. However, tumor-derived factors may limit immunotherapy effectiveness by altering phagocyte signal transduction, development, and activity. Using Cytometry by Time-of-Flight, we found that tumor-derived GCSF altered myeloid cell distribution both locally and systemically. We distinguished a large number of GCSF-induced immune cell subset and signal transduction pathway perturbations in tumor-bearing mice, including a prominent increase in immature neutrophil/myeloid-derived suppressor cell (Neut/MDSC) subsets and tumor-resident PD-L1⁺ Neut/MDSCs. GCSF expression was also linked to distinct tumor-associated MF populations, decreased conventional DCs, and splenomegaly characterized by increased splenic progenitors with diminished DC differentiation potential. GCSF-dependent dysregulation of DC development was recapitulated in bone marrow cultures in vitro, using medium derived from GCSF-expressing tumor cell cultures. Importantly, tumor-derived GCSF impaired T-cell adoptive cell therapy effectiveness and was associated with increased tumor volume and diminished survival of mice with mammary cancer. Treatment with neutralizing anti-GCSF antibodies reduced colonic and circulatory Neut/MDSCs, normalized colonic immune cell composition and diminished tumor burden in a spontaneous model of mouse colon cancer. Analysis of human colorectal cancer patient gene expression data revealed a significant correlation between survival and low GCSF and Neut/MDSC gene expression. Our data suggest that normalizing GCSF bioactivity may improve immunotherapy in cancers associated with GCSF overexpression.

Significance

Tumor-derived GCSF leads to systemic immune population changes. GCSF blockade restores immune populations, improves immunotherapy, and reduces tumor size, paralleling human colorectal cancer data. GCSF inhibition may synergize with current immunotherapies to treat GCSF-secreting tumors.

Highly Sensitive, Flow Cytometry-Based Measurement of Intestinal Permeability in Models of Experimental Colitis

BACKGROUND & AIMS

Increased intestinal permeability is seen in a variety of inflammatory conditions such as enteric infections and inflammatory bowel disease. Because barrier function can provide a key biomarker of disease severity, it often is assayed in animal models. A common methodology involves gavaging mice with fluorescein isothiocyanate-conjugated dextran (FITC-D), followed by cardiac puncture to assay plasma fluorescence on a spectrophotometer. Although the FITC-D method is relatively simple, its sensitivity is limited and enables only a single measurement because the test requires killing the subject. Herein, we describe a novel flow cytometry-based method of intestinal permeability measurement based on detection of orally gavaged ovalbumin (OVA) that leaks out of the gut. Our approach uses minute blood volumes collected from the tail vein, permitting repeated testing of the same subject at multiple time points. By comparing this assay against the gold standard FITC-D method, we show the expanded utility of our OVA assay in measuring intestinal permeability.

METHODS

We directly compared our OVA assay against the FITC-D assay by co-administering both probes orally to the same animals and subsequently using their respective methodologies to measure intestinal permeability by detecting probe levels in the plasma. Permeability was assessed in mice genetically deficient in intestinal mucus production or glycosylation. In addition, wild-type mice undergoing dextran sodium sulfate-induced colitis or infected by the enteric bacterial pathogen Citrobacter rodentium also were tested.

RESULTS

The OVA assay showed very high efficacy in all animal models of intestinal barrier dysfunction tested. Besides identifying intestinal barrier dysfunction in mice with impaired mucin glycosylation, the assay also allowed for repeated tracking of intestinal permeability within the same animal over time, providing data that cannot be easily acquired with other currently applied methods.

CONCLUSIONS

The OVA assay is a highly sensitive and effective method of measuring intestinal permeability in mouse models of barrier dysfunction and experimental colitis.

Human JAK1 gain of function causes dysregulated myelopoeisis and severe allergic inflammation

Primary atopic disorders are a group of inborn errors of immunity that skew the immune system toward severe allergic disease. Defining the biology underlying these extreme monogenic phenotypes reveals shared mechanisms underlying common polygenic allergic disease and identifies potential drug targets. Germline gain-of-function (GOF) variants in JAK1 are a cause of severe atopy and eosinophilia. Modeling the JAK1GOF (p.A634D) variant in both zebrafish and human induced pluripotent stem cells (iPSCs) revealed enhanced myelopoiesis. RNA-Seq of JAK1GOF human whole blood, iPSCs, and transgenic zebrafish revealed a shared core set of dysregulated genes involved in IL-4, IL-13, and IFN signaling. Immunophenotypic and transcriptomic analysis of patients carrying a JAK1GOF variant revealed marked Th cell skewing. Moreover, long-term ruxolitinib treatment of 2 children carrying the JAK1GOF (p.A634D) variant remarkably improved their growth, eosinophilia, and clinical features of allergic inflammation. This work highlights the role of JAK1 signaling in atopic immune dysregulation and the clinical impact of JAK1/2 inhibition in treating eosinophilic and allergic disease.

The Role of Autoimmunity-Related Gene CLEC16A in the B Cell Receptor-Mediated HLA Class II Pathway

C-type lectin CLEC16A is located next to CIITA, the master transcription factor of HLA class II (HLA-II), at a susceptibility locus for several autoimmune diseases, including multiple sclerosis (MS). We previously found that CLEC16A promotes the biogenesis of HLA-II peptide-loading compartments (MIICs) in myeloid cells. Given the emerging role of B cells as APCs in these diseases, in this study, we addressed whether and how CLEC16A is involved in the BCR-dependent HLA-II pathway. CLEC16A was coexpressed with surface class II-associated invariant chain peptides (CLIP) in human EBV-positive and not EBV-negative B cell lines. Stable knockdown of CLEC16A in EBV-positive Raji B cells resulted in an upregulation of surface HLA-DR and CD74 (invariant chain), whereas CLIP was slightly but significantly reduced. In addition, IgM-mediated Salmonella uptake was decreased, and MIICs were less clustered in CLEC16A-silenced Raji cells, implying that CLEC16A controls both HLA-DR/CD74 and BCR/Ag processing in MIICs. In primary B cells, CLEC16A was only induced under CLIP-stimulating conditions in vitro and was predominantly expressed in CLIP^high naive populations. Finally, CLIP-loaded HLA-DR molecules were abnormally enriched, and coregulation with CLEC16A was abolished in blood B cells of patients who rapidly develop MS. These findings demonstrate that CLEC16A participates in the BCR-dependent HLA-II pathway in human B cells and that this regulation is impaired during MS disease onset. The abundance of CLIP already on naive B cells of MS patients may point to a chronically induced stage and a new mechanism underlying B cell-mediated autoimmune diseases such as MS.

Cutting Edge: Intestinal Mucus Limits the Clonal Deletion of Developing T Cells Specific for an Oral Antigen

A layer of mucus functions to segregate contents of the intestinal lumen from the intestinal epithelium. The MUC2 mucin is the primary constituent of intestinal mucus and plays critical protective roles against luminal microbes and other noxious agents. In this study, we investigated whether MUC2 helps maintain CD8 T cell tolerance toward intestinal luminal Ags by gavaging wild-type and Muc2^-/- mice with a model Ag and monitoring immune responses posttreatment. We report that orally delivered OVA rapidly disseminates through the blood of Muc2^-/- (but not control) mice and causes immune activation of Ag-specific CD8 T cells at both local and distal sites. Further, the administration of oral OVA to Muc2^-/- mice led to its presentation by thymic dendritic cells and the deletion of Ag-specific thymocytes. Collectively, our findings suggest that intestinal mucus helps limit the shaping of the TCR repertoire of developing thymocytes by intestinal luminal Ags.

Deep Phenotyping by Mass Cytometry and Single-Cell RNA-Sequencing Reveals LYN-Regulated Signaling Profiles Underlying Monocyte Subset Heterogeneity and Lifespan

RATIONALE

Monocytes are key effectors of the mononuclear phagocyte system, playing critical roles in regulating tissue homeostasis and coordinating inflammatory reactions, including those involved in chronic inflammatory diseases such as atherosclerosis. Monocytes have traditionally been divided into 2 major subsets termed conventional monocytes and patrolling monocytes (pMo) but recent systems immunology approaches have identified marked heterogeneity within these cells, and much of what regulates monocyte population homeostasis remains unknown. We and others have previously identified LYN tyrosine kinase as a key negative regulator of myeloid cell biology; however, LYN's role in regulating specific monocyte subset homeostasis has not been investigated.

OBJECTIVE

We sought to comprehensively profile monocytes to elucidate the underlying heterogeneity within monocytes and dissect how Lyn deficiency affects monocyte subset composition, signaling, and gene expression. We further tested the biological significance of these findings in a model of atherosclerosis.

METHODS AND RESULTS

Mass cytometric analysis of monocyte subsets and signaling pathway activation patterns in conventional monocytes and pMos revealed distinct baseline signaling profiles and far greater heterogeneity than previously described. Lyn deficiency led to a selective expansion of pMos and alterations in specific signaling pathways within these cells, revealing a critical role for LYN in pMo physiology. LYN's role in regulating pMos was cell-intrinsic and correlated with an increased circulating half-life of Lyn-deficient pMos. Furthermore, single-cell RNA sequencing revealed marked perturbations in the gene expression profiles of Lyn^-/- monocytes with upregulation of genes involved in pMo development, survival, and function. Lyn deficiency also led to a significant increase in aorta-associated pMos and protected Ldlr^-/- mice from high-fat diet-induced atherosclerosis.

CONCLUSIONS

Together our data identify LYN as a key regulator of pMo development and a potential therapeutic target in inflammatory diseases regulated by pMos.

Arp2/3 complex-driven spatial patterning of the BCR enhances immune synapse formation, BCR signaling and B cell activation

When B cells encounter antigens on the surface of an antigen-presenting cell (APC), B cell receptors (BCRs) are gathered into microclusters that recruit signaling enzymes. These microclusters then move centripetally and coalesce into the central supramolecular activation cluster of an immune synapse. The mechanisms controlling BCR organization during immune synapse formation, and how this impacts BCR signaling, are not fully understood. We show that this coalescence of BCR microclusters depends on the actin-related protein 2/3 (Arp2/3) complex, which nucleates branched actin networks. Moreover, in murine B cells, this dynamic spatial reorganization of BCR microclusters amplifies proximal BCR signaling reactions and enhances the ability of membrane-associated antigens to induce transcriptional responses and proliferation. Our finding that Arp2/3 complex activity is important for B cell responses to spatially restricted membrane-bound antigens, but not for soluble antigens, highlights a critical role for Arp2/3 complex-dependent actin remodeling in B cell responses to APC-bound antigens.

Prevention of autoimmune diabetes and islet allograft rejection by beta cell expression of XIAP: Insight into possible mechanisms of local immunomodulation

Overexpression of the X-linked inhibitor of apoptosis (XIAP) prevents islet allograft rejection. We constructed an adeno-associated virus expressing XIAP driven by the rat insulin promoter (dsAAV8-RIP-XIAP) for long-term beta-cell gene expression in vivo. Pancreatic delivery of dsAAV8-RIP-XIAP prevented autoimmune diabetes in 70% of non-obese diabetic (NOD) mice, associated with decreased insulitis. Islets from Balb/c mice transduced with dsAAV8-RIP-XIAP were protected following transplantation into streptozotocin (STZ)-diabetic Bl/6 recipients, associated with decreased graft infiltration. Interestingly, dsAAV8-RIP-XIAP transduction induced expression of lactate dehydrogenase (LDHA) and monocarboxylate transporter 1 (MCT1), two genes normally suppressed in beta cells and involved in production and release of lactate, a metabolite known to suppress local immune responses. Transduction of Balb/c islets with AAV8-RIP-LDHA-MCT1 tended to prolong allograft survival following transplant into STZ-diabetic Bl/6 recipients. These findings suggest that XIAP has therapeutic potential in autoimmune diabetes and raise the possibility that local lactate production may play a role in XIAP-mediated immunomodulation.

2B4-SAP signaling is required for the priming of naive CD8+ T cells by antigen-expressing B cells and B lymphoma cells

Mutations in SH2D1A gene that encodes SAP (SLAM-associated protein) result in X-linked lymphoproliferative disease (XLP), a rare primary immunodeficiency disease defined by exquisite sensitivity to the B-lymphotropic Epstein-Barr virus (EBV) and B cell lymphomas. However, the precise mechanism of how the loss of SAP function contributes to extreme vulnerability to EBV and the development of B cell lymphomas remains unclear. Here, we investigate the hypothesis that SAP is critical for CD8⁺ T cell immune surveillance of antigen (Ag)-expressing B cells or B lymphoma cells under conditions of defined T cell receptor (TCR) signaling. Sh2d1a^-/- CD8⁺ T cells exhibited greatly diminished proliferation relative to wild type when Ag-presenting-B cells or -B lymphoma cells served as the primary Ag-presenting cell (APC). By contrast, Sh2d1a^-/- CD8⁺ T cells responded equivalently to wild-type CD8⁺ T cells when B cell-depleted splenocytes, melanoma cells or breast carcinoma cells performed Ag presentation. Through application of signaling lymphocyte activation molecule (SLAM) family receptor blocking antibodies or SLAM family receptor-deficient CD8⁺ T cells and APCs, we found that CD48 engagement on the B cell surface by 2B4 is crucial for initiating SAP-dependent signaling required for the Ag-driven CD8⁺ T cell proliferation and differentiation. Altogether, a pivotal role for SAP in promoting the expansion and differentiation of B cell-primed viral-specific naive CD8⁺ T cells may explain the selective immune deficiency of XLP patients to EBV and B cell lymphomas.

CCL22 Prevents Rejection of Mouse Islet Allografts and Induces Donor-Specific Tolerance

Manipulation of regulatory T cell (Treg) migration by islet expression of the chemokine CCL22 prevents diabetes in NOD mice and delays recurrent autoimmunity in syngeneic islet transplants. We sought to determine whether attracting Tregs with CCL22 also prevents islet allograft rejection. Isolated Bl/6 mouse islets were transduced overnight with adenovirus expressing CCL22 (Ad-CCL22) downstream of the CMV promoter. Islets were transplanted under the renal capsule of Balb/c recipients made diabetic by streptozotocin. To assess immunologic tolerance, graft-bearing kidneys from recipients of CCL22-expressing islet grafts were removed, and mice received a second transplant of naive islets from the same donor strain or third-party islets into the contralateral kidney. Adenoviral expression of CCL22 conferred prolonged protection of islet allografts in MHC-mismatched, diabetic recipients, maintaining normoglycemia in 75% of recipients for at least 80 days. Increased frequency of Treg cells was observed in islet grafts transduced with Ad-CCL22 compared with untreated grafts. Normoglycemic recipients of CCL22-expressing islet grafts showed complete absence of antidonor antibodies and no lymphocyte proliferation after exposure to donor splenocytes. After removal of the primary graft at day 80, mice that received a second transplant with untreated islets from the same donor strain did not reject the grafts, suggesting the development of tolerance. Expression of CCL22 recruits Treg cells to transplanted islets, prevents activation of alloreactive T-cells and islet allograft failure and induces alloantigen-specific tolerance. Manipulation of Treg cells by CCL22 in transplanted islets may be a novel therapeutic strategy for diabetes.

Dual T cell receptor-expressing CD8 T cells potentiate autoreactivity

Central tolerance serves to eliminate newly developing T cells that express strongly autoreactive T cell receptors. Although central tolerance is efficient in deleting high avidity autoreactive T cells, some lower avidity autoreactive T cells escape negative selection to cause autoimmune diseases. Although tight allelic exclusion limits thymocytes to expressing a single TCRbeta chain, rearrangement of the TCRalpha chain continues unabated until halted by positive selection, enabling thymocytes to express up to two TCRalpha chains and thus two TCRs. Moreover, it has been postulated that pathogenic low avidity autoreactive CD8 T cells may escape central tolerance through expression of a secondary benign TCR that mediates positive selection. To determine the role of dual TCR expressing CD8 T cells in autoreactivity and autoimmunity, we have compared CD8 T cell autoreactivity against the model autoantigen ovalbumin between T cells capable of expressing two TCRs (TCRalpha+/+) versus T cells capable of expressing a single TCR (TCRalpha+/−). TCRalpha+/− CD8 T cells exhibited reduced proliferative capacity upon OVA stimulation relative to TCRalpha+/+ CD8 T cells. In addition, a lower frequency of TCRalpha+/− CD8 T cell effectors produced IFN-gamma upon activation with OVA compared to TCRalpha+/+ CD8 T cell effectors. Taken together, we shown that dual TCR expression by CD8 T cells reduces the efficiency of T cell tolerance and may potentiate T cell autoreactivity. We are investigating whether dual TCR-expressing T cells are key to the pathogenesis of autoimmune diabetes in our mouse model system. Our results will provide valuable insight into the escape mechanisms exploited by pathogenic autoreactive CD8 T cells.

SLAM family receptors 2B4 and CD48 are key drivers of CD8 T cell priming by B cells

Mutations in SH2D1A gene that encodes SAP (SLAM-associated protein) result in X-linked lymphoproliferative disease (XLP), a rare primary immunodeficiency defined by exquisite sensitivity to the B-lymphotropic Epstein-Barr virus (EBV) and B cell lymphomas. However, the precise mechanism of how the loss of SAP function contributes to extreme vulnerability to EBV and the development of B cell lymphomas remains unclear. Here, we utilized SAP-deficient (Sh2d1a−/−) mice to investigate the hypothesis that SAP is critical for CD8 T cell immune surveillance of antigen-expressing B cells or B lymphoma cells. Sh2d1a−/− CD8 T cells exhibited greatly diminished proliferation relative to wild type when antigen-presenting-B cells or -B lymphoma cells served as the primary APC. By contrast, Sh2d1a−/− CD8 T cells responded equivalently to wild type CD8 T cells when B cell-depleted splenocytes, melanoma cells or breast carcinoma cells performed antigen presentation. Through application of SLAM family receptor blocking antibodies or SLAM family receptor-deficient CD8 T cells and APCs, we found that CD48 engagement on the B cell surface by 2B4 is crucial for initiating SAP-dependent signaling required for the antigen-driven CD8 T cell proliferation and differentiation. Altogether, a pivotal role for SAP in promoting the expansion and differentiation of B cell-primed viral-specific naïve CD8 T cells may explain the selective immune deficiency of XLP patients to EBV and B cell lymphomas.

MALT1-deficient CD4 T cells exhibit decreased IL-2 secretion and impaired Th1 and Th17 differentiation

A child admitted to British Columbia Children’s Hospital displayed a novel clinical presentation of immune dysregulation, exhibiting lymphocytic infiltration and severe inflammation of the intestinal tract and other mucosal surfaces. Whole-exome sequencing revealed that the patient inherited missense MALT1 mutations and her lymphocytes exhibited deficits in MALT1 protein and MALT1-dependent signal transduction. MALT1 plays critical roles in T cell receptor signal transduction through at least two different mechanisms: (1) as a signaling adaptor molecule bringing together CARMA-1 and BCL-10 to form the CBM signalosome complex and (2) as a caspase-like protease (paracaspase) cleaving substrates after arginine residues. Studies on Malt1−/− mice have revealed diminished NF-KB activation and weakened T cell immunity whereas mice lacking paracaspase activity but not MALT1 adaptor function are prone to lethal autoimmunity. Altogether, these mouse findings raise questions regarding the nature of our patient’s mutant MALT1 protein and the role it plays in her proinflammatory phenotype. Consequently, we plan to analyze our patient’s MALT1 mutation by investigating the paracaspase activity, signaling, and function of her T cells. Early studies have found that patient CD4 T cells exhibit defects in Th1 and Th17 differentiation and these impairments could be responsible for inefficient immune responses leading to chronic infections. Finally, a better understanding of MALT1 will provide insight into inflammatory disease and prove invaluable in supporting MALT1-targeted therapies to modulate T cells to treat autoimmune diseases.

The paracaspase MALT1 cleaves HOIL1 reducing linear ubiquitination by LUBAC to dampen lymphocyte NF-κB signalling

Antigen receptor signalling activates the canonical NF-κB pathway via the CARD11/BCL10/MALT1 (CBM) signalosome involving key, yet ill-defined roles for linear ubiquitination. The paracaspase MALT1 cleaves and removes negative checkpoint proteins, amplifying lymphocyte responses in NF-κB activation and in B-cell lymphoma subtypes. To identify new human MALT1 substrates, we compare B cells from the only known living MALT1(mut/mut) patient with healthy MALT1(+/mut) family members using 10-plex Tandem Mass Tag TAILS N-terminal peptide proteomics. We identify HOIL1 of the linear ubiquitin chain assembly complex as a novel MALT1 substrate. We show linear ubiquitination at B-cell receptor microclusters and signalosomes. Late in the NF-κB activation cycle HOIL1 cleavage transiently reduces linear ubiquitination, including of NEMO and RIP1, dampening NF-κB activation and preventing reactivation. By regulating linear ubiquitination, MALT1 is both a positive and negative pleiotropic regulator of the human canonical NF-κB pathway-first promoting activation via the CBM--then triggering HOIL1-dependent negative-feedback termination, preventing reactivation.

CD1d Expression and Invariant NKT Cell Responses in Herpesvirus Infections

Invariant natural killer T (iNKT) cells are a highly conserved subset of unconventional T lymphocytes that express a canonical, semi-invariant T cell receptor and surface markers shared with the natural killer cell lineage. iNKT cells recognize exogenous and endogenous glycolipid antigens restricted by non-polymorphic CD1d molecules, and are highly responsive to the prototypical agonist, α-galactosylceramide. Upon activation, iNKT cells rapidly coordinate signaling between innate and adaptive immune cells through the secretion of proinflammatory cytokines, leading to the maturation of antigen-presenting cells, and expansion of antigen-specific CD4+ and CD8+ T cells. Because of their potent immunoregulatory properties, iNKT cells have been extensively studied and are known to play a pivotal role in mediating immune responses against microbial pathogens including viruses. Here, we review evidence that herpesviruses manipulate CD1d expression to escape iNKT cell surveillance and establish lifelong latency in humans. Collectively, published findings suggest that iNKT cells play critical roles in anti-herpesvirus immune responses and could be harnessed therapeutically to limit viral infection and viral-associated disease.

Multiple sclerosis-associated CLEC16A controls HLA class II expression via late endosome biogenesis

C-type lectins are key players in immune regulation by driving distinct functions of antigen-presenting cells. The C-type lectin CLEC16A gene is located at 16p13, a susceptibility locus for several autoimmune diseases, including multiple sclerosis. However, the function of this gene and its potential contribution to these diseases in humans are poorly understood. In this study, we found a strong upregulation of CLEC16A expression in the white matter of multiple sclerosis patients (n = 14) compared to non-demented controls (n = 11), mainly in perivascular leukocyte infiltrates. Moreover, CLEC16A levels were significantly enhanced in peripheral blood mononuclear cells of multiple sclerosis patients (n = 69) versus healthy controls (n = 46). In peripheral blood mononuclear cells, CLEC16A was most abundant in monocyte-derived dendritic cells, in which it strongly co-localized with human leukocyte antigen class II. Treatment of these professional antigen-presenting cells with vitamin D, a key protective environmental factor in multiple sclerosis, downmodulated CLEC16A in parallel with human leukocyte antigen class II. Knockdown of CLEC16A in distinct types of model and primary antigen-presenting cells resulted in severely impaired cytoplasmic distribution and formation of human leucocyte antigen class II-positive late endosomes, as determined by immunofluorescence and electron microscopy. Mechanistically, CLEC16A participated in the molecular machinery of human leukocyte antigen class II-positive late endosome formation and trafficking to perinuclear regions, involving the dynein motor complex. By performing co-immunoprecipitations, we found that CLEC16A directly binds to two critical members of this complex, RILP and the HOPS complex. CLEC16A silencing in antigen-presenting cells disturbed RILP-mediated recruitment of human leukocyte antigen class II-positive late endosomes to perinuclear regions. Together, we identify CLEC16A as a pivotal gene in multiple sclerosis that serves as a direct regulator of the human leukocyte antigen class II pathway in antigen-presenting cells. These findings are a first step in coupling multiple sclerosis-associated genes to the regulation of the strongest genetic factor in multiple sclerosis, human leukocyte antigen class II.

Lyn deficiency leads to increased microbiota-dependent intestinal inflammation and susceptibility to enteric pathogens

The Lyn tyrosine kinase governs the development and function of various immune cells, and its dysregulation has been linked to malignancy and autoimmunity. Using models of chemically induced colitis and enteric infection, we show that Lyn plays a critical role in regulating the intestinal microbiota and inflammatory responses as well as protection from enteric pathogens. Lyn(-/-) mice were highly susceptible to dextran sulfate sodium (DSS) colitis, characterized by significant wasting, rectal bleeding, colonic pathology, and enhanced barrier permeability. Increased DSS susceptibility in Lyn(-/-) mice required the presence of T but not B cells and correlated with dysbiosis and increased IFN-γ(+) and/or IL-17(+) colonic T cells. This dysbiosis was characterized by an expansion of segmented filamentous bacteria, associated with altered intestinal production of IL-22 and IgA, and was transmissible to wild-type mice, resulting in increased susceptibility to DSS. Lyn deficiency also resulted in an inability to control infection by the enteric pathogens Salmonella enterica serovar Typhimurium and Citrobacter rodentium. Lyn(-/-) mice exhibited profound cecal inflammation, bacterial dissemination, and morbidity following S. Typhimurium challenge and greater colonic inflammation throughout the course of C. rodentium infection. These results identify Lyn as a key regulator of the mucosal immune system, governing pathophysiology in multiple models of intestinal disease.

SLAM-SAP signaling promotes differentiation of IL-17-producing T cells and progression of experimental autoimmune encephalomyelitis

IL-17 plays critical roles in host defenses, combating bacterial and fungal infections, as well as the pathogenesis of autoimmune diseases such as experimental autoimmune encephalomyelitis (EAE). The signaling adaptor SAP is essential for normal immune homeostasis and mutations within SH2D1A, the locus encoding this protein, result in serious and sometimes fatal syndromes, including X-linked lymphoproliferative disease and severe cases of common variable immunodeficiency. However, the precise cellular basis of how SAP deficiency contributes to immune dysfunction remains incompletely understood. In this study, we found that CD4 and CD8 T cells lacking SAP had a diminished capacity to differentiate into IL-17-producing Th17 and T cytotoxic (Tc17) cells relative to wild-type lymphocytes. The use of costimulating SLAM Abs was found to augment the differentiation of IL-17-secreting effectors in wild-type but not Sh2d1a(-/-) splenic T cells under IL-17-polarizing conditions. In addition, SAP's regulation of IL-17-secreting T cells was shown to be a T cell-intrinsic role, as purified naive Sh2d1a(-/-) CD4 and CD8 T cells were inherently defective at converting into Th17 and Tc17 cells in vitro and in vivo. Furthermore, Sh2d1a(-/-) mice were protected from EAE and exhibited greatly decreased numbers of CNS-infiltrating Th17 and Tc17 effector T cells and reduced disease severity. Collectively, these results suggest that SLAM-SAP signaling drives the differentiation and function of Th17 and Tc17 cells in vitro and in vivo and contributes to the pathogenesis of autoimmunity in EAE.

Natural killer T cell strategies to combat Epstein-Barr virus infection

Epstein-Barr virus (EBV) infection results in rapid loss of CD1d expression from the surface of infected B cells, thus enabling the virus to evade immune recognition by natural killer T (NKT) cells. Using pharmacologic means to boost CD1d expression, potent NKT cell effector functions can be elicited toward EBV-infected B cells, suggesting the promise of novel strategies to target EBV-associated diseases such as some B-cell malignancies.

PSGL-1 regulates the migration and proliferation of CD8(+) T cells under homeostatic conditions

P-selectin glycoprotein ligand-1 (PSGL-1), a heavily glycosylated sialomucin expressed on most leukocytes, has dual function as a selectin ligand for leukocyte rolling on vascular selectins expressed in inflammation and as a facilitator of resting T cell homing into lymphoid organs. In this article, we document disturbances in T cell homeostasis present in PSGL-1(null) mice. Naive CD4(+) and CD8(+) T cell frequencies were profoundly reduced in blood, whereas T cell numbers in lymph nodes and spleen were at or near normal levels. Although PSGL-1(null) T cells were less efficient at entering lymph nodes, they also remained in lymph nodes longer than PSGL-1(+/+) T cells, suggesting that PSGL-1 supports T cell egress. In addition, PSGL-1(null) CD8(+) T cell proliferation was observed under steady-state conditions and PSGL-1(null) CD8(+) T cells were found to be hyperresponsive to homeostatic cytokines IL-2, IL-4, and IL-15. Despite these disturbances in T cell homeostasis, PSGL-1(null) mice exhibited a normal acute response (day 8) to lymphocytic choriomeningitis virus infection but generated an increased frequency of memory T cells (day 40). Our observations demonstrate a novel pleiotropic influence of PSGL-1 deficiency on several aspects of T cell homeostasis that would not have been anticipated based on the mild phenotype of PSGL-1(null) mice. These potentially offsetting effects presumably account for the near-normal cellularity seen in lymph nodes of PSGL-1(null) mice.

NKT cells are required for complete Freund's adjuvant-mediated protection from autoimmune diabetes

Autoimmune diabetes in NOD mice can be prevented by application of Ags derived from Mycobacterium tuberculosis in the form of bacillus Calmette-Guérin or CFA. Disease protection by CFA is associated with a reduction in the numbers of pathogenic β-cell specific, self-reactive CTLs, a phenomenon dependent on the presence and function of NK cells. However, the mechanisms by which NK cells are activated and recruited by heat-killed M. tuberculosis within CFA are unclear. In this study, we report that CFA-mediated NK cell activation and mobilization is dependent on CD1d expression. The administration of M. tuberculosis from CFA results in rapid NKT cell activation and IFN-γ secretion both in vitro and in vivo. CFA-induced NKT cell activation is intact in MyD88(-/-) mice suggesting that the mechanism is independent of TLR signaling. Furthermore, CD1d expression was found to be essential for both M. tuberculosis-triggered NKT cell activation and CFA-mediated protection of NOD mice from diabetes. Collectively, these findings reveal hitherto previously unidentified roles for NKT cells in the adjuvant-promoting effects of CFA on innate and adaptive immunity.

Natural killer cells from children with type 1 diabetes have defects in NKG2D-dependent function and signaling

OBJECTIVE

Natural killer (NK) cells from NOD mice have numeric and functional abnormalities, and restoration of NK cell function prevents autoimmune diabetes in NOD mice. However, little is known about the number and function of NK cells in humans affected by type 1 diabetes. Therefore, we evaluated the phenotype and function of NK cells in a large cohort of type 1 diabetic children.

RESEARCH DESIGN AND METHODS

Peripheral blood mononuclear blood cells were obtained from subjects whose duration of disease was between 6 months and 2 years. NK cells were characterized by flow cytometry, enzyme-linked immunosorbent spot assays, and cytotoxicity assays. Signaling through the activating NK cell receptor, NKG2D, was assessed by immunoblotting and reverse-phase phosphoprotein lysate microarray.

RESULTS

NK cells from type 1 diabetic subjects were present at reduced cell numbers compared with age-matched, nondiabetic control subjects and had diminished responses to the cytokines interleukin (IL)-2 and IL-15. Analysis before and after IL-2 stimulation revealed that unlike NK cells from nondiabetic control subjects, NK cells from type 1 diabetic subjects failed to downregulate the NKG2D ligands, major histocompatibility complex class I-related chains A and B, upon activation. Moreover, type 1 diabetic NK cells also exhibited decreased NKG2D-dependent cytotoxicity and interferon-γ secretion. Finally, type 1 diabetic NK cells showed clear defects in NKG2D-mediated activation of the phosphoinositide 3-kinase-AKT pathway.

CONCLUSIONS

These results are the first to demonstrate that type 1 diabetic subjects have aberrant signaling through the NKG2D receptor and suggest that NK cell dysfunction contributes to the autoimmune pathogenesis of type 1 diabetes.

Cutting edge: Increased IL-17-secreting T cells in children with new-onset type 1 diabetes

CD4(+)FOXP3(+) regulatory T cells are essential for immune tolerance, and murine studies suggest that their dysfunction can lead to type 1 diabetes (T1D). Human studies assessing regulatory T cell dysfunction in T1D have relied on analysis of FOXP3-expressing cells. Recently, distinct subsets of CD4(+)FOXP3(+) T cells with differing function were identified. Notably, CD45RA(-)CD25(int)FOXP3(low) T cells lack suppressive function and secrete the proinflammatory cytokine IL-17. Therefore, we evaluated whether the relative fractions of CD4(+)FOXP3(+) subsets are altered in new-onset T1D subjects. We report that children with new-onset T1D have an increased proportion of CD45RA(-)CD25(int)FOXP3(low) cells that are not suppressive and secrete significantly more IL-17 than other FOXP3(+) subsets. Moreover, these T1D subjects had a higher proportion of both CD4(+) and CD8(+) T cells that secrete IL-17. The bias toward IL-17-secreting T cells in T1D suggests a role for this proinflammatory cytokine in the pathogenesis of disease.

RasGRP1 regulates antigen-induced developmental programming by naive CD8 T cells

Ag encounter by naive CD8 T cells initiates a developmental program consisting of cellular proliferation, changes in gene expression, and the formation of effector and memory T cells. The strength and duration of TCR signaling are known to be important parameters regulating the differentiation of naive CD8 T cells, although the molecular signals arbitrating these processes remain poorly defined. The Ras-guanyl nucleotide exchange factor RasGRP1 has been shown to transduce TCR-mediated signals critically required for the maturation of developing thymocytes. To elucidate the role of RasGRP1 in CD8 T cell differentiation, in vitro and in vivo experiments were performed with 2C TCR transgenic CD8 T cells lacking RasGRP1. In this study, we report that RasGRP1 regulates the threshold of T cell activation and Ag-induced expansion, at least in part, through the regulation of IL-2 production. Moreover, RasGRP1(-/-) 2C CD8 T cells exhibit an anergic phenotype in response to cognate Ag stimulation that is partially reversible upon the addition of exogenous IL-2. By contrast, the capacity of IL-2/IL-2R interactions to mediate Ras activation and CD8 T cell expansion and differentiation appears to be largely RasGRP1-independent. Collectively, our results demonstrate that RasGRP1 plays a selective role in T cell signaling, controlling the initiation and duration of CD8 T cell immune responses.

Preferential development of CD4 and CD8 T regulatory cells in RasGRP1-deficient mice

RasGRP1 and Sos are two Ras-guanyl-nucleotide exchange factors that link TCR signal transduction to Ras and MAPK activation. Recent studies demonstrate positive selection of developing thymocytes is crucially dependent on RasGRP1, whereas negative selection of autoreactive thymocytes appears to be RasGRP1 independent. However, the role of RasGRP1 in T regulatory (Treg) cell development and function is unknown. In this study, we characterized the development and function of CD4(+)CD25(+)Foxp3(+) and CD8(+)CD44(high)CD122(+) Treg lineages in RasGRP1(-/-) mice. Despite impaired CD4 Treg cell development in the thymus, the periphery of RasGRP1(-/-) mice contained significantly increased frequencies of CD4(+)Foxp3(+) Treg cells that possessed a more activated cell surface phenotype. Furthermore, on a per cell basis, CD4(+)Foxp3(+) Treg cells from mutant mice are more suppressive than their wild-type counterparts. Our data also suggest that the lymphopenic environment in the mutant mice plays a dominant role of favored peripheral development of CD4 Treg cells. These studies suggest that whereas RasGRP1 is crucial for the intrathymic development of CD4 Treg cells, it is not required for their peripheral expansion and function. By contrast to CD4(+)CD25(+)Foxp3(+) T cells, intrathymic development of CD8(+)CD44(high)CD122(+) Treg cells is unaffected by the RasGRP1(-/-) mutation. Moreover, RasGRP1(-/-) mice contained greater numbers of CD8(+)CD44(high)CD122(+) T cells in the spleen, relative to wild-type mice. Activated CD8 Treg cells from RasGRP1(-/-) mice retained their ability to synthesize IL-10 and suppress the proliferation of wild-type CD8(+)CD122(-) T cells, albeit at a much lower efficiency than wild-type CD8 Treg cells.

Chronic immunodeficiency in mice lacking RasGRP1 results in CD4 T cell immune activation and exhaustion

The Ras-guanyl nucleotide exchange factor RasGRP1 is an important link between TCR-mediated signaling and the activation of Ras and its downstream effectors. RasGRP1 is especially critical for the survival and differentiation of developing thymocytes whereas negative selection of thymocytes bearing an autoreactive TCR appears to be RasGRP1 independent. Despite apparently normal central tolerance, RasGRP1(-/-) mice spontaneously acquire an acutely activated and proliferating CD4 T cell population that exhibits characteristics of T cell exhaustion, including strong expression of programmed cell death-1. To elucidate the basis for RasGRP1(-/-) CD4 T cell immune activation, we initiated a series of adoptive transfer experiments. Remarkably, the copious amounts of cytokines and self-Ags present in hosts made lymphopenic through irradiation failed to induce the majority of RasGRP1(-/-) CD4 T cells to enter cell cycle. However, their infusion into either congenitally T cell- or T/B cell-deficient recipients resulted in robust proliferation and L-selectin down-regulation. These findings imply that the activation and proliferation of RasGRP1(-/-) CD4 T cells may be dependent on their residence in a chronically immunocompromised environment. Accordingly, bacterial and viral challenge experiments revealed that RasGRP1(-/-) mice possess a weakened immune system, exhibiting a T cell-autonomous defect in generating pathogen-specific T cells and delayed pathogen clearance. Collectively, our study suggests that chronic T cell immunodeficiency in RasGRP1(-/-) mice may be responsible for CD4 T cell activation, proliferation, and exhaustion.

Impaired T cell function and CD8 memory maintenance in a novel IL-7Rα knock-in mouse (B30)

Interleukin (IL)-7 is an essential growth factor for thymocyte development and survival of peripheral T cells, specifically CD8+ memory T cells. Current models such as IL-7 or IL-7 receptor alpha (IL-7Rα) knock-out mice have demonstrated the necessity of IL-7 signaling in these processes, but are unable to delineate the involvement of downstream pathways. To more precisely identify signals governing IL-7 function in vivo, we have disrupted the IL-7Rα Y449XXM motif in mice by knock-in mutagenesis (IL-7Rα449F). Thymocytes from these mice overcome a double negative (DN) stage developmental block that allows subsequent T cell maturation and peripheral migration. This is in stark contrast to the severe cytopenia seen in IL-7Rα−/− mice. These findings highlight the importance of IL-7Rα Y449-mediated signals during thymopoiesis, but also indicate a requirement for Y449-independent signals. Infection of IL-7Rα449F mice with the intracellular pathogen Listeria monocytogenes revealed that CD4 and CD8 T cells had different requirements for IL-7Rα signals. Strikingly, CD4 T cells failed to mount a detectable primary response to Listeria. Despite normal CD8 primary responses, maintenance of Listeria-specific CD8 memory was impaired in IL-7Rα449F mice. Furthermore, we show that Bcl-2 is IL-7Rα Y449-independent and insufficient for IL-7-mediated maintenance of CD8 memory.

Research funded by the Canadian Institutes of Health Research and the Michael Smith Foundation for Health Research

Impaired CD8 T cell memory and CD4 T cell primary responses in IL-7R alpha mutant mice

Loss of interleukin (IL)-7 or the IL-7 receptor alpha (IL-7Ralpha, CD127) results in severe immunodeficiencies in mice and humans. To more precisely identify signals governing IL-7 function in vivo, we have disrupted the IL-7Ralpha Y449XXM motif in mice by knock-in mutagenesis (IL-7Ralpha(449F)). Thymic precursors were reduced in number in IL-7Ralpha(449F) mice, but in marked contrast to IL-7Ralpha(-/-) knockout mice, thymocytes and peripheral T cells developed normally. Strikingly, Listeria infection revealed that CD4 and CD8 T cells had different requirements for IL-7Ralpha signals. CD4 T cells failed to mount a primary response, but despite normal CD8 primary responses, maintenance of CD8 memory was impaired in IL-7Ralpha(449F) mice. Furthermore, we show that Bcl-2 is IL-7Ralpha Y449 independent and insufficient for IL-7-mediated maintenance of CD8 memory.

RasGRP1 Transmits Prodifferentiation TCR Signaling That Is Crucial for CD4 T Cell Development

TCR signaling plays a governing role in both the survival and differentiation of bipotent double-positive thymocytes into the CD4(+) and CD8(+) single-positive T cell lineages. A central mediator of this developmental program is the small GTPase Ras, emitting cytoplasmic signals through downstream MAPK pathways and eventually affecting gene expression. TCR signal transduction orchestrates the activation of Ras by integrating at least two Ras-guanyl nucleotide exchange factors, RasGRP1 and Sos. In this study, we have characterized the relationship between RasGRP1 function and its potential roles in promoting ERK activity, cell survival, maturation, and lineage commitment. Investigations on RasGRP1(-/-) mice expressing a transgenic (Tg) MHC class II-restricted TCR revealed that the development of CD4 T cells expressing this Tg TCR is completely dependent on RasGRP1. Unexpectedly, a small number of functional CD8 single-positive thymocytes expressing the Tg MHC class II-restricted TCR exists in mutant mice. In addition, RasGRP1(-/-) double-positive thymocytes exhibit marked deficits in TCR-stimulated up-regulation of the positive selection marker CD69 and the antiapoptotic protein Bcl-2, whereas CD5 induction is unaffected. To evaluate the role of RasGRP1 in providing cellular survival signaling, we enforced Bcl-2 expression in RasGRP1(-/-) thymocytes. These studies demonstrate that RasGRP1 function cannot be fully complemented by Tg Bcl-2 expression. Therefore, we propose that RasGRP1 transmits differentiation signaling critically required for CD4 T cell development.

TNF Receptor Type 2 (p75) Functions as a Costimulator for Antigen-Driven T Cell Responses In Vivo

Naive T cells require costimulation for robust Ag-driven differentiation and survival. Members of the TNFR family have been shown to provide costimulatory signals conferring survival at distinct phases of the T cell response. In this study, we show that CD4 and CD8 T cells depend on TNFR type 2 (p75) for survival during clonal expansion, allowing larger accumulation of effector cells and conferring protection from apoptosis for a robust memory pool in vivo. We demonstrate using the MHC class I-restricted 2C TCR and MHC class II-restricted AND TCR transgenic systems that TNFR2 regulates the threshold for clonal expansion of CD4 and CD8 T cell subsets in response to cognate Ag. Using a novel recombinant Listeria monocytogenes (rLM) expressing a secreted form of the 2C agonist peptide (SIY) to investigate the role of TNFR2 for T cell immunity in vivo, we found that TNFR2 controls the survival and accumulation of effector cells during the primary response. TNFR2-/- CD8 T cells exhibit loss of protection from apoptosis that is correlated with diminished survivin and Bcl-2 expression. Null mutant mice were more susceptible to rLM-SIY challenge at high doses of primary infection, correlating with impaired LM-specific T cell response in the absence of TNFR2-mediated costimulation. Moreover, the resulting memory pools specific for SIY and listeriolysin O epitopes derived from rLM-SIY were diminished in TNFR2-/- mice. Thus, examination of Ag-driven T cell responses revealed a hitherto unknown costimulatory function for TNFR2 in regulating T cell survival during the differentiation program elicited by intracellular pathogen in vivo.

Self-reactive memory-phenotype CD8 T cells exhibit both MHC-restricted and non-MHC-restricted cytotoxicity: a role for the T-cell receptor and natural killer cell receptors

We have recently shown that interleukin-2 (IL-2)-activated CD8(+)CD44(hi) cells from normal mice express both adaptive and innate immune system receptors and specifically kill syngeneic tumor cells, particularly those that express NKG2D ligands. Here we show that CD8+ T cells from antigen-expressing H-Y T-cell receptor (TCR) transgenic mice also exhibit characteristics of both T cells and natural killer (NK) cells. Interaction with cognate self-antigen was required for the optimal expansion of these cells in peripheral lymphoid tissues. Although these cells possess a higher activation threshold relative to naive T cells, they can be activated by cytokine alone in vitro. They also undergo bystander proliferation in response to a bacterial infection in vivo. Interestingly, upon activation, the cells express the NKG2D receptor as well as the DNAX activation protein 12 (DAP12) adaptor protein. We provide evidence that NKG2D can act additively with the TCR in the killing of target cells, and it can also function as a directly activating receptor in non-major histocompatibility complex (MHC)-restricted killing of target cells. These properties of CD8+ T cells from H-Y TCR transgenic mice are remarkably similar to CD8(+)CD44(hi) cells that are found in normal mice. The H-Y TCR transgenic mice provide a well-defined system for characterizing the developmental biology and function of these cells.

Sialyltransferase specificity in selectin ligand formation

Selectin ligands are glycan structures that participate in leukocyte trafficking and inflammation. At least 6 ST3Gal sialyltransferases (I-VI) have been identified that may contribute to selectin ligand formation. However, it is not known which of these sialyltransferases are involved in vivo and whether they may differentially regulate selectin function. We have produced and characterized mice genetically deficient in ST3Gal-I, ST3Gal-II, ST3Gal-III, and ST3Gal-IV. Unlike mice bearing severe defects in selectin ligand formation, there was no finding of leukocytosis with these single ST3Gal deficiencies. Among neutrophils, only ST3Gal-IV was found to play a role in the synthesis of selectin ligands. In vitro rolling of marrow-derived neutrophils on E- or P-selectins presented by Chinese hamster ovary cells was reduced in the absence of ST3Gal-IV. However, in a tumor necrosis factor alpha (TNF-alpha)-induced inflammation model in vivo, no defect among P-selectin ligands was observed. Nevertheless, the number of leukocytes rolling on postcapillary venules in an E-selectin-dependent manner was decreased while E-selectin-dependent rolling velocity was increased. We propose that multiple ST3Gal sialyltransferases contribute to selectin ligand formation, as none of these ST3Gal deficiencies recapitulated the degree of E- and P-selectin ligand deficit observed on neuraminidase treatment of intact neutrophils. Our findings indicate a high degree of functional specificity among sialyltransferases and a substantial role for ST3Gal-IV in selectin ligand formation.

RasGRP1 transduces low-grade TCR signals which are critical for T cell development, homeostasis, and differentiation

Two important Ras-guanyl nucleotide exchange factors, Sos and RasGRP1, control Ras activation in thymocytes. However, the relative contribution of these two exchange factors to Ras/ERK activation and their resulting impact on positive and negative selection is unclear. We have produced two lines of RasGRP1(-/-) TCR transgenic mice to determine the effect of RasGRP1 in T cell development under conditions of defined TCR signaling. Our results demonstrate that RasGRP1 is crucial for thymocytes expressing weakly selecting TCRs whereas those that express stronger selecting TCRs are more effective at utilizing RasGRP1-independent mechanisms for ERK activation and positive selection. Analysis of RasGRP1(-/-) peripheral T cells also revealed hitherto unidentified functions of RasGRP1 in regulating T cell homeostasis and sustaining antigen-induced developmental programming.

TCR/self-antigen interactions drive double-negative T cell peripheral expansion and differentiation into suppressor cells

Mature CD4-CD8- alphabeta+ T cells (DNTC) in the periphery of TCR transgenic mice are resistant to clonal deletion in cognate Ag-expressing (Ag+) mice. Previously, we have characterized DNTC populations bearing the alloreactive 2C TCR in Ag-free (Ag-) and Ag+ mice. Despite appearing functionally anergic when challenged with cognate Ag in vitro, Ag-experienced DNTC exhibit markers of activation/memory, a lowered threshold of activation, ex vivo cytolytic activity, and the ability to rapidly secrete IFN-gamma. Remarkably, these memory-like DNTC also possess potent immunoregulatory properties, competing effectively for bystander-produced IL-2 and suppressing autoreactive CD8+ T cell proliferation via a Fas/FasL-dependent cytolytic mechanism. The fact that DNTC recovered from Ag+ mice possess markers and attributes characteristic of naive CD8+ T cells that have undergone homeostasis-induced proliferation suggested that they may be derived from a similar peripheral expansion process. Naive DNTC adoptively transferred into Ag-bearing hosts rapidly acquire markers and functional attributes of DNTC that have continually developed in the presence of Ag. Thus, the peripheral selection and maintenance of such autoreactive cells may serve to negatively regulate potential autoimmune T cell responses.

Developmentally regulated glycosylation of the CD8alphabeta coreceptor stalk modulates ligand binding

The functional consequences of glycan structural changes associated with cellular differentiation are ill defined. Herein, we investigate the role of glycan adducts to the O-glycosylated polypeptide stalk tethering the CD8alphabeta coreceptor to the thymocyte surface. We show that immature CD4(+)CD8(+) double-positive thymocytes bind MHCI tetramers more avidly than mature CD8 single-positive thymocytes, and that this differential binding is governed by developmentally programmed O-glycan modification controlled by the ST3Gal-I sialyltransferase. ST3Gal-I induction and attendant core 1 sialic acid addition to CD8beta on mature thymocytes decreases CD8alphabeta-MHCI avidity by altering CD8alphabeta domain-domain association and/or orientation. Hence, glycans on the CD8beta stalk appear to modulate the ability of the distal binding surface of the dimeric CD8 globular head domains to clamp MHCI.

p59fyn (Fyn) promotes the survival of anergic CD4-CD8- alpha beta TCR+ cells but negatively regulates their proliferative response to antigen stimulation

T cell anergy is characterized by alterations in TCR signaling that may play a role in controlling the unresponsiveness of the anergic cell. We have addressed questions regarding the importance of the Src kinase p59(fyn) (Fyn) in this process by using Fyn null mice. We demonstrate that a mature population of CD4(-)CD8(-) alphabeta TCR(+) anergic T cells lacking Fyn have a substantial recovery of their proliferation defect in response to Ag stimulation. This recovery cannot be explained by ameliorated production of IL-2, and the improved proliferation correlates with an enhanced ability of the Fyn(-/-) anergic T cells to up-regulate the high affinity IL-2 receptor. We also observe that anergic CD4(-)CD8(-) alphabeta TCR(+) T cells have a heightened survival ability that is partially dependent on the elevated levels of Fyn and IL-2 receptor beta-chain expressed by these cells. The enhanced survival correlates with an increased capacity of the anergic cells to respond to IL-15. We conclude that Fyn plays an important role in aspects of T cell anergy pertaining to TCR signaling and to cell survival.

The ST3Gal-I sialyltransferase controls CD8+ T lymphocyte homeostasis by modulating O-glycan biosynthesis

T lymphocyte activation evokes distinct changes in cell surface O-glycans. CD8+ T cells undergo an elimination of sialic acid on core 1 O-glycans and an induction of core 2 O-glycans until either apoptotic death or differentiation into memory cells. We find that the ST3Gal-I sialyltransferase is required for core 1 O-glycan sialylation and its deficiency induces core 2 O-glycan biosynthesis. Apoptosis ensues with the loss of peripheral CD8+ T cells in the absence of immune stimulation. Cell surface ligation of the ST3Gal-I substrate CD43 recapitulates this phenotype by a caspase 3-independent mechanism. Control of core 1 O-glycan sialylation in T lymphocytes by ST3Gal-I comprises a homeostatic mechanism that eliminates CD8+ T cells by apoptosis while facilitating the production of viable CD8+ memory T cells.

Isolation, characterization and inactivation of the mouse Mgat3 gene: the bisecting N-acetylglucosamine in asparagine-linked oligosaccharides appears dispensable for viability and reproduction

The biosynthesis of complex asparagine (N)-linked oligosaccharides in vertebrates proceeds with the linkage of N-acetylglucosamine (GlcNAc) to the core mannose residues. UDP-N-acetylglucosamine:beta-D-mannoside beta 1-4 N-acetylglucosaminyltransferase III (GlcNAc-TIII, EC2.4.1.144) catalyzes the addition of GlcNAc to the mannose that is itself beta 1-4 linked to underlying N-acetylglucosamine. GlcNAc-TIII thereby produces what is known as a 'bisecting' GlcNAc linkage which is found on various hybrid and complex N-glycans. GlcNAc-TIII can also play a regulatory role in N-glycan biosynthesis as addition of the bisecting GlcNAc eliminates the potential for alpha-mannosidase-II, GlcNAc-TII, GlcNAc-TIV, GlcNAc-TV, and core alpha 1-6-fucosyltransferase to act subsequently. To investigate the physiologic relevance of GlcNAc-TIII function and bisected N-glycans, the mouse gene encoding GlcNAc-TIII (Mgat3) was cloned, characterized, and inactivated using Cre/loxP site-directed recombination. The Mgat3 gene is highly conserved in comparison to the rat and human homologs and is normally expressed at high levels in mammalian brain and kidney tissues. Using fluorescence in situ hybridization (FISH), the Mgat3 gene was regionally mapped to chromosome 15E11, near the Scn8a sodium channel gene at 15F1. Following homologous recombination in embryonic stem cells and Cre mediated gene deletion, Mgat3-deficient mice were produced that lacked GlcNAc-TIII activity and were deficient in E4-PHA visualized GlcNAc-bisected N-linked oligosaccharides. Nevertheless, GlcNAc-TIII deficient mice were found to be viable and reproduced normally. Moreover, such mice exhibited normal cellularity and morphology among organs including brain and kidney. No alterations were apparent in circulating leukocytes, erythrocytes or in serum metabolite levels that reflect kidney function. We thus find that GlcNAc-TIII and the bisecting GlcNAc in N-glycans appear dispensable for normal development, homeostasis and reproduction in the mouse.