Cell-mediated Immune Diseases Research Articles

Understanding New Regulatory Mechanism of TCR Signal Transduction

Signal-transducing adaptor protein-2 (STAP-2) is a unique scaffold protein that regulates several immunological signaling pathways, including LIF/LIF receptor and LPS/TLR4 signals. STAP-2 is required for Fas/FasL-dependent T cell apoptosis and SDF-1α-induced T cell migration. Conversely, STAP-2 modulates integrin-mediated T cell adhesion, suggesting that STAP-2 is essential for several negative and positive T cell functions. However, whether STAP-2 is involved in T cell-antigen receptor (TCR)-mediated T cell activation is unknown. STAP-2 deficiency was recently reported to suppress TCR-mediated T cell activation by inhibiting LCK-mediated CD3ζ and ZAP-70 activation. Using STAP-2 deficient mice, it was demonstrated that STAP-2 is required for the pathogenesis of Propionibacterium acnes-induced granuloma formation and experimental autoimmune encephalomyelitis. Here, detailed functions of STAP-2 in TCR-mediated T cell activation, and how STAP-2 affects the pathogenesis of T cell-mediated inflammation and immune diseases, are reviewed.

Immunomodulatory Mechanism and Potential Application of Dental Pulp-Derived Stem Cells in Immune-Mediated Diseases.

Dental pulp stem cells (DPSCs) are mesenchymal stem cells (MSCs) derived from dental pulp tissue, which have high self-renewal ability and multi-lineage differentiation potential. With the discovery of the immunoregulatory ability of stem cells, DPSCs have attracted much attention because they have similar or even better immunomodulatory effects than MSCs from other sources. DPSCs and their exosomes can exert an immunomodulatory ability by acting on target immune cells to regulate cytokines. DPSCs can also migrate to the lesion site to differentiate into target cells to repair the injured tissue, and play an important role in tissue regeneration. The aim of this review is to summarize the molecular mechanism and target cells of the immunomodulatory effects of DPSCs, and the latest advances in preclinical research in the treatment of various immune-mediated diseases, providing new reflections for their clinical application. DPSCs may be a promising source of stem cells for the treatment of immune-mediated diseases.

Eomesodermin-expressing type 1 regulatory (EOMES+ Tr1)-like T cells: Basic biology and role in immune-mediated diseases.

Type 1 regulatory (Tr1) T cells are currently defined all T cells with regulatory functions that lack FOXP3 expression and produce IL-10. Tr1 cells are heterogeneous, and the different reported properties of Tr1-cell populations have caused some confusion in the field. Moreover, understanding the role of Tr1 cells in immune-mediated diseases has been hampered by the lack of a lineage-defining transcription factor. Several independent studies indicated recently that the transcription factor Eomesodermin (EOMES) could act as a lineage-defining transcription factor in a population of IL-10 and IFN-γ co-producing Tr1-like cells, since EOMES directly induces IFN-γ and cytotoxicity, enhances IL-10, and antagonizes alternative T-cell fates. Here, we review the known properties of EOMES+ Tr1-like cells. They share several key characteristics with other Tr1 cells (i.e., "Tr1-like"), namely high IL-10 production, cytotoxicity, and suppressive capabilities. Notably, they also share some features with FOXP3+ Tregs, like downregulation of IL-7R and CD40L. In addition, they possess several unique, EOMES-dependent features, that is, expression of GzmK and IFN-γ, and downregulation of type-17 cytokines. Published evidence indicates that EOMES+ Tr1-like cells play key roles in graft-versus-host disease, colitis, systemic autoimmunity and in tumors. Thus, EOMES+ Tr1-like cells are key players of the adaptive immune system that are involved in several different immune-mediated diseases.

The Functional Properties and Physiological Roles of Signal-Transducing Adaptor Protein-2 in the Pathogenesis of Inflammatory and Immune Disorders.

Adaptor molecules play a crucial role in signal transduction in immune cells. Several adaptor molecules, such as the linker for the activation of T cells (LAT) and SH2 domain-containing leukocyte protein of 76 kDa (SLP-76), are essential for T cell development and activation following T cell receptor (TCR) aggregation, suggesting that adaptor molecules are good therapeutic targets for T cell-mediated immune disorders, such as autoimmune diseases and allergies. Signal-transducing adaptor protein (STAP)-2 is a member of the STAP family of adaptor proteins. STAP-2 functions as a scaffold for various intracellular proteins, including BRK, signal transducer, and activator of transcription (STAT)3, STAT5, and myeloid differentiation primary response protein (MyD88). In T cells, STAP-2 is involved in stromal cell-derived factor (SDF)-1α-induced migration, integrin-dependent cell adhesion, and Fas-mediated apoptosis. We previously reported the critical function of STAP-2 in TCR-mediated T cell activation and T cell-mediated autoimmune diseases. Here, we review how STAP-2 affects the pathogenesis of T cell-mediated inflammation and immune diseases in order to develop novel STAP-2-targeting therapeutic strategies.

Follicular regulatory T cell biology and its role in immune-mediated diseases.

Follicular regulatory T (Tfr) cells are recently found to be a special subgroup of regulatory T (Treg) cells. Tfr cells play an important role in regulating the germinal center (GC) response, especially modulating follicular helper T (Tfh) cells and GC-B cells, thereby affecting the production of antibodies. Tfr cells are involved in the generation and development of many immune-related and inflammatory diseases. This article summarizes the advances in several aspects of Tfr cell biology, with special focus on definition and phenotype, development and differentiation, regulatory factors, functions, and interactions with T/B cells and molecules involved in performance and regulation of Tfr function. Finally, we highlight the current understanding of Tfr cells involvement in autoimmunity and alloreactivity, and describe some drugs targeting Tfr cells. These latest studies have answered some basic questions in Tfr cell biology and explored the roles of Tfr cells in immune-mediated diseases.

Treg cell therapy: How cell heterogeneity can make the difference.

CD4+ CD25high CD127low/- FOXP3+ T regulatory cells are responsible for maintaining immune tolerance and controlling excessive immune responses. Treg cell use in pre-clinical animal models showed the huge therapeutic potential of these cells in immune-mediated diseases and laid the foundations for their applications in therapy in humans. Currently, there are several clinical trials utilizing the adoptive transfer of Treg cells to reduce the morbidity in autoimmune disorders, allogeneic HSC transplantation, and solid organ transplantation. However, a large part of them utilizes total Treg cells without distinction of their biological variability. Many studies on the heterogeneity of Treg cell population revealed distinct subsets with different functions in the control of the immune response and induction of peripheral tolerance. Some of these subsets also showed a role in controlling the general homeostasis of non-lymphoid tissues. All these Treg cell subsets and their peculiar properties can be therefore exploited to develop novel therapeutic approaches. This review describes these functionally distinct subsets, their phenotype, homing properties and functions in lymphoid and non-lymphoid tissues. In addition, we also discuss the limitations in using Treg cells as a cellular therapy and the strategies to enhance their efficacy.

HLA-G Expressing Immune Cells in Immune Mediated Diseases.

HLA-G is a HLA class Ib antigen that possesses immunomodulatory properties. HLA-G-expressing CD4+ and CD8+ T lymphocytes, NK cells, monocytes, and dendritic cells with immunoregulatory functions are present in small percentages of patients with physiologic conditions. Quantitative and qualitative derangements of HLA-G+ immune cells have been detected in several conditions in which the immune system plays an important role, such as infectious, neoplastic, and autoimmune diseases as well as in complications from transplants and pregnancy. These observations strongly support the hypothesis that HLA-G+ immune cells may be implicated in the complex mechanisms underlying the pathogenesis of these disorders.

Engineered Type-1 Regulatory T Cells as Cellular Therapy for Treatment of Immune Mediated Diseases

Abstract Type 1 regulatory cells (Tr1) are a promising cellular product for suppression of effector T cells in immune mediated diseases, including graft-versus-host-disease (GvHD) in allogeneic hematopoietic stem cell transplantation (allo-HSCT) (Roncarolo et al. Immunity 2018). We have developed an in vitro protocol to produce Tr1 cells by lentiviral transduction of the human IL10 with a constitutive promoter into human CD4+ T cells (Locafaro et al. Molecular Therapy 2017). These engineered Tr1 cells, called LV-10, acquire a characteristic Tr1 cytokine profile (IL-10 and IFN-g high, IL-4 low and expression of intracellular perforin and granzyme B). In vitro, LV-10 cells suppress the proliferation of responder CD4+ T cells upon activation by allogeneic dendritic cells. LV-10 cells also degranulate in response to and kill myeloid cells, including myeloid blasts from patients with acute myeloid leukemia, through a granzyme B- and perforin-dependent mechanism. Interestingly, the ability to degranulate and kill myeloid cells is not present when LV-10 are activated and expanded with anti-CD3 and anti-CD28 coated beads, suggesting that signals beyond TCR, CD28, and IL-10 receptor pathway activation are necessary to reprogram LV-10 cells into cytotoxic cells. In vivo, LV-10 cells injected into NSG mice do not induce xeno-GvHD, in contrast to control CD4+ T cells. In addition, LV-10 cells suppress CD4-induced xeno-GvHD and prevent expansion of myeloid leukemic cells. Experiments are ongoing to compare the potency and in vivo survival of allogeneic vs autologous LV-10 cells. These findings demonstrate the promise of using LV-10 to treat immune mediated diseases, including GvHD in AML patients receiving allo-HSCT.

SOCS1 Regulates the Immunomodulatory Roles of MSCs on B Cells.

Background and ObjectivesThe effective use of MSCs for the treatment of some B cell-mediated immune diseases is quite limited. The main reason is that the immunomodulatory effects of mesenchymal stem cells (MSCs) on B cells are unclear, and their underlying mechanisms have not been fully explored.Methods and ResultsBy co-culturing B cells with MSCs without (MSC/CTLsh) or with suppressor of cytokine signaling 1 (SOCS1) knockdown (MSC/SOCS1sh), we found that MSCs inhibited B cell proliferation, activation and terminal differentiation. Remarkably, the highest inhibition of B cell proliferation was observed in MSC/SOCS1sh co-culture. Besides, MSC/SOCS1sh reversed the inhibitory effect of MSCs in the last stage of B cell differentiation. However, MSC/SOCS1sh had no effect on inhibiting B cell activation by MSCs. We also showed that IgA+ B cell production was significantly higher in MSC/SOCS1sh than in MSC/CTLsh, although no difference was observed when both MSCs co-cultures were compared to isolated B cells. In addition, MSCs increased PGE2 production after TNF-α/IFN-γ stimulation, with the highest increase observed in MSC/SOCS1sh co-culture.ConclusionsOur results highlighted the role of SOCS1 as an important new mediator in the regulation of B cell function by MSCs. Therefore, these data may help to develop new treatments for B cell-mediated immune diseases.

Involvement of Yin Yang 1 (YY1) Expression in T-Cell Subsets Differentiation and Their Functions: Implications in T Cell-Mediated Diseases.

The transcription factor Yin Yang 1 (YY1) has been implicated in embryogenesis, cell differentiation, organ development, and regulation of T cell-mediated immune diseases. YY1 has been reported to act as an activator or repressor, or both, of various genes depending on the nature of the tissue and their context. Although the roles of YY1 in both pathogenesis and progression of tumors has been the subject of many reports, the roles of YY1 in the immune system are not as well known. In this review, we examine the literature on the role of YY1 in both the differentiation and the development of various subsets of the T lymphocytes and examined its molecular role in these areas. We examined the role of YY1 in the thymus for the development of both CD4 and CD8 T lymphocytes, the various CD4 subsets, Th1, Th2, Th17, and Treg. Our analyses revealed that the presence of YY1 is necessary for maturation and proliferation of the αβ lineage through its role in mediating the apoptotic pathway. Moreover, in differentiation of T cell subsets, YY1 controls the expression of the Th2 master regulator GATA3, the Treg inducer Foxp3, as well as IL-12 expression, which is important in regulating production of Th1 cytokines. Furthermore, the role of YY1 in the Th17 signaling pathway has not been fully identified, although recent studies have suggested that differentiation of Th17 involves synergistic action of YY1 and STAT3. The previously mentioned findings strongly suggest that the role of YY1 in T cells is critical in both their normal differentiation and the induction of T cell-mediated autoimmune diseases. Clearly, such findings suggest the potential therapeutic applications of YY1 inhibitors to alleviate its role in autoimmune diseases.

Histone deacetylase function in CD4+ T cells.

The differentiation of T helper cell subsets and their acquisition of effector functions are accompanied by changes in gene expression programmes, which in part are regulated and maintained by epigenetic processes. Histone deacetylases (HDACs) and histone acetyltransferases (HATs) are key epigenetic regulators that function by mediating dynamic changes in the acetylation of histones at lysine residues. In addition, many non-histone proteins are also acetylated, and reversible acetylation affects their functional properties, demonstrating that HDACs mediate effects beyond the epigenetic regulation of gene expression. In this Review, we discuss studies revealing that HDACs are key regulators of CD4+ T cell-mediated immunity in mice and humans and that HDACs are promising targets in T cell-mediated immune diseases. Finally, we discuss unanswered questions and future research directions to promote the concept that isoform-selective HDAC inhibitors might broaden the clinical application of HDAC inhibitors beyond their current use in certain types of cancer.

Guanine and inosine nucleotides/nucleosides suppress murine T cell activation

Damaged tissues and cells release intracellular purine nucleotides, which serve as intercellular signaling factors. We previously showed that exogenously added adenine nucleotide (250 μM ATP) suppressed the activation of murine splenic T lymphocytes. Here, we examined the effects of other purine nucleotides/nucleosides on mouse T cell activation. First, we found that pretreatment of mouse spleen T cells with 250 μM GTP, GDP, GMP, guanosine, ITP, IDP, IMP or inosine significantly reduced the release of stimulus-inducible cytokine IL-2. This suppression of IL-2 release was not caused by induction of cell death. Further studies with GTP, ITP, guanosine and inosine showed that pretreatment with these nucleotides/nucleosides also suppressed release of IL-6. However, these nucleotides/nucleosides did not suppress stimulus-induced phosphorylation of ERK1/2, suggesting that the suppression of the release of inflammatory cytokines does not involve inhibition of ERK1/2 signaling. In contrast to ATP pretreatment at the same concentration, guanine or inosine nucleotides/nucleosides did not attenuate the expression of CD25. Our findings indicate that exogenous guanine or inosine nucleotides/nucleosides can suppress inflammatory cytokine release from T cells, and may be promising candidates for use as supplementary agents in the treatment of T cell-mediated immune diseases.

Adenine Nucleotides Attenuate Murine T Cell Activation Induced by Concanavalin A or T Cell Receptor Stimulation.

Extracellular ATP and its metabolites affect various cellular immune responses, including T cell function, but there are apparently conflicting reports concerning the effects of adenine nucleotides on T cells. For example, it has been reported that ATP-mediated activation of P2 receptor is involved in T cell activation; activation of adenosine receptors suppresses T cell function; and 1 mM ATP induces T cell death via activation of P2X7 receptor. Therefore, in this work we investigated in detail the effects of 100–250 μM ATP, ADP, or AMP on murine T cell activation. First, an in vitro study showed that pretreatment of murine splenic T cells with 100–250 μM ATP, ADP, or AMP significantly suppressed the concanavalin A (ConA)-induced release of cytokines, including IL-2. This suppression was not due to induction of cell death via the P2X7 receptor or to an immunosuppressive effect of adenosine. ATP attenuated the expression of CD25, and decreased the cell proliferation ability of activated T cells. The release of IL-2 by ConA-stimulated lymphocytes was suppressed by post-treatment with ATP, as well as by pretreatment. These results suggest that exogenous ATP suppresses the activation of T cells. Secondly, we evaluated the effect of ATP in a ConA-treated mice. Treatment with ATP attenuated the increase of IL-2 concentration in the blood. Overall, these results suggest that adenine nucleotides might have potential as supplemental therapeutic agents for T cell-mediated immune diseases, by suppressing T cell activation.

PKM2 Is Required to Activate Myeloid Dendritic Cells from Patients with Severe Aplastic Anemia.

Severe aplastic anemia (SAA) is an autoimmune disease in which bone marrow failure is mediated by activated myeloid dendritic cells (mDCs) and T lymphocytes. Recent research has identified a strong immunomodulatory effect of pyruvate kinase M2 (PKM2) on dendritic cells in immune-mediated diseases. In this study, we aimed to explore the role of PKM2 in the activation of mDCs in SAA. We observed conspicuously higher levels of PKM2 in mDCs from SAA patients compared to normal controls at both the gene and protein levels. Concurrently, we unexpectedly discovered that after the mDC-specific downregulation of PKM2, mDCs from patients with SAA exhibited weakened phagocytic activity and significantly decreased and shortened dendrites relative to their counterparts from normal controls. The expression levels of the costimulatory molecules CD86 and CD80 were also reduced on mDCs. Our results also suggested that PKM2 knockdown in mDCs reduced the abilities of these cells to promote the activation of CD8+ T cells (CTLs), leading to the decreased secretion of cytotoxic factors by the latter cell type. These findings demonstrate that mDC activation requires an elevated intrinsic PKM2 level and that PKM2 improves the immune status of patients with SAA by enhancing the functions of mDCs and, consequently, CTLs.

Costunolide, a sesquiterpene lactone, inhibits the differentiation of pro-inflammatory CD4+ T cells through the modulation of mitogen-activated protein kinases

CD4+ T cell activation and adequate differentiation into effector T helper (Th) cells are crucial for mediating adaptive immune responses to cope with foreign pathogens. Despite the significant role of Th cells, excessive increases in their numbers result in inflammatory and autoimmune diseases. In this study, we investigated the effects of costunolide, a plant-derived natural compound with an anti-inflammatory activity, in regulating Th cells and the underlying mechanisms. Costunolide significantly decreased cell populations of differentiated Th1, Th2, and Th17 subsets under Th subset-polarizing conditions, while exerting statistically negligible effects on Treg cell differentiation. Furthermore, costunolide inhibited the expression level of Th subset-polarizing master genes such as T-bet, GATA3, and RORγt, indicating that costunolide inhibits the differentiation of CD4+ T cells into Th subsets. Additionally, costunolide suppressed the proliferative activity of CD4+ T cells and the expression of CD69 activation marker on CD4+ T cells. When the molecular targets of costunolide were investigated, phosphorylation of ERK and p38 was found to be decreased under Th subset-polarizing conditions, whereas activity of JNK remained unchanged. U0126, an ERK inhibitor, and SB203580, a p38 inhibitor, decreased the expression of CD69 upon TCR stimulation and inhibited CD4+ T cell differentiation, indicating that both ERK and p38 are suggested to be critical molecular targets of costunolide. Taken together, these results suggest that costunolide inhibits the differentiation of CD4+ T cells by suppressing ERK and p38 activities and can be an effective therapeutic agent for T cell-mediated immune diseases.

Immune regulation of multiple sclerosis by CD8+ T cells.

The role of CD8+ T cells in the process of autoimmune pathology has been both understudied and controversial. Multiple sclerosis (MS) is an inflammatory, demyelinating disorder of the central nervous system (CNS) with underlying T cell-mediated immunopathology. CD8+ T cells are the predominant T cells in human MS lesions, showing oligoclonal expansion at the site of pathology. It is still unclear whether these cells represent pathogenic immune responses or disease-regulating elements. Through studies in human MS and its animal model, experimental autoimmune encephalomyelitis (EAE), we have discovered two novel CD8+ T cell populations that play an essential immunoregulatory role in disease: (1) MHC class Ia-restricted neuroantigen-specific "autoregulatory" CD8+ T cells and (2) glatiramer acetate (GA/Copaxone(®)) therapy-induced Qa-1/HLA-E-restricted GA-specific CD8+ T cells. These CD8+ Tregs suppress proliferation of pathogenic CD4+ CD25- T cells when stimulated by their cognate antigens. Similarly, CD8+ Tregs significantly suppress EAE when transferred either pre-disease induction or during peak disease. The mechanism of disease inhibition depends, at least in part, on an antigen-specific, contact-dependent process and works through modulation of CD4+ T cell responses as well as antigen-presenting cells through a combination of cytotoxicity and cytokine-mediated modulation. This review provides an overview of our understanding of CD8+ T cells in immune-mediated disease, focusing particularly on our findings regarding regulatory CD8+ T cells both in MS and in EAE. Clinical relevance of these novel CD8-regulatory populations is discussed, providing insights into a potentially intriguing, novel therapeutic strategy for these diseases.

Th17 and Interleukin 23 in the Pathogenesis of Psoriatic Arthritis and Spondyloarthritis

Psoriatic arthritis and spondyloarthritis (SpA) are complex immune-mediated diseases affecting peripheral and axial joints. T cells have been considered fundamental in triggering the disease and maintaining the process in the chronic phase. The recent discovery of the CD4+ Th17 lymphocyte subset and the interleukin 23/interleukin 17 axis has further contributed to the definition of unknown pathways, challenging previous models and the role of Th1/Th2 T cells in immune mediated diseases, including SpA.

N-(4-18F-Fluorobenzoyl)Interleukin-2 for PET of Human-Activated T Lymphocytes

Interleukin-2 (IL2) binds with high affinity to the IL2 receptors overexpressed on activated T lymphocytes in various pathologic conditions. Radiolabeling of IL2 with a positron-emitting isotope could provide a tool for noninvasive PET of activated T cells in immune-mediated diseases. We report the labeling of IL2 with N-succinimidyl 4-(18)F-fluorobenzoate ((18)F-SFB) for the synthesis of N-(4-(18)F-fluorobenzoyl)interleukin-2 ((18)F-FB-IL2) and the in vitro and in vivo evaluation of this novel radiopharmaceutical for the detection of IL2 receptor-positive cells by PET. (18)F-SFB was efficiently prepared using a 3-step radiochemical pathway. Purified (18)F-SFB was incubated with IL2 in borate buffer (pH 8.5) and ethanol at 50°C for 10 min. (18)F-FB-IL2 was purified by reversed-phase high-performance liquid chromatography. As in vitro quality controls, a biologic binding assay, sodium dodecyl sulfate polyacrylamide gel electrophoresis, mass spectrometry, and 3-chloroacetic acid precipitation stability tests were performed. Biodistribution studies were performed in BALB/c mice to evaluate the distribution of the tracer in healthy animals. PET experiments were performed in severe combined immunodeficiency disease mice inoculated with phytohemoagglutinin-activated human peripheral blood mononuclear cells (hPBMc). Whole-body images were acquired 30 min after injection of 5-15 MBq of (18)F-FB-IL2. (18)F-SFB was produced with a 34%-38% radiochemical yield. The radiochemical purity after solid-phase extraction purification ranged from 93% to 96%. Conjugation of (18)F-SFB to IL2 yielded (18)F-FB-IL2 as the major product. The radiochemical yield of (18)F-FB-IL2 after high-performance liquid chromatography purification was 25%-35% based on (18)F-SFB. (18)F-FB-IL2 was stable in plasma at 37°C and capable of stimulating T cells to an extent similar to native IL2. A biodistribution study showed highest tracer uptake in the kidneys and bladder due to rapid renal clearance of the tracer. Small-animal PET images showed binding of (18)F-FB-IL2 to activated hPBMc proportional to the number of injected cells. We report the successful labeling of IL2 with (18)F for PET of activated T lymphocytes. (18)F-FB-IL2 is stable, is biologically active, and allows in vivo detection of activated T lymphocytes.

Emerging roles of prostanoids in T cell‐mediated immunity

Three distinct subsets of T helper (Th) cells, Th1, Th2, and Th17, not only contribute to host defense against pathogens, but also cause many types of immune diseases. Differentiation and functions of these T cell subsets are mainly regulated by specific cytokines. Intriguingly, recent studies have revealed that prostanoids including various types of prostaglandins (PGs) and thromboxane (TX) are also involved in these processes. Prostanoids exert their actions by binding to their specific receptors. They include PGD receptor, EP1, EP2, EP3, and EP4 subtypes of PGE receptor, PGF receptor, PGI receptor, and TX receptor. From many in vitro findings, prostanoids, especially PGE(2), were traditionally believed to be an immunosuppressant. However, studies using mice deficient in each type or subtype of prostanoid receptors and their selective agonists and antagonists have revealed that prostanoids collaborate with cytokines, and critically regulate T cell proliferation, differentiation and functions. Recent studies have revealed that PGE(2) facilitates Th1 cell differentiation and Th17 cell expansion in collaboration with IL-12 and IL-23, respectively, and that these PGE(2) actions contribute to development of immune diseases mediated by these Th subsets. Furthermore, studies using the receptor-deficient mice have also revealed that other prostanoids including PGD(2) and PGI(2) contribute to regulation of immune diseases of the Th2 type such as allergic asthma. These findings shed a new light on the roles of prostanoids in T cell-mediated immunity and immune diseases.

A functional motif QLYxxYP is essential for osteopontin induced T lymphocyte activation and migration

Osteopontin (OPN) plays an important role in regulating lymphocyte adhesion and cytokine production associated with inflammatory processes and autoimmune diseases. Here we developed and characterized a monoclonal antibody F8E11 specific for human OPN (hOPN). F8E11 could inhibit OPN-induced lymphocyte activation and migration. Epitope mapping showed that F8E11 could specifically recognize the peptide QLYxxYP. In addition, a synthesized mimetic peptide F8P (EEKQLYNKYPDA) could block the binding of F8E11 to hOPN and significantly inhibit the hOPN-induced lymphocyte migration. Moreover, mutations on the QLYxxYP motif of hOPN also markedly diminished its activity for lymphocyte activation and migration. The functioning assay indicated that this novel epitope is critically involved in the lymphocyte migration through activating MAPK/ERK/AP-1 pathway, which can be inhibited by the motif QLYxxYP blocking antibody, F8E11. These results suggest that this novel epitope of OPN may provide a potential therapeutic target for the treatment of T cell mediated-immune diseases.