Elevation of activated gamma delta T cell receptor bearing T lymphocytes in patients with autoimmune chronic liver disease

Autoimmune Hepatitis: Pathophysiology

Genome-wide association analyses suggest that HLA genes including HLA-DRB*0301, HLA-DRB*0401, and HLA-B*3501 as well as non-HLA genes including CD28/CTLA4/ICOS and SYNPR increased AIH susceptibility. The destruction of hepatocytes is the result of the imbalance between proinflammatory cells and immunosuppressive cells, especially the imbalance between Tregs and Th17 cells. The microbiome in patients with AIH is decreased in diversity with a specific decline in Bifidobacterium and enrichment in Veillonella and Faecalibacterium. Recent evidence has demonstrated the pathogenic role of E. gallinarum and L.reuteri in inducing autoimmunity in the liver.

HERV1-env Induces Unfolded Protein Response Activation in Autoimmune Liver Disease: A Potential Mechanism for Regulatory T Cell Dysfunction

Regulatory T cells (Tregs) are not terminally differentiated but can acquire effector properties. Here we report an increased expression of human endogenous retrovirus 1 (HERV1-env) proteins in Tregs of patients with de novo autoimmune hepatitis and autoimmune hepatitis, which induces endoplasmic reticulum (ER) stress. HERV1-env-triggered ER stress activates all three branches (IRE1, ATF6, and PERK) of the unfolded protein response (UPR). Our coimmunoprecipitation studies show an interaction between HERV1-env proteins and the ATF6 branch of the UPR. The activated form of ATF6α activates the expression of RORC and STAT3 by binding to promoter sequences and induces IL-17A production. Silencing of HERV1-env results in recovery of Treg suppressive function. These findings identify ER stress and UPR activation as key factors driving Treg plasticity (species: human).

Pathogenesis of Autoimmune Hepatitis-Cellular and Molecular Mechanisms

Pediatric autoimmune liver disorders include autoimmune hepatitis (AIH), autoimmune sclerosing cholangitis (ASC), and de novo AIH after liver transplantation. AIH is an idiopathic disease characterized by immune-mediated hepatocyte injury associated with the destruction of liver cells, causing inflammation, liver failure, and fibrosis, typically associated with autoantibodies. The etiology of AIH is not entirely unraveled, but evidence supports an intricate interaction among genetic variants, environmental factors, and epigenetic modifications. The pathogenesis of AIH comprises the interaction between specific genetic traits and molecular mimicry for disease development, impaired immunoregulatory mechanisms, including CD4+ T cell population and Treg cells, alongside other contributory roles played by CD8+ cytotoxicity and autoantibody production by B cells. These findings delineate an intricate pathway that includes gene to gene and gene to environment interactions with various drugs, viral infections, and the complex microbiome. Epigenetics emphasizes gene expression through hereditary and reversible modifications of the chromatin architecture without interfering with the DNA sequence. These alterations comprise DNA methylation, histone transformations, and non-coding small (miRNA) and long (lncRNA) RNA transcriptions. The current first-line therapy comprises prednisolone plus azathioprine to induce clinical and biochemical remission. Further understanding of the cellular and molecular mechanisms encountered in AIH may depict their impact on clinical aspects, detect biomarkers, and guide toward novel, effective, and better-targeted therapies with fewer side effects.

Immunobiology and immunotherapy of HCC: spotlight on innate and innate-like immune cells

Immune-based therapies such as immune checkpoint inhibitors have revolutionized the systemic treatment of various cancer types. The therapeutic application of monoclonal antibodies targeting inhibitory pathways such as programmed cell death-1(PD-1)/programmed cell death ligand 1 (PD-L1) and CTLA-4 to cells of the adaptive immune system has recently been shown to generate meaningful improvement in the clinical outcome of hepatocellular carcinoma (HCC). Nevertheless, current immunotherapeutic approaches induce durable responses in only a subset of HCC patients. Since immunologic mechanisms such as chronic inflammation due to chronic viral hepatitis or alcoholic and nonalcoholic fatty liver disease play a crucial role in the initiation, development, and progression of HCC, it is important to understand the underlying mechanisms shaping the unique tumor microenvironment of liver cancer. The liver is an immunologic organ with large populations of innate and innate-like immune cells and is exposed to bacterial, viral, and fungal antigens through the gut-liver axis. Here, we summarize and highlight the role of these cells in liver cancer and propose strategies to therapeutically target them. We also discuss current immunotherapeutic strategies in HCC and outline recent advances in our understanding of how the therapeutic potential of these agents might be enhanced.

Micronutrients in autoimmune diseases: possible therapeutic benefits of zinc and vitamin D

A functional immune system is essential for healthy life. This is achieved by the coordinate activation and interaction of different immune cells. One should be aware that activation of the immune response is as important as its deactivation when the pathogens are cleared, as otherwise host tissue can be damaged up to life-threatening levels. Autoimmune diseases (AID) represent a phenomenon of immune cells attacking host cells and tissue. Five to eight percent of the world's population are currently affected by 80-100 AID. In recent years, the incidence has been constantly increasing, reaching alarmingly high numbers particularly for type 1 diabetes mellitus, Crohn's disease, rheumatoid arthritis, Sjogren's syndrome and multiple sclerosis. This indicates a higher societal burden of AID for the future. This article provides an overview of general concepts of triggers and underlying mechanisms leading to self-destruction. Lately, several original concepts of disease etiology were revised, and there is a variety of hypotheses on triggers, underlying mechanisms and preventive actions. This article concentrates on the importance of nutrition, especially zinc and vitamin D, for balancing the immune function. Homespun nutritional remedies seem to reenter today's therapeutic strategies. Current treatment approaches are largely symptomatic or suppress the immune system. However, recent studies reveal significant benefits of nutrition-related therapeutic approaches including prevention and treatment of established disease, which offer a cost-efficient and trigger-unspecific alternative addressing balancing rather than suppression of the immune system. Zinc and vitamin D are currently the best studied and most promising candidates for therapeutic intervention.

Cellular and Molecular Mechanisms of Autoimmune Hepatitis

Autoimmune hepatitis is an uncommon idiopathic syndrome of immune-mediated destruction of hepatocytes, typically associated with autoantibodies. The disease etiology is incompletely understood but includes a clear association with human leukocyte antigen (HLA) variants and other non-HLA gene variants, female sex, and the environment. Pathologically, there is a CD4+ T cell-rich lymphocytic inflammatory infiltrate with variable hepatocyte necrosis and subsequent hepatic fibrosis. Attempts to understand pathogenesis are informed by several monogenetic syndromes that may include autoimmune liver injury, by several drug and environmental agents that have been identified as triggers in a minority of cases, by human studies that point toward a central role for CD4+ effector and regulatory T cells, and by animal models of the disease. Nonspecific immunosuppression is the current standard therapy. Further understanding of the disease's cellular and molecular mechanisms may assist in the design of better-targeted therapies, aid the limitation of adverse effects from therapy, and inform individualized risk assessment and prognostication.

Autoimmune hepatitis

Autoimmune hepatitis (AIH) is a severe liver disease that affects children and adults worldwide. The diagnosis of AIH relies on increased serum transaminase and immunoglobulin G levels, presence of autoantibodies and interface hepatitis on liver histology. AIH arises in genetically predisposed individuals when a trigger, such as exposure to a virus, leads to a T cell-mediated autoimmune response directed against liver autoantigens; this immune response is permitted by inadequate regulatory immune control leading to a loss of tolerance. AIH responds favourably to immunosuppressive treatment, which should be started as soon as the diagnosis is made. Standard regimens include fairly high initial doses of corticosteroids (prednisone or prednisolone), which are tapered gradually as azathioprine is introduced. For those patients who do not respond to standard treatment, second-line drugs should be considered, including mycophenolate mofetil, calcineurin inhibitors, mechanistic target of rapamycin (mTOR) inhibitors and biologic agents, which should be administered only in specialized hepatology centres. Liver transplantation is a life-saving option for those who progress to end-stage liver disease, although AIH can recur or develop de novo after transplantation. In-depth investigation of immune pathways and analysis of changes to the intestinal microbiota should advance our knowledge of the pathogenesis of AIH and lead to novel, tailored and better tolerated therapies.

Invariant natural killer T cell deficiency leads to the development of spontaneous liver inflammation dependent on γδT cells in mice

BACKGROUND

Immune tolerance is maintained in the liver, and perturbation of tolerance can lead to immune-mediated liver diseases such as autoimmune hepatitis (AIH). Invariant natural killer T (iNKT) cells and γδT cells have been shown to maintain immune homeostasis as regulatory cells and to play pathogenic roles in immune-mediated diseases as effector cells. We hypothesized that iNKT cells and γδT cells are involved in the maintenance of hepatic immune tolerance and immune-mediated liver disease.

METHODS

We measured liver inflammation and the cytokine profiles of liver mononuclear cells in BALB/c wild-type (WT) mice and BALB/c Jα18-deficient (KO) mice lacking iNKT cells. We also examined the role of γδT cells in AIH using liver tissue from AIH patients and control subjects.

RESULTS

Spontaneous liver inflammation, hepatocyte damage, and anti-nuclear-antibody production occurred in Jα18 KO mice but not in WT mice. Furthermore, liver mononuclear cells from Jα18 KO mice, but not those from WT mice, produced interleukin-17 (IL-17). γδT cells were the primary producers of the cytokine, and they were more abundant in the livers of Jα18 KO mice than in those of WT mice. In Jα18 KO mice, the administration of anti-γδT-cell-receptor antibody abolished liver inflammation, hepatocyte damage, and IL-17 production. γδT cells accumulated in the livers of AIH patients but not in those of the control subjects.

CONCLUSIONS

Our results suggest a protective role for iNKT cells, a pathologic role for γδT cells, and an association between these cells in the pathogenesis of AIH.

Transitioning from Idiopathic to Explainable Autoimmune Hepatitis

Autoimmune hepatitis lacks an identifiable cause, and its diagnosis requires the exclusion of etiologically defined diseases that resemble it. Insights into its pathogenesis are moving autoimmune hepatitis from an idiopathic to explainable disease, and the goal of this review is to describe the insights that are hastening this transition. Two types of autoimmune hepatitis are justified by serological markers, but they also have distinctive genetic associations (DRB1 and DQB1 genes) and autoantigens. DRB1 alleles are the principal susceptibility factors in white adults, and a six amino acid sequence encoded in the antigen-binding groove of class II molecules of the major histocompatibility complex can influence the selection of autoantigens. Polymorphisms, including variants of SH2B3 and CARD10 genes, may affect immune reactivity and disease severity. The cytochrome mono-oxygenase, CYP2D6, is the autoantigen associated with type 2 autoimmune hepatitis, and it shares homologies with multiple viruses that might promote self-intolerance by molecular mimicry. Chemokines, especially CXCL9 and CXCL10, orchestrate the migration of effector cells to sites of injury and are associated with disease severity. Cells of the innate and adaptive immune responses promote tissue damage, and possible deficiencies in the number and function of regulatory T cells may facilitate the injurious process. Receptor-mediated apoptosis is the principal mechanism of hepatocyte loss, and cell-mediated and antibody-dependent mechanisms of cytotoxicity also contribute. Insights that explain autoimmune hepatitis will allow triggering exogenous antigens to be characterized, risk management to be improved, prognostic indices to be refined, and site-specific therapeutic interventions to emerge.

Immunity, tolerance and autoimmunity in the liver: A comprehensive review

The hepatic immune system is constantly exposed to a massive load of harmless dietary and commensal antigens, to which it must remain tolerant. Immune tolerance in the liver is mediated by a number of specialized antigen-presenting cells, including dendritic cells, Kupffer cells, liver sinusoidal endothelial cells and hepatic stellate cells. These cells are capable of presenting antigens to T cells leading to T cell apoptosis, anergy, or differentiation into regulatory T cells. However, the hepatic immune system must also be able to respond to pathogens and tumours and therefore must be equipped with mechanisms to override immune tolerance. The liver is a site of accumulation of a number of innate lymphocyte populations, including natural killer cells, CD56(+) T cells, natural killer T cells, γδ T cells, and mucosal-associated invariant T cells. Innate lymphocytes recognize conserved metabolites derived from microorganisms and host cells and respond by killing target cells or promoting the differentiation and/or activation of other cells of the immune system. Innate lymphocytes can promote the maturation of antigen-presenting cells from their precursors and thereby contribute to the generation of immunogenic T cell responses. These cells may be responsible for overriding hepatic immune tolerance to autoantigens, resulting in the induction and maintenance of autoreactive T cells that mediate liver injury causing autoimmune liver disease. Some innate lymphocyte populations can also directly mediate liver injury by killing hepatocytes or bile duct cells in murine models of hepatitis, whilst other populations may protect against liver disease. It is likely that innate lymphocyte populations can promote or protect against autoimmune liver disease in humans and that these cells can be targeted therapeutically. Here I review the cellular mechanisms by which hepatic antigen-presenting cells and innate lymphocytes control the balance between immunity, tolerance and autoimmunity in the liver.

Cell mediators of autoimmune hepatitis and their therapeutic implications

Autoimmune hepatitis is associated with interactive cell populations of the innate and adaptive immune systems, and these populations are amenable to therapeutic manipulation. The goals of this review are to describe the key cell populations implicated in autoimmune hepatitis and to identify investigational opportunities to develop cell-directed therapies for this disease. Studies cited in PubMed from 1972 to 2014 for autoimmune hepatitis, innate and adaptive immune systems, and therapeutic interventions were examined. Dendritic cells can promote immune tolerance to self-antigens, present neo-antigens that enhance the immune response, and expand the regulatory T cell population. Natural killer cells can secrete pro-inflammatory and anti-inflammatory cytokines and modulate the activity of dendritic cells and antigen-specific T lymphocytes. T helper 2 lymphocytes can inhibit the cytotoxic activities of T helper 1 lymphocytes and limit the expansion of T helper 17 lymphocytes. T helper 17 lymphocytes can promote inflammatory activity, and they can also up-regulate genes that protect against oxidative stress and hepatocyte apoptosis. Natural killer T cells can expand the regulatory T cell population; gamma delta lymphocytes can secrete interleukin-10, stimulate hepatic regeneration, and induce the apoptosis of hepatic stellate cells; and antigen-specific regulatory T cells can dampen immune cell proliferation and function. Pharmacological agents, neutralizing antibodies, and especially the adoptive transfer of antigen-specific regulatory T cells that have been freshly generated ex vivo are evolving as management strategies. The cells within the innate and adaptive immune systems are key contributors to the occurrence of autoimmune hepatitis, and they are attractive therapeutic targets.

A new effect of IL-4 on human γδ T cells: promoting regulatory Vδ1 T cells via IL-10 production and inhibiting function of Vδ2 T cells

Interleukin 4 (IL-4) has a variety of immune functions, including helper T-cell (Th-cell) differentiation and innate immune-response processes. However, the impact of IL-4 on gamma delta (γδ) T cells remains unclear. In this study, we investigate the effects of IL-4 on the activation and proliferation of γδ T cells and the balance between variable delta 1 (Vδ1) and Vδ2 T cells in humans. The results show that IL-4 inhibits the activation of γδ T cells in the presence of γδ T-cell receptor (TCR) stimulation in a STAT6-dependent manner. IL-4 promoted the growth of activated γδ T cells and increased the levels of Vδ1 T cells, which in turn inhibited Vδ2 T-cell growth via significant IL-10 secretion. Vδ1 T cells secreted significantly less interferon gamma (IFNγ) and more IL-10 relative to Vδ2. Furthermore, Vδ1 T cells showed relatively low levels of Natural Killer Group 2D (NKG2D) expression in the presence of IL-4, suggesting that Vδ1 T cells weaken the γδ T cell-mediated anti-tumor immune response. For the first time, our findings demonstrate a negative regulatory role of IL-4 in γδ T cell-mediated anti-tumor immunity.

Role of gamma-delta (γδ) T cells in autoimmunity

γδ T cells represent a small population of overall T lymphocytes (0.5-5%) and have variable tissue distribution in the body. γδ T cells can perform complex functions, such as immune surveillance, immunoregulation, and effector function, without undergoing clonal expansion. Heterogeneous distribution and anatomic localization of γδ T cells in the normal and inflamed tissues play an important role in alloimmunity, autoimmunity, or immunity. The cross-talk between γδ T cells and other immune cells and phenotypic and functional plasticity of γδ T cells have been given recent attention in the field of immunology. In this review, we discussed the cellular and molecular interaction of γδ T cells with other immune cells and its mechanism in the pathogenesis of various autoimmune diseases.

Phenotypic and functional plasticity of gamma-delta (γδ) T cells in inflammation and tolerance

Gamma-delta T cells (γδ T cells) are an unique group of lymphocytes and play an important role in bridging the gap between innate and adaptive immune systems under homeostatic condition as well as during infection and inflammation. They are predominantly localized into the mucosal and epithelial sites, but also exist in other peripheral tissues and secondary lymphoid organs. γδ T cells can produce cytokines and chemokines to regulate the migration of other immune cells, can bring about lysis of infected or stressed cells by secreting granzymes, provide help to B cells and induce IgE production, can present antigen to conventional T cells, activate antigen presenting cells (APC) maturation, and are also known to produce growth factors that regulate the stromal cell function. γδ T cells spontaneously produce IFN-γ and IL-17 cytokines compared to delayed differentiation of Th1 and Th17 cells. In this review, we discussed the current knowledge about the mechanism of γδ T cell function including its mode of antigen recognition, and differentiation into various subsets of γδ T cells. We also explored how γδ T cells interact with different types of innate and adaptive immune cells, and how these interactions shape the immune response highlighting the plasticity and role of these cells-protective or pathogenic under inflammatory and tolerogenic conditions.

Potential regulatory role of in vitro-expanded Vδ1 T cells from human peripheral blood

γδ T cells represent a relevant proportion of T lymphocytes that express T cell receptors (TCRs) encoded by the γ and δ T cell receptor genes. Whereas the most circulating γδ T cell type, Vδ2 T cells, has been described and studied intensively, the potential role of Vδ1 T cells remains largely unclear. Here, we identified that expanded peripheral blood Vδ1 T cells stimulated with anti-human TCR Vδ1 monoclonal antibody (mAb) in vitro predominantly expressed forkhead box p3 (Foxp3). In addition, these cells also expressed other regulatory T cell-related molecules, such as CD25, glucocorticoid-induced TNFR family-related protein and cytotoxic T lymphocyte-associated protein-4 (CTLA-4), and held the potent capacity for the production of transforming growth factor beta 1 (TGF-β1). These autocrine and/or paracrine TGF-β1 could bind TGF-β1 receptors on Vδ1 T cells and induce sustained Foxp3 expression. Moreover, Foxp3 expression coincided with high CD25 expression. CD25(high) Vδ1 T cells exhibited stronger suppression on CD4(+) T cell proliferation compared with TGF-β1-induced CD25(high) CD4(+) regulatory T cells. Therefore, our phenotypic and functional analyses first demonstrate the potential regulatory property of anti-human TCR Vδ1 mAb-activated Vδ1 T cells. These results will broaden our understanding about the role of peripheral blood Vδ1 T cells under physical and pathological conditions.

Liver immunology

The liver is the largest organ in the body and is generally regarded by nonimmunologists as having little or no lymphoid function. However, such is far from accurate. This review highlights the importance of the liver as a lymphoid organ. Firstly, we discuss experimental data surrounding the role of liver as a lymphoid organ. The liver facilitates tolerance rather than immunoreactivity, which protects the host from antigenic overload of dietary components and drugs derived from the gut and it is instrumental to fetal immune tolerance. Loss of liver tolerance leads to autoaggressive phenomena, which if not controlled by regulatory lymphoid populations, may lead to the induction of autoimmune liver diseases. Liver-related lymphoid subpopulations also act as critical antigen-presenting cells. The study of the immunological properties of liver and delineation of the microenvironment of the intrahepatic milieu in normal and diseased livers provides a platform to understand the hierarchy of a series of detrimental events that lead to immune-mediated destruction of the liver and the rejection of liver allografts. The majority of emphasis within this review will be on the normal mononuclear cell composition of the liver. However, within this context, we will discuss selected, but not all, immune-mediated liver disease and attempt to place these data in the context of human autoimmunity.

The role of vitamin d in autoimmune hepatitis

Autoimmune hepatitis is an inflammation of the liver characterized by the presence of peri-portal hepatitis, hypergammaglobulinemia, and the serum autoantibodies. The disease is classified into 2 distinct types according to the nature of auto-antibodies. Disturbances of the calcium-parathyroid hormone-vitamin D axis are frequently associated with chronic liver disease. Patients with AIH have a high prevalence of vitamin D deficiency. Genetic studies have provided the opportunity to determine which proteins link vitamin D to AIH pathology, namely, the major histocompatibility complex class II molecules, vitamin D receptors, toll-like receptors, cytotoxic T lymphocyte antigen-4, cytochrome P450 CYP2D6, regulatory T cells (Tregs) and the forkhead/winged helix transcription factor 3. Vitamin D also exerts its effect on AIH through non-genomic factors, namely, mitogen-activated protein kinase signaling pathways, γδT cells, interferon-gamma nitric oxide synthase, and reactive oxygen stress. In conclusion, vitamin D may have a beneficial role in AIH and improves liver function in concanavalin A-induced mouse AIH. Calcitriol is best used for AIH because it is the active form of a vitamin D3 metabolite and its receptors are present in sinusoidal endothelial cells, Kupffer cells, stellate cells of normal livers, and the biliary cell line.

Pathogenesis of autoimmune hepatitis

The mechanisms underlying the pathogenesis of autoimmune hepatitis are not fully understood, though there is growing evidence that genetic predisposition, molecular mimicry and/or impairment of regulatory T-cells are involved in the initiation and perpetuation of the autoimmune liver attack. The histological picture of interface hepatitis, characterized by a dense portal mononuclear cell infiltrate, was the first to suggest an autoaggressive cellular immune attack in the pathogenesis of this condition. Liver damage is likely to be orchestrated by CD4(pos) T-cells recognizing an autoantigenic liver peptide. For autoimmunity to arise, the peptide must be presented by antigen-presenting cells to naïve CD4(pos) T-helper (Th0) cells. Once activated, Th0-cells can differentiate into Th1-, Th2-, or Th17-cells, initiating a cascade of immune reactions that are determined by the cytokines they produce. Autoantigen recognition and the above effector mechanisms are opposed by regulatory T-cells, a cell subset numerically and functionally impaired in autoimmune hepatitis.

A multifaceted imbalance of T cells with regulatory function characterizes type 1 autoimmune hepatitis

Immunotolerance is maintained by regulatory T cells (Tregs), including CD4(+)CD25(hi), CD8(+)CD28(-), gammadelta, and CD3(+)CD56(+) [natural killer T (NKT)] cells. CD4(+)CD25(hi) cells are impaired in children with autoimmune hepatitis (AIH). Little is known about Tregs in adults with AIH. The aim of this study was to investigate the frequency and function of Treg subsets in adult patients with AIH during periods of active disease and remission. Forty-seven AIH patients (16 with active disease and 31 in remission) and 28 healthy controls were studied. Flow cytometry was used to evaluate surface markers and function-related intracellular molecules in gammadelta, CD8(+)CD28(-), NKT, and CD4(+)CD25(hi) cells. CD4(+)CD25(hi) T cell function was determined by the ability to suppress proliferation and interferon gamma (IFN-gamma) production by CD4(+)CD25(-) target cells. Liver forkhead box P3-positive (FOXP3(+)) cells were sought by immunohistochemistry. In AIH patients, particularly during active disease, CD4(+)CD25(hi) T cells were fewer, expressed lower levels of FOXP3, and were less effective at inhibiting target cell proliferation versus healthy controls. Moreover, although the numbers of CD8(+)CD28(-) T cells were similar in AIH patients and healthy controls, NKT cells were numerically reduced, especially during active disease, and produced lower quantities of the immunoregulatory cytokine interleukin-4 versus controls. In contrast, gammadelta T cells in AIH patients were more numerous versus healthy controls and had an inverted Vdelta1/Vdelta2 ratio and higher IFN-gamma and granzyme B production; the latter was correlated to biochemical indices of liver damage. There were few FOXP3(+) cells within the portal tract inflammatory infiltrate.

CONCLUSION

Our data show that the defect in immunoregulation in adult AIH is complex, and gammadelta T cells are likely to be effectors of liver damage.

Lymphocyte recruitment and homing to the liver in primary biliary cirrhosis and primary sclerosing cholangitis

The mechanisms operating in lymphocyte recruitment and homing to liver are reviewed. A literature review was performed on primary biliary cirrhosis (PBC), progressive sclerosing cholangitis (PSC), and homing mechanisms; a total of 130 papers were selected for discussion. Available data suggest that in addition to a specific role for CCL25 in PSC, the CC chemokines CCL21 and CCL28 and the CXC chemokines CXCL9 and CXCL10 are involved in the recruitment of T lymphocytes into the portal tract in PBC and PSC. Once entering the liver, lymphocytes localize to bile duct and retain by the combinatorial or sequential action of CXCL12, CXCL16, CX3CL1, and CCL28 and possibly CXCL9 and CXCL10. The relative importance of these chemokines in the recruitment or the retention of lymphocytes around the bile ducts remains unclear. The available data remain limited but underscore the importance of recruitment and homing.

The immunobiology of primary sclerosing cholangitis

Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease histologically characterized by the presence of intrahepatic and/or extrahepatic biliary duct concentric, obliterative fibrosis, eventually leading to cirrhosis. Approximately 75% of patients with PSC have inflammatory bowel disease. The male predominance of PSC, the lack of a defined, pathogenic autoantigen, and the potential role of the innate immune system suggest that it may be due to dysregulation of immunity rather than a classic autoimmune disease. However, PSC is associated with several classic autoimmune diseases, and the strongest genetic link to PSC identified to date is with the human leukocyte antigen DRB01*03 haplotype. The precise immunopathogenesis of PSC is largely unknown but likely involves activation of the innate immune system by bacterial components delivered to the liver via the portal vein. Induction of adhesion molecules and chemokines leads to the recruitment of intestinal lymphocytes. Bile duct injury results from the sustained inflammation and production of inflammatory cytokines. Biliary strictures may cause further damage as a result of bile stasis and recurrent secondary bacterial cholangitis. Currently, there is no effective therapy for PSC and developing a rational therapeutic strategy demands a better understanding of the disease.

Disproportionally strong increase of B cells in inflammatory cerebrospinal fluid of dogs with Steroid-responsive Meningitis-Arteritis

Steroid-responsive Meningitis-Arteritis (SRMA) is a systemic inflammatory disease of juvenile to young adult dogs with a relapsing course and most prominent manifestation in the cervical meninges. Immunophenotyping and flow cytometric measurement of lymphocytes in peripheral blood (PB) and CSF was performed in the acute phase of SRMA (n=12) and during glucocorticosteroid treatment (n=10). Values were compared to those from dogs with other neurologic diseases (n=63) and healthy individuals (n=7). Dogs with SRMA had high CD4:CD8alpha ratios in PB and low T:B cell ratios in PB and CSF suggesting that a T(H)2-mediated immune response occurs. The T:B cell ratio in CSF was markedly lower than that in PB indicating that either a selective recruitment of B cells or, alternatively, their strong intrathecal proliferation takes place. SRMA appears to be a valuable animal model for the investigation of compartmentalization of immune responses and for studies on differences in local central nervous system and systemic immune responses.

Autoimmune hepatitis: evolving concepts

The liver is continuously exposed to a large antigenic load that includes pathogens, toxins, tumor cells and dietary antigens. A loss of tolerance against its own antigens may result in autoimmune hepatitis (AIH). The current paradigm holds that the disease is the result of self-perpetuating autoimmune process triggered by yet unknown factors (infections, chemicals, drugs) in a genetically susceptible host. To date, several putative hepatocellular surface antigens have been identified: P450-IID6 (recognized by the anti-LKM-1 autoantibodies) a membrane bound asialoglycoprotein receptor (a liver-specific membrane protein), a cytosolic UGA-suppressor tRNA associated protein (recognized by anti-SMA and anti-LP antibodies) and argininosuccinate lysate and formiminotransferase cyclodeaminase (recognized by ant-LC1 antibodies). In contrast to other chronic hepatitides patients with AIH display significant T cell hypereactivity to autologous liver antigens. Tissue injury seems to be mediated by CD4+ or CD8+ T cells and/or by antibody-dependent cell mediated cytotoxicity.

Natural T cells in the human liver: cytotoxic lymphocytes with dual T cell and natural killer cell phenotype and function are phenotypically heterogenous and include Valpha24-JalphaQ and gammadelta T cell receptor bearing cells

The adult liver contains lymphocytes with a unique phenotypic distribution compared to blood and other organs. We have characterized a human lymphocyte population that exhibits dual T cell and natural killer (NK) cell phenotype and function, denoted natural T (NT) cells, in nine normal adult liver specimens. Flow cytometry revealed that up to 55% (mean 27%) of hepatic (but <6% of peripheral) CD3+ lymphocytes expressed CD56, CD161 and/or one or more of the killer inhibitory receptors (KIR) p58.1, p58.2, p70 and CD94. NK function was attributed to the CD3+CD56+ cells by the demonstration that hepatic, but not peripheral, CD3+ lymphocytes could be induced to lyse NK-sensitive K562 target cells, while CD56- cells from both compartments could not. Three color flow cytometric analysis of fresh hepatic cells indicated that CD3+CD56+ NT cells can be either CD8+, CD4+ or CD4 CD8-, they express alphabeta or gammadelta T cell receptors (TCR) and CD161 and KIRs, but rarely CD16. Hepatic NT cells predominantly express the mature/activated CD45RO and CD56dim phenotypes. Analysis of mRNA production by isolated NT cells indicated a preferential usage of the invariant CD1-restricted Valpha24-JalphaQ TCR. The presence of such large numbers of chronically activated NT cells provides compelling evidence that the liver has unique immunoregulatory functions.

Resident human hepatic lymphocytes are phenotypically different from circulating lymphocytes

BACKGROUND/AIMS

Murine and human studies have documented the existence of subpopulations of lymphocytes in particular tissues that differ phenotypically and functionally from those in peripheral blood and may mature locally. Since little is known about lymphocyte subpopulations in the normal human liver, we have analysed the surface phenotypes of lymphocytes isolated from liver specimens taken from 15 donors at the time of liver transplantation, and compared these with those of peripheral blood lymphocytes.

METHODS

Hepatic lymphocytes were prepared by mechanical dissociation and enzymatic digestion of liver tissue. The cells were stained with a panel of monoclonal antibodies (CD3, CD4, CD8, CD19, CD56, gammadeltaTCR, alphabetaTCR, CD8alpha-chain, CD8alphabeta dimer), and analysed by flow cytometry. In situ characterisation of hepatic lymphocytes was by haematoxylin and eosin staining of fixed liver sections and by immunohistochemical staining for common leukocyte antigen and CD3.

RESULTS

Significant numbers of hepatic T lymphocytes were localised to the portal tracts and parenchyma of normal liver specimens. Flow cytometry revealed that the CD4/CD8 ratio (1:3.5) was consistently reversed compared with that in peripheral blood (2:1). Other lymphocyte populations identified include double positive CD3+CD4+CD8+ cells which accounted for a mean of 5.5% (range 3-11.6%) of hepatic CD3+ cells compared with 1.3% in blood (range 0.7-3.6%; p < 0.007), and double negative CD3+ CD4-8- cells (14.5%; range 2.7-29% compared with 5.0%; range 2.1-10.8%, p < 0.02). Over 15% (range 6.8-34%) of all hepatic CD3+ cells expressed a gammadeltaTCR compared to 2.7% (range 0.9-4.7%) of CD3+ peripheral blood lymphocytes (p < 0.004) and almost 50% of these coexpressed CD8. The CD8 alpha-chain was expressed without the beta-chain (CD8alpha+beta-) by 15.4% (range 4-29.1%) of hepatic T cells, but this phenotype was undetectable among peripheral blood lymphocytes (p < 0.009). Cells expressing both the T cell marker CD3 and the natural killer cell marker CD56 constituted 31.6% (range 14-54%) of all hepatic CD3+ lymphocytes but were rarely present amongst peripheral blood lymphocytes (0-6%; p < 0.0001).

CONCLUSIONS

These data are the first to describe and quantify unconventional T lymphocyte subpopulations in the normal adult human liver which may have specialised functions in regional immune responses and which may differentiate locally. These findings have important implications for our understanding of hepatic immunoregulation and the pathogenic mechanisms involved in viral and immune-mediated liver disease and allograft rejection.

Gamma delta cells regulate autoimmunity

Gamma delta cells are attractive candidates for mediators of autoimmune disease. They can expand in germ-free mice, probably through recognition of autoantigens, and gamma delta-cell-deficient mice, unlike mice deficient in alpha beta T cells or B cells, show no severe defects in the immune response to foreign antigen challenge. A capacity of gamma delta cells to effect or regulate tissue damage is also plausible, given their ready localization to tissues, and their myriad of effector functions. Added to this, attempts to reconstruct the physiological course of autoimmune diseases with only autoreactive alpha beta T cells seem invariably to fall short for lack of other unidentified players. Gamma delta cells and their putative ligands have been linked to autoimmune conditions, and recent experiments confirm that gamma delta cells play a significant role in autoimmune disease in vivo.

Gamma delta + T cells in Wilson's disease

Little is currently known about the role of gamma delta + T cells in disease pathogenesis. We have demonstrated elevated levels of gamma delta + T cells in the peripheral blood and cerebrospinal fluid of patients with Wilson's disease compared with other neurological diseases. The percentage of V delta 1 +/ gamma delta + T cells was between 20% and 50% in all patient groups; gamma delta + T cells in blood correlated with copper concentrations. The antigen reactivity of gamma delta + T cells and how the antigens relate to the gamma delta + T cells found in WD remains unknown. It remains unclear whether there is a direct reason for the elevated gamma delta + T cells population found in WD. Immunohistochemistry of frozen autopsy material from brain and liver of WD patients could allow exact localization of gamma delta + T cells and heat shock proteins in future studies.

Detection of antibodies to 65 KD heat shock protein and to human superoxide dismutase in autoimmune hepatitis-molecular mimicry between 65 KD heat shock protein and superoxide dismutase

The antibody to 65 KD mycobacterial heat shock protein (HSP65) and antibody to human superoxide dismutase (H-SOD) were measured by ELISA in patients with autoimmune hepatitis (AIH), and results were compared with those of patients with chronic active hepatitis C (CAH-C) or systemic lupus erythematosus (SLE) and normal subjects (NS). Patients with AIH had significantly higher OD values of anti-HSP65 antibody and anti-H-SOD antibody compared with those of patients with CAH-C or SLE and NS. OD values of anti-HSP65 antibody were correlated with those of anti-SOD antibody. Affinity-purified anti-SOD antibody reacted with HSP65. Analysis of the amino acid sequence of human SOD showed that 7 segments, corresponding to r to 25 amino acid residues, exhibited 50 to 71% homology with that of my mycobacterial HSP65.

Phenotypical characterization of peripheral blood T cells in patients with coeliac disease: elevation of antigen-primed CD45RO+ T lymphocytes

Increased numbers of gamma delta T-cell-receptor-bearing (TCR gamma delta +) lymphocytes are present in the small intestinal epithelium of patients with coeliac disease (CoD). In this study the phenotypic characteristics of peripheral blood T cells from 14 untreated CoD patients and 14 healthy age- and sex-matched controls were determined with special emphasis on TCR gamma delta + lymphocytes. We also studied samples taken from 15 CoD patients who were on gluten-free diet (GFD). Two- and three-colour flow cytometry analyses were performed using a whole-blood lysing method. There was no significant difference between the percentages of TCR gamma delta + lymphocytes in patients and controls. However, the amount of delta TCS1+ lymphocytes was significantly lowered in untreated patients (0.48 +/- 0.42% in CoD versus 0.86 +/- 0.57% in controls, P < 0.05). The percentage of CD45RO+ T cells, which are a primed population of T cells including memory cells, was significantly raised in the peripheral blood of untreated patients. This phenomenon was most prominent within the TCR gamma delta + population (83.9 +/- 12.2% in CoD versus 65.5 +/- 14.7% in controls, P < 0.01), but the same applies to CD45RO+ TCR alpha beta + and delta TCS1+ T cells. In patients on GFD these changes seem to be at least partly corrected. Antigen-primed CD45RO+ T cells have been shown to accumulate in the jejunal epithelium of patients with untreated CoD. The enhanced 'memory activity' also found in the peripheral blood of untreated CoD patients may result from a continuous antigenic stimulus and this stimulus could be gluten triggered.

T cell receptor usage in autoimmune disease

Activated T-cells are believed to play a critical role in the pathogenesis of autoimmune disease. In experimental allergic encephalomyelitis (EAE), an animal model resembling human multiple sclerosis (MS), there is evidence that T cells reactive to myelin basic protein mediate an inflammatory response within the central nervous system leading to demyelination. Furthermore, encephalitogenic T cells express TCR with highly restricted V gene usage and consequently specific forms of immunotherapy directed against V gene products have been successful in preventing and treating EAE. These findings prompted studies into the analysis of TCR repertoire expression in human autoimmune diseases in an attempt to identify the TCR usage of autoreactive and potentially pathogenic T cells. However, this has proved difficult as the autoantigens that drive the T cell response in most human autoimmune disorders are unknown. This review examines the data that have accumulated over the past few years on TCR usage in human autoimmune diseases and is focused largely on rheumatoid arthritis and MS.

Gamma delta T cell distribution in cerebrospinal fluid and peripheral blood of patients with multiple sclerosis

The distribution of gamma delta T cells was determined in peripheral blood of 50 patients in acute relapse of clinically definite multiple sclerosis (MS), 8 patients with primary progressive MS, 26 patients with inflammatory neurological disease (IND), 33 patients with non-inflammatory neurological disease (NIND) and 31 healthy subjects. Paired cerebrospinal fluid samples were obtained from 37 patients with relapsing-remitting MS, 2 patients with primary progressive MS, 14 with IND and 18 with NIND. The monoclonal antibodies pan-alpha beta TCR, TCR delta 1, delta TCS1 and anti-delta V2(a) which identify alpha beta T cells, gamma delta T cells, V delta 1, and V delta 2 gene products respectively, were used to define the T cell receptor repertoire. gamma delta T cells expressed as a percentage of CD3+ lymphocytes were lower in MS CSF compared to NIND CSF (3.4% +/- 0.5 versus 7.3% +/- 1.4; p < 0.001). This was due to a lower MS CSF. Peripheral blood levels of gamma delta T cells were normal in each study group. CD45RA expression was increased on gamma delta T cells in CSF of each patient group when compared with the paired blood samples. These results suggest that V delta 1 + and V delta 2 + gamma delta T cells with altered CD45 expression are reduced in CSF of patients with established MS. This finding may be related to sequestration or apoptosis of gamma delta T cells within active MS lesions.

Increase of circulating gamma/delta T lymphocytes in the peripheral blood of patients affected by active inflammatory bowel disease

In order to study the role of gamma/delta T cells in the pathogenesis of inflammatory bowel disease (IBD) in humans, we measured the percentage of these cells in the peripheral blood, assessed the ratio of the non-disulphide-linked (delta TCS1) type of T cell receptor (TCR) in the total gamma/delta T cells, studied the co-expression of gamma/delta TCR and accessory molecules CD8 and CD16, and compared these data with both the type and the activity of the disease. Percentage levels and absolute numbers of gamma/delta+ T cells were higher in active patients than in controls (P < 0.05), mainly as a result of an increase of V delta 1+ (delta TCS1) T cell subset (P < 0.05). This trend was strongly retained independently of disease activity and clinical picture. An increased percentage of TCR delta 1+/CD16+ cells was observed in our patients compared with controls (P < 0.05). In contrast, no difference was observed as far as the TCR delta 1+/CD8+ cells were concerned. These results suggest that IBD is associated with an expansion of gamma/delta T cells in peripheral blood, which may play a role in the pathogenesis of these disorders.

Characteristics of HPRT-mutant T cell lines in a lupus patient treated with cyclophosphamide

This report describes T cell lines derived from a patient with subacute cutaneous lupus after treatment with intravenous pulse cyclophosphamide. We selected for mitotically active, hypoxanthine-guanine phosphoribosyltransferase-deficient (HPRT-) T cells, by culture in a selective medium containing 6-thioguanine. When HPRT- cell lines were derived 6 days after pulse cyclophosphamide (CYC) treatment, they were predominantly CD8+ and T cell receptor (TCR) gamma/delta+, producing interferon-gamma (IFN gamma). Cell lines derived 21 days after CYC treatment were CD4+, TCR alpha/beta+ and produced both IFN gamma and interleukin-4. These results support a possible role for gamma/delta+ T cells in subacute cutaneous lupus and suggest a mechanism for the therapeutic effect of CYC.

V delta 1 gene usage, interleukin-2 receptors and adhesion molecules on gamma delta+ T cells in inflammatory diseases of the nervous system

This study investigates the expression of T cell receptor V delta 1 chain, interleukin-2 receptor alpha-chain (CD25) and adhesion molecules ICAM-1 (CD54), LFA-1 (CD11a/18) and CD44 on gamma delta+ T cells by three-color flow cytometry on cerebrospinal fluid (CSF) and blood cells in patients with multiple sclerosis (MS), other inflammatory neurological diseases (OIND) and other neurological diseases (OND). Of gamma delta + T cells in CSF and blood, 20-40% belonged to the 'epithelial' V delta 1 subtype. MS patients had the lowest levels in both CSF and blood, but the differences between the patient groups were not significant. The activation markers CD25 and CD54 were expressed by only a small proportion of gamma delta+ T cells and in a minority of patients. Although the occurrence of CD25+ and CD54+ gamma delta+ T cells was somewhat higher in CSF than in blood and in inflammatory diseases than in controls, the small numbers of CD25+ and CD54+ gamma delta+ T cells preclude establishing differences amongst compartments and patient groups. The adhesion molecules CD11a/18 and CD44 were constitutively expressed on all T cells. Therefore, we compared the relative antigen density per cell as measured by the relative fluorescence index (RFI) between CSF and blood, between the patient groups and between gamma delta+ and total T cells. The only difference encountered was a slightly higher expression of adhesion molecules on gamma delta+ compared to total T cells, with preference to MS patients. In conclusion, the V delta 1+ subtype of gamma delta+ T cells does not dominate in the CSF compartment.(ABSTRACT TRUNCATED AT 250 WORDS)

T cell clones generated from patients with type 1 diabetes using interleukin-2 proliferate to human islet antigens

T lymphocytes are implicated in the pathogenesis of Type 1 (insulin dependent) diabetes. Activated T lymphocytes expressing IL-2 receptors are found at increased levels in the peripheral blood in the prediabetic period, at diagnosis and for several months after the onset of the disease, but their role in the pathogenesis of the disease is not known. We have used co-culture of peripheral blood lymphocytes with IL-2 alone to selectively generate T cell clones from the in vivo activated T cell population, and examined the phenotype and antigen specificity of the clones derived. From 3 patients with newly-diagnosed Type 1 diabetes 184 clones were generated, the majority of which (39%) were CD4+TCR alpha beta+, whilst 31% were CD8+TCR alpha beta+. From 2 healthy control subjects 90 clones were obtained, of which 62% were CD4+TCR alpha beta+ and 33% were CD8+TCR alpha beta+. Antigen specificity was examined in 46 clones from the patients and 44 from the control subjects in proliferation assays, using as antigens homogenate of human islets of Langerhans, human islet membrane preparation and human liver membrane preparation. Three clones (all CD4+TCR alpha beta+) from the patients, but none from the control subjects, proliferated in a dose dependent fashion in response to stimulation with human islet homogenate presented by autologous APCs, but to neither of the other autoantigen preparations. Our results demonstrate that a relatively high proportion (7%) of T lymphocytes activated in vivo recognise human islet antigens, indicating that they may have a role in the pathogenesis of the disease.

Lymphocytes bearing the gamma delta T cell receptor in acute Brucella melitensis infection

A phenotypical analysis carried out by indirect immunofluorescence and two-color cytofluorometry showed that the number of lymphocytes bearing the gamma delta T cell receptor (TcR) heterodimer was dramatically increased in the blood of six children with Brucella melitensis infection. Most in vivo expanded gamma delta T cells reacted with a monoclonal antibody which identifies V delta 2 gene products and a significant proportion expressed CD25 and HLA-DR activation antigens. In addition, whereas only a few gamma delta T lymphocytes were CD8+, nearly all were CD4-. Highly enriched populations of both alpha beta and gamma delta T cells were obtained by negative immunoselection from three subjects with brucellosis sampled during convalescence. Despite the different form of their TcR, the proliferation of these two major T cell subsets in response to a mitogenic anti-CD3 monoclonal reagent (OKT3) was optimal. In contrast, alpha beta, but not gamma delta, T lymphocytes proliferated vigorously in response to the antigenic stimulus elicited by heat-killed Brucella. Further studies are, therefore, needed to determine whether the selective expansion of the gamma delta T cell subpopulation observed during the clinical course of the infection is driven by antigenic determinant(s) borne by the pathogen in vivo or is due to host-derived stimuli, such as autologous heat-shock proteins expressed on the surface of the infected cells.