Cell Hyperreactivity Research Articles

Essential role of E3 ubiquitin ligase activity of GRAIL in T cell functions (P1111)

Abstract T cells are the master regulators of adaptive immune responses, and many autoimmune diseases arise due to a breakdown of self-tolerance in T cells. Understanding of the molecular mechanisms underlying T cell tolerance will lead to development of pharmacological approaches either to promote the tolerance state in terms of autoimmunity or to break tolerance in cancer. E3 ubiquitin ligases have been placed among the essential molecules involved in the regulation of T cell functions and T cell tolerance. We as well as other groups have reported that T cells activated in the absence of both CD28 and ICOS costimulation developed into tolerant T cells, associated with markedly upregulated expression of the E3 ubiquitin ligase GRAIL. In order to understand the physiological function of GRAIL, we generated mice deficient in Grail by replacing region that encompassing most of the RING domain and responsible for E3 ubiquitin activity. Remarkably, genetic inactivation of E3 ubiquitin ligase function of GRAIL led to T cell hyper-responsiveness to TCR/CD3z signaling and their independency to costimulation for activation. As a result, GRAIL-deficient mice were more predisposing to autoimmune diseases. On the other hand, modulation of GRAIL function helped to boost T cell immune responses to cancer, and, therefore, mediate tumor rejection. Thus, modulation of the E3 ligase activity of GRAIL might be an important approach to control T cell functions in autoimmunity or cancer.

NKG2D Mediates NK Cell Hyperresponsiveness and Influenza-Induced Pathologies in a Mouse Model of Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is characterized by peribronchial and perivascular inflammation and largely irreversible airflow obstruction. Acute disease exacerbations, due frequently to viral infections, lead to enhanced disease symptoms and contribute to long-term progression of COPD pathology. Previously, we demonstrated that NK cells from cigarette smoke (CS)-exposed mice exhibit enhanced effector functions in response to stimulating cytokines or TLR ligands. In this article, we show that the activating receptor NKG2D is a key mediator for CS-stimulated NK cell hyperresponsiveness, because CS-exposed NKG2D-deficient mice (Klrk1(-/-)) did not exhibit enhanced effector functions as assessed by cytokine responsiveness. NK cell cytotoxicity against MHC class I-deficient targets was not affected in a COPD model. However, NK cells from CS-exposed mice exhibit greater cytotoxic activity toward cells that express the NKG2D ligand RAET1ε. We also demonstrate that NKG2D-deficient mice exhibit diminished airway damage and reduced inflammation in a model of viral COPD exacerbation, which do not affect viral clearance. Furthermore, adoptive transfer of NKG2D(+) NK cells into CS-exposed, influenza-infected NKG2D-deficient mice recapitulated the phenotypes observed in CS-exposed, influenza-infected wild-type mice. Our findings indicate that NKG2D stimulation during long-term CS exposure is a central pathway in the development of NK cell hyperresponsiveness and influenza-mediated exacerbations of COPD.

Letter by Yasue et al Regarding Article, “Mechanisms of Coronary Artery Spasm”

To the Editor: We welcome the appearance of the article “Mechanisms of Coronary Artery Spasm” by Lanza and colleagues in Circulation ,1 because coronary artery spasm (CAS) has been underestimated or even misunderstood in Western countries. However, we are concerned that their conclusion on the pathogenesis of CAS might lead to some misunderstandings. We think that it is a matter of course that hyperreactivity of smooth muscle cells, not impairment of endothelium itself, is responsible for CAS.1 The issue is what underlies smooth muscle cell hyperreactivity. We think that chronic endothelial injury or nitric oxide (NO) deficiency leads to coronary artery remodeling with resulting smooth muscle cell hyperplasia and hyperreactivity, thrombogenicity, oxidative stress, and chronic …

Desmin Regulates Airway Smooth Muscle Hypertrophy through Early Growth-responsive Protein-1 and MicroRNA-26a

Bronchial biopsies of asthmatic patients show a negative correlation desmin expression in airway smooth muscle cell (ASMC) and airway hyperresponsiveness. We previously showed that desmin is an intracellular load-bearing protein, which influences airway compliance, lung recoil, and airway contractile responsiveness (Shardonofsky, F. R., Capetanaki, Y., and Boriek, A. M. (2006) Am. J. Physiol. Lung Cell. Mol. Physiol. 290, L890-L896). These results suggest that desmin may play an important role in ASMC homeostasis. Here, we report that ASMCs of desmin null mice (ASMCs(Des-/-)) show hypertrophy and up-regulation microRNA-26a (miR-26a). Knockdown of miR-26a in ASMCs(Des-/-) inhibits hypertrophy, whereas enforced expression of miR-26a in ASMCs(Des+/+) induces hypertrophy. We identify that Egr1 (early growth responsive protein-1) activates miR-26a promoter via enhanced phosphorylation of Erk1/2 in ASMCs(Des-/-). We show glycogen synthase kinase-3β (GSK-3β) as a target gene of miR-26a. Moreover, induction of ASMCs(Des-/-) hypertrophy by the Erk-1/2/Egr-1/miR-26a/GSK-3β pathway is consistent in human recombinant ASMCs, which stably suppresses 90% endogenous desmin expression. Overall, our data demonstrate a novel role for desmin as an anti-hypertrophic protein necessary for ASMC homeostasis and identifies desmin as a novel regulator of microRNA.

The autoimmune disease–associated PTPN22 variant promotes calpain-mediated Lyp/Pep degradation associated with lymphocyte and dendritic cell hyperresponsiveness

A variant of the PTPN22-encoded Lyp phosphatase (Lyp620W) confers risk for autoimmune disease, but the mechanisms underlying this association remain unclear. We show here that mice expressing the Lyp variant homolog Pep619W manifest thymic and splenic enlargement accompanied by increases in T-cell number, activation and positive selection and in dendritic- and B-cell activation. Although Ptpn22 (Pep) transcript levels were comparable in Pep619W and wild-type Pep619R mice, Pep protein levels were dramatically reduced in the mutant mice, with Pep619W protein being more rapidly degraded and showing greater association with and in vitro cleavage by calpain 1 than Pep619R. Similarly, levels of the Lyp620W variant were decreased in human T and B cells, and its calpain binding and cleavage were increased relative to wild-type Lyp620R. Thus, calpain-mediated degradation with consequently reduced Lyp/Pep expression and lymphocyte and dendritic cell hyperresponsiveness represents a mechanism whereby Lyp620W may increase risk for autoimmune disease.

In vivo effects of the anti–interleukin‐6 receptor inhibitor tocilizumab on the B cell compartment

Interleukin-6 (IL-6) receptor inhibition by tocilizumab was recently licensed for the treatment of rheumatoid arthritis (RA). IL-6 induces in vitro differentiation of B cells into antibody-forming cells; however, the in vivo effects of IL-6 inhibition on the B cell compartment are currently not known. The purpose of this study was to examine this feature. Sixteen patients with active RA were treated in an open-label study with tocilizumab (8 mg/kg every 4 weeks). Immunophenotyping was performed at baseline, week 12, and week 24. Memory B cell subsets declined significantly during tocilizumab therapy. Preswitch memory B cells decreased from a median of 19.6% to 12.3% at week 24 and postswitch memory B cells declined from a median of 18.6% to 15.0% at week 24 (P = 0.04). In parallel, CD19+IgA+ and CD19+IgG+ B cells decreased significantly. The proportion of IgA-expressing B cells fell from a median of 9.2% at baseline to 4.3% at week 12 and to 3.6% at week 24 (P = 0.01). IgG+ B cells declined from a median of 6.7% at baseline to 4.9% at week 12 (P = 0.007) and 2.8% at week 24 (P = 0.01). In parallel, serum levels of IgA and IgG were significantly diminished at week 24 (P < 0.05). There was a good correlation between relative and absolute numbers of IgA+ B cells with serum IgA at week 24. Tocilizumab induced a significant reduction in the frequency of peripheral preswitch and postswitch memory B cells. In addition, the number of IgG+ and IgA+ B cells declined and correlated well with reduced serum immunoglobulin levels. The data indicate that IL-6 blockade affects the B cell hyperreactivity in RA patients.

Inhibition of mTOR blocks the anti-inflammatory effects of glucocorticoids in myeloid immune cells

AbstractA central role for the mammalian target of rapamycin (mTOR) in innate immunity has been recently defined by its ability to limit proinflammatory mediators. Although glucocorticoids (GCs) exert potent anti-inflammatory effects in innate immune cells, it is currently unknown whether the mTOR pathway interferes with GC signaling. Here we show that inhibition of mTOR with rapamycin or Torin1 prevented the anti-inflammatory potency of GC both in human monocytes and myeloid dendritic cells. GCs could not suppress nuclear factor-κB and JNK activation, the expression of proinflammatory cytokines, and the promotion of Th1 responses when mTOR was inhibited. Interestingly, long-term activation of monocytes with lipopolysaccharide enhanced the expression of TSC2, the principle negative regulator of mTOR, whereas dexamethasone blocked TSC2 expression and reestablished mTOR activation. Renal transplant patients receiving rapamycin but not those receiving calcineurin inhibitors displayed a state of innate immune cell hyper-responsiveness despite the concurrent use of GC. Finally, mTOR inhibition was able to override the healing phenotype of dexamethasone in a murine lipopolysaccharide shock model. Collectively, these data identify a novel link between the glucocorticoid receptor and mTOR in innate immune cells, which is of considerable clinical importance in a variety of disorders, including allogeneic transplantation, autoimmune diseases, and cancer.

Anti-asthmatic effect of schizandrin on OVA-induced airway inflammation in a murine asthma model

Asthma comprises a triad of reversible airway obstruction, bronchial smooth muscle cell hyperreactivity to bronchoconstrictors, and chronic bronchial inflammation. Clinical and experimental findings have established eosinophilia as a sign of allergic disorders. In the present investigation, we evaluated the anti-asthmatic effects of schizandrin and its underlying mechanisms in an in vivo murine asthmatic model. To accomplish this, female BALB/c mice were sensitized and challenged with ovalbumin (OVA), and examined for the following typical asthmatic reactions: increased numbers of eosinophils and other inflammatory cells in bronchoalveolar lavage fluid (BALF); production of Th1 cytokines (such as tumor necrosis factor (TNF)-α in BALF); production of Th2 cytokines (such as interleukin IL-4 and IL-5) in BALF; presence of total and OVA-specific immunoglobulins (Ig)E in serum; presence of oxidative stress; hyperplasia of goblet cells in the lung; and marked influx of inflammatory cells into the lung. Our results collectively show that schizandrin exerts profound inhibitory effects on accumulation of eosinophils into the airways and reduces the levels of IL-4, IL-5, IFN-γ, and TNF-α in BALF. Additionally, schizandrin suppresses the production of reactive oxygen species (ROS) in a dose-dependent manner, and inhibits goblet cell hyperplasia and inflammatory cell infiltration in lung tissue. Thus, schizandrin has anti-asthmatic effects, which seem to be partially mediated by reduction of oxidative stress and airway inflammation, in a murine allergic asthma model. These results indicate that schizandrin may be an effective novel therapeutic agent for the treatment of allergic asthma.

Selective Preservation of Bone Marrow Mature Recirculating but Not Marginal Zone B Cells in Murine Models of Chronic Inflammation

Inflammation promotes granulopoiesis over B lymphopoiesis in the bone marrow (BM). We studied B cell homeostasis in two murine models of T cell mediated chronic inflammation, namely calreticulin-deficient fetal liver chimeras (FLC), which develop severe blepharitis and alopecia due to T cell hyper responsiveness, and inflammatory bowel disease (IBD) caused by injection of CD4+ naïve T cells into lymphopenic mice. We show herein that despite the severe depletion of B cell progenitors during chronic, peripheral T cell-mediated inflammation, the population of BM mature recirculating B cells is unaffected. These B cells are poised to differentiate to plasma cells in response to blood borne pathogens, in an analogous fashion to non-recirculating marginal zone (MZ) B cells in the spleen. MZ B cells nevertheless differentiate more efficiently to plasma cells upon polyclonal stimulation by Toll-like receptor (TLR) ligands, and are depleted during chronic T cell mediated inflammation in vivo. The preservation of mature B cells in the BM is associated with increased concentration of macrophage migration inhibitory factor (MIF) in serum and BM plasma. MIF produced by perivascular dendritic cells (DC) in the BM provides a crucial survival signal for recirculating B cells, and mice treated with a MIF inhibitor during inflammation showed significantly reduced mature B cells in the BM. These data indicate that MIF secretion by perivascular DC may promote the survival of the recirculating B cell pool to ensure responsiveness to blood borne microbes despite loss of the MZ B cell pool that accompanies depressed lymphopoiesis during inflammation.

Abnormalities of B cell subsets in patients with systemic lupus erythematosus

The prototypic autoimmune disease, SLE, is known to be associated with polyclonal B cell hyperreactivity. Developing an understanding of the complex nature of human B cell differentiation, largely through the application of multiparameter flow cytometry to an analysis of circulating B cells has permitted an assessment of whether specific stages of B cell maturation are affected by the tendency for polyclonal B cell activation. Moreover, the analysis of perturbations of the specific stages of B cell maturation has generated new information on whether abnormalities in B cell differentiation are primarily involved in autoimmune disease immunopathology or, rather, are secondary to the inflammatory environment characteristic of subjects with this autoimmune disease. Multivariant analysis has begun to document abnormalities in B cell maturation that are primarily associated with lupus, or, alternatively related to disease duration, disease activity and concomitant medication. Together, these analyses have provided new insights on the role of B cell over-reactivity in SLE.

Serum Amyloid A and C-Reactive Protein Concentrations Are Differently Associated with Markers of Autoimmunity in Patients with Primary Sjögren’s Syndrome

Primary Sjögren's syndrome (pSS) is an autoimmune disease in which the concentration of the acute-phase protein serum C-reactive protein (CRP) is low. We investigated whether levels of another acute-phase protein, serum amyloid A (SAA), are increased in patients with pSS and whether the immunological markers in patients with pSS are associated with variation in SAA levels. Serum SAA concentrations were measured by ELISA in 74 patients with pSS and in 56 control subjects with sicca symptoms. Median SAA levels did not differ significantly between patients with pSS and subjects with sicca symptoms. In patients with pSS SAA concentrations correlated significantly with age, leukocyte count, CRP, interleukin 6, and C4. Unlike CRP, there was a significant inverse correlation between SAA and serum IgG levels and anti-SSA antibody titers, as well as a trend towards an inverse correlation between SAA and antinuclear antibody and rheumatoid factor titers. Our data imply that high SAA production could constitute a protective element in pSS: high SAA levels inhibit in particular various signs of B cell hyperreactivity, i.e., IgG and autoantibody production.

Isoform-specific regulation of immune cell reactivity by the catalytic subunit of protein kinase A (PKA)

There are two major genes encoding the catalytic subunits of protein kinase A, Cα and Cβ. The functional significance of these isoforms is enigmatic. Lymphoid cells of the immune system express both Cα and Cβ. In this study we tested the role of Cα and Cβ in regulating immune cell reactivity to antigens using mice carrying a targeted disruption of the Cα and Cβ gene respectively. Cα and Cβ ablation both resulted in a 50% reduction in PKA-specific kinase activity and the level of PKA type I but not PKA type II. Moreover, despite that C subunit ablation did not affect immune cell development and homeostasis, Cα but not Cβ ablation augmented expression of the activation marker CD69 on lymphocytes. CD69 induction coincided with immune cell hyperresponsiveness and was associated with reduced sensitivity to cAMP-mediated inhibition of anti-CD3 induced T cell proliferation. Our results imply that Cα is required for normal immune cell reactivity and demonstrates isoform-specific effects and non-redundant functions of C subunit isoforms expressed in the same cell.

Short Communication:HIV Type 1 Viremia on ART Is Positively Associated with Polyclonal T Cell Proliferation in Subjects with T Cell IFN-γ Secretion Levels Comparable to Those of Uninfected Subjects

We investigated the association between plasma HIV-1 RNA, immune activation, and polyclonal T cell function in viremic subjects whether on or off antiretroviral therapy (ART). The surface expression of activation/functional molecules on T cells and monocytes as well as cytokine secretion and T cell proliferation were assessed in 23 HIV-1(-) and 79 HIV-1(+)-infected subjects with different levels of viral suppression and CD4(+) T cell count >250 cells/mm(3) for >6 months. Viral replication was associated with increased T cell and monocyte activation irrespective of ART. In subjects with a detectable viral load on ART, we found a positive association with anti-CD3/CD28-induced T cell proliferation compared to patients with undetectable viral load (<400 copies/ml). No difference among groups was observed for anti-CD3/CD28-mediated IFN-gamma responses. The presence of an unexpected positive association between polyclonal T cell proliferation and viral load in subjects with levels of T cell IFN-gamma responses comparable to those of uninfected subjects is of potential relevance to an increase in T cell activation response before the loss of polyclonal cytokine secretion and proliferation observed with disease progression. This finding suggests that T cell hyperresponsiveness may play a role in the pathogenesis of immune comorbidities on ART.

CD4+ T cell hyper-responsiveness in CD45 transgenic mice is independent of isoform

The CD45 tyrosine phosphatase is required for T cell development and function by virtue of its role as a positive regulator of src family kinase activity. In addition, recent data have highlighted that CD45 also acts as a negative regulator of Lck function by dephosphorylation of critical tyrosine residues. Lck functionality and TCR responsiveness are elevated in transgenic mice expressing the CD45RO isoform at 'intermediate' (10-40% of wild type) levels, indicating that the expression level of CD45 is critical in determining the sensitivity of T cells to TCR stimulation. However, it is unclear whether such a phenotype is specific for the CD45RO isoform, typically expressed by activated T cells. In the present work, the roles of three isoforms of CD45, RO, RB and RABC, in thymocyte development, T cell responses and TCR signalling pathways were directly compared. The data demonstrate that expression of CD45RB or CD45RABC at intermediate levels also results in CD4(+) T cell hyper-reactivity, as previously published for CD45RO. These data emphasize the dual functions of CD45 as both a positive and a negative regulators of TCR signalling irrespective of specific isoform expression.

Accumulation of splenic plasma cells in lyn−/− mice is dependent on Bruton's tyrosine kinase but not IL‐6

Deficiency of Lyn, a negative regulator of B and myeloid cell activation, results in B cell hyperresponsiveness, plasma cell accumulation, and production of autoantibodies in mice. Since accumulation of peripheral plasma cells is a common feature of both human and murine lupus, we have studied the mechanisms regulating this process in lyn−/− mice. Lyn‐deficient mice expressing reduced dosage of Btk (Btklo), a target of Lyn‐dependent inhibitory pathways, retain hypersensitivity to B cell receptor crosslinking but do not demonstrate increased plasma cell numbers or produce autoantibodies. Bone marrow‐derived macrophages from lyn−/− mice secrete more IL‐6, which promotes plasma cell differentiation and survival, than do wild type cells upon stimulation with LPS. Intracelluar staining for IL‐6 in splenic CD11b+ cells reveals that a greater frequency of lyn−/− myeloid cells produce IL‐6 upon LPS exposure than do wild type cells. Also, sera IL‐6 is significantly increased in aged lyn−/− mice. To determine if these effects are Btk‐mediated, we examined lyn−/−btklo mice and found that both production of IL‐6 in splenic CD11b+ cells and sera IL‐6 levels are normalized in lyn−/−btklo mice. However, lyn−/−IL‐6−/− mice continue to exhibit both plasma cell accumulation and production of anti‐DNA antibodies. Thus, plasma cell and autoimmune phenotypes in lyn−/− mice are mediated by Btk but not IL‐6.

Elevated serum decoy receptor 3 with enhanced T cell activation in systemic lupus erythematosus

Decoy receptor 3 (DcR3/TR6) is a decoy receptor for the Fas ligand (FasL) and can inhibit FasL-induced apoptosis. It has been reported recently that DcR3 can induce T cell activation via co-stimulation of T cells, suggesting that DcR3 may be involved in the pathophysiology of autoimmune diseases. This study aims to analyse the serum DcR3 in patients with systemic lupus erythematosus (SLE) and to investigate the role of DcR3 in the pathogenesis of SLE. Significantly elevated serum DcR3 was observed in SLE patients, and the mean serum DcR3 level was significantly higher for those with active disease [SLE disease activity index (SLEDAI) >/= 10] compared with that in patients with inactive disease (SLEDAI < 10). In addition to reducing activation-induced cell death in activated T cells via neutralization of the FasL, soluble DcR3-Fc enhanced T cell proliferation and increased interleukin-2 and interferon-gamma production via co-stimulation of T cells. Moreover, enhanced T cell reactivity to DcR3-induced co-stimulation was demonstrated in lymphocytes from patients with SLE, suggesting the elevated serum DcR3 may associate with enhanced T cell activation in vivo. These findings are the first to demonstrate that serum DcR3 concentrations are increased in SLE patients, and this may imply a possible role of DcR3 in the pathogenesis of SLE via enhanced T cell hyperreactivity and reduced apoptosis in activated T cells.

Calcium signaling in airway smooth muscle.

Contractility of airway smooth muscle requires elevation of intracellular calcium concentration. Under resting conditions, airway smooth muscle cells maintain a relatively low intracellular calcium concentration, and activation of the surface receptors by contractile agonists results in an elevation of intracellular calcium, culminating in contraction of the cell. The pattern of elevation of intracellular calcium brought about by agonists is a dynamic process and involves the coordinated activities of ion channels located in the plasma membrane and the sarcoplasmic reticulum. Among the signaling molecules involved in this dynamic calcium regulation in airway smooth muscle cells are inositol 1,4,5-trisphosphate and cyclic ADP-ribose, which mobilize calcium from the sarcoplasmic reticulum by acting via the inositol 1,4,5-trisphosphate and ryanodine receptors, respectively. In addition, calcium influx from the extracellular space is critical for the repletion of the intracellular calcium stores during activation of the cells by agonists. Calcium influx can occur via voltage- and receptor-gated channels in the plasma membrane, as well as by influx that is triggered by depletion of the intracellular stores (i.e., store-operated calcium entry mechanism). Transient receptor potential proteins appear to mediate the calcium influx via receptor- and store-operated channels. Recent studies have shown that proinflammatory cytokines regulate the expression and activity of the pathways involved in intracellular calcium regulation, thereby contributing to airway smooth muscle cell hyperresponsiveness. In this review, we will discuss the specific roles of cyclic ADP-ribose/ryanodine receptor channels and transient receptor potential channels in the regulation of intracellular calcium in airway smooth muscle cells.

Sjögren's Syndrome

Sjögren's syndrome (SS) is a chronic, slowly progressive, inflammatory, autoimmune disease characterized by (1) lymphocytic infiltration of the exocrine glands leading to diminished or absent glandular secretion, and (2) marked B-lymphocytic cell hyperreactivity manifested initially by a variety of serum autoantibodies, including those against the Ro(SSA) and La(SSB) ribonucleoproteins, ending in the development of B cell non-Hodgkin's lymphoma in a substantial number of patients. Most patients with SS present only with keratoconjunctivitis sicca and xerostomia. However, approximately 40% develop extraglandular manifestations that present in two ways: (1) the development of lymphoepithelial lesions in several extra-exocrine gland tissues (i.e., bronchi, renal tubules, or biliary ducts), and (2) vasculitis related to the deposition of immune complexes due to B cell hyperreactivity. Pulmonary manifestations develop in some patients and may present as (1) bronchitis sicca; (2) a wide spectrum of lymphoproliferative diseases, ranging from bronchus-associated lymphoid tissue (BALT) hyperplasia, lymphoid interstitial pneumonia, and B cell non-Hodgkin's lymphoma mainly of the extranodal marginal zone B-cell lymphoma of BALT-type or rarely of higher-grade malignancy; and (3) other interstitial pneumonias. Pleuritis can be seen in SS patients with associated systemic lupus erythematosus or rheumatoid arthritis.

Altered Expression of Fcγ and Complement Receptors on B Cells in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by B cell hyper-reactivity, autoantibody production, immune complex (IC) deposition, and multiple organ damage. The contribution of IC and B cell-mediated changes in the pathogenesis of SLE is well established, however, the exact role of IC-binding receptors expressed on B cells, Fcgamma receptors, and complement receptors CR1 and CR2 in these pathological processes is unclear. Development of lupus-like symptoms in mice defective for the inhibitory Fc-gammaRIIb and genetic association of certain FcgammaR genes with SLE demonstrate a significant role for these receptors but reports indicating alterations of Fcgamma or complement receptor-mediated B cell functions in human SLE are relatively few. The present review highlights a selected set of data including our own discussing the significance of animal models, genetics, and functional alterations of these IC-binding receptors in the etiopathogenesis of SLE.

Feedback Regulation of Murine Autoimmunity via Dominant Anti-Inflammatory Effects of Interferon γ

There is a paucity of knowledge concerning the immunologic sequelae that culminate in overt autoimmunity. In the present study, we have analyzed the factors that lead to disease in the model of autoimmunity, murine experimental autoimmune encephalomyelitis (EAE). EAE in H-2(u) mice involves autoreactive CD4(+) T cells that are induced by immunization with the immunodominant N-terminal epitope of myelin basic protein. The affinity of this epitope for I-A(u) can be increased by substituting lysine at position 4 with tyrosine, and this can be used to increase the effective Ag dose. Paradoxically, high doses of Ag are poorly encephalitogenic. We have used quantitative analyses to study autoreactive CD4(+) T cell responses following immunization of mice with Ag doses that are at the extremes of encephalitogenicity. A dose of autoantigen that is poorly encephalitogenic results in T cell hyperresponsiveness, triggering an anti-inflammatory feedback loop in which IFN-gamma plays a pivotal role. Our studies define a regulatory mechanism that serves to limit overly robust T cell responses. This feedback regulation has broad relevance to understanding the factors that determine T cell responsiveness.