Tumor necrosis factor-alpha and interferon-gamma synthesis by cerebrospinal fluid-derived T cell clones in multiple sclerosis

IFN-γ and TGF-β, Crucial Players in Immune Responses: A Tribute to Howard Young

Interferon gamma (IFN-γ) and transforming growth factor beta (TGF-β), both pleiotropic cytokines, have been long studied and described as critical mediators of the immune response, notably in T cells. One of the investigators who made seminal and critical discoveries in the field of IFN-γ biology is Dr. Howard Young. In this review, we provide an overview of the biology of IFN-γ as well as its role in cancer and autoimmunity with an emphasis on Dr. Young's critical work in the field. We also describe how Dr. Young's work influenced our own research studying the role of TGF-β in the modulation of immune responses.

Interferon gamma in autoimmunity: A complicated player on a complex stage

Early views of autoimmune disease cast IFNγ as a prototypic pro-inflammatory factor. It is now clear that IFNγ is capable of both pro- and anti-inflammatory activities with the functional outcome dependent on the physiological and pathological setting examined. Here, the major immune modulatory activities of IFNγ are reviewed and current evidence for the impact of IFNγ on pathology and regulation of several autoimmune diseases and disease models is summarized.

Natalizumab exerts direct signaling capacity and supports a pro-inflammatory phenotype in some patients with multiple sclerosis

Natalizumab is a recombinant monoclonal antibody raised against integrin alpha-4 (CD49d). It is approved for the treatment of patients with multiple sclerosis (MS), a chronic inflammatory autoimmune disease of the CNS. While having shown high therapeutic efficacy, treatment by natalizumab has been linked to progressive multifocal leukoencephalopathy (PML) as a serious adverse effect. Furthermore, drug cessation sometimes induces rebound disease activity of unknown etiology. Here we investigated whether binding of this adhesion-blocking antibody to T lymphocytes could modulate their phenotype by direct induction of intracellular signaling events. Primary CD4⁺ T lymphocytes either from healthy donors and treated with natalizumab in vitro or from MS patients receiving their very first dose of natalizumab were analyzed. Natalizumab induced a mild upregulation of IL-2, IFN-γ and IL-17 expression in activated primary human CD4⁺ T cells propagated ex vivo from healthy donors, consistent with a pro-inflammatory costimulatory effect on lymphokine expression. Along with this, natalizumab binding triggered rapid MAPK/ERK phosphorylation. Furthermore, it decreased CD49d surface expression on effector cells within a few hours. Sustained CD49d downregulation could be attributed to integrin internalization and degradation. Importantly, also CD4⁺ T cells from some MS patients receiving their very first dose of natalizumab produced more IL-2, IFN-γ and IL-17 already 24 h after infusion. Together these data indicate that in addition to its adhesion-blocking mode of action natalizumab possesses mild direct signaling capacities, which can support a pro-inflammatory phenotype of peripheral blood T lymphocytes. This might explain why a rebound of disease activity or IRIS is observed in some MS patients after natalizumab cessation.

Th17 cells in autoimmune demyelinating disease

Recently published studies in multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE) have demonstrated an association between the development of demyelinating plaques and the accumulation of Th17 cells in the central nervous system and periphery. However, a causal relationship has been difficult to establish. In fact, in reports published thus far, interleukin (IL)-17A deficiency or neutralization in vivo attenuates, but does not completely abrogate, EAE. There is growing evidence that clinically similar forms of autoimmune demyelinating disease can be driven by myelin-specific T cells of distinct lineages with different degrees of dependence on IL-17A production to achieve their pathological effects. While such observations cast doubts about the potential therapeutic efficacy of Th17 blocking agents in MS, the collective data suggest that IL-17A expression in peripheral blood mononuclear cells could serve as a surrogate biomarker of neuroinflammation and plaque formation and be a useful outcome measure for future clinical trials.

Innate immune response induced by Theiler's murine encephalomyelitis virus infection

Although the causative agents of human multiple sclerosis (MS) are not known, it is suspected that a viral infection may be associated with the initiation of the disease. Several viral disease models in mice have been studied to understand the pathogenesis of demeylination. In particular, Theiler's murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD) has been extensively studied as a relevant model. Various cytokines and chemokines are produced upon viral infection by different cell types, including antigen-presenting cells (APCs) such as macrophages; dendritic cells (DCs); and glial cells, such as astrocytes, microglia, and oligoden-drocytes. The upregulation of the corresponding molecules are also found in MS and are likely to play an important role in the protection and/or pathogenesis of chronic inflammatory demyelinating disease. In this review, the type of cells and molecules, gene-activation mechanisms as well as their potential roles in protection and pathogenesis will be discussed.

CXC chemokine receptors on human oligodendrocytes: implications for multiple sclerosis

Subsequent to demyelination in multiple sclerosis, myelin repair occurs but, as lesions age, the ability to remyelinate diminishes. Molecular pathways underlying oligodendrocyte behaviour during CNS remyelination remain to be elucidated. In this study, we report for the first time constitutive expression of the CXC/alpha chemokine receptors, CXCR1, CXCR2 and CXCR3, on oligodendrocytes in normal adult human CNS tissue, the levels of which were upregulated in multiple sclerosis and other neurological diseases (OND). In addition, both immature (A2B5+/O4+) and more mature (CNPase+) human oligodendrocytes in vitro expressed the same three receptors. The respective ligands to CXCR1, CXCR2 and CXCR3 [i.e. CXCL8/IL-8, CXCL1/GRO-alpha and CXCL10/IP-10), were absent in CNS tissue from normals and subjects with OND, but were present at high levels on hypertrophic (reactive) astrocytes at the edge of active (but not silent) multiple sclerosis lesions. Astrocytes in vitro could be induced to express chemokines following stimulation with pro-inflammatory cytokines. CXCL8 and CXCL1 production by human astrocytes at both the RNA and protein levels could be induced by interleukin (IL)-1beta, while CXCL10 was induced by both IL-1beta and interferon-gamma. Since these cytokines are integral to inflammatory events occurring at the margins of active multiple sclerosis lesions, their upregulation in these regions may underlie the dynamics of chemokine expression observed herein. The simultaneous expression of different CXC chemokine receptors on oligodendrocytes, and their ligands on astrocytes around multiple sclerosis lesions, may bespeak novel functional roles for these immune system molecules in the recruitment of oligodendrocytes and remyelination.

The human T cell response to myelin oligodendrocyte glycoprotein: a multiple sclerosis family-based study

Myelin oligodendrocyte glycoprotein (MOG) is an encephalitogenic myelin protein and a likely autoantigen in human multiple sclerosis (MS). In this work, we describe the fine specificity and cytokine profile of T cell clones (TCC) directed against MOG in three nuclear families, comprised of four individuals affected with MS and their HLA-identical siblings. TCC were generated from PBMC by limiting dilution against a mixture of eleven 20-mer overlapping peptides corresponding to the encephalitogenic extracellular domain of human MOG (aa 1-120). The frequency of MOG peptide-reactive T cells was surprisingly high (range, 1:400 to 1:3,000) and, unexpectedly, cloning efficiencies were highest at low seeding densities of 10(2) or 10(3) PBMC per well. A total of 235 MOG peptide-reactive TCC were produced, all of which were CD4(+)CD8(-)TCRalphabeta(+)TCRgammadelta(-). All 11 MOG peptides were recognized by the TCC, and different epitopes of MOG appeared to be immunodominant in the HLA-identical siblings. The patterns of cytokine secretion by TCC from single individuals were generally similar. The healthy individuals exhibited Th2-, Th0-, and T regulatory cell 1-like cytokine profiles, whereas TCC from one sibling with MS had a striking Th1-like phenotype, producing high levels of IFN-gamma and TNF-alpha, and low IL-4 levels. Thus, MOG-reactive T cells appear to constitute an important part of the natural T cell repertoire, a finding that could contribute to the development of autoimmunity to this protein.

CD40 engagement stimulates IL-12 p70 production by human microglial cells: basis for Th1 polarization in the CNS

The APC-derived cytokine interleukin (IL)-12 polarizes CD4 T cells towards the pro-inflammatory Th1 phenotype and has been shown to be crucial for the development of EAE in rodents. In this study we demonstrate that production of IL-12 by human adult CNS-derived microglial cells can be triggered by cell contact with activated T cells. Microglial activation and IL-12 production can be blocked by anti-CD154 mAbs. IL-12 production could also be induced by direct engagement of CD40 on microglia using a CD40 agonist. IL-12 secretion by microglia is significantly reduced by TNF and IFN-gamma antagonists showing that the IL-12 production is subject to regulation by auto- and paracrine stimuli.

Ingested IFN-alpha has biological effects in humans with relapsing-remitting multiple sclerosis

Parenterally administered human recombinant type I interferons (hrIFN) in relapsing-remitting multiple sclerosis (RRMS) decrease relapses and spontaneous in vitro IFN-gamma production, reduce clinical progression, and decrease magnetic resonance imaging (MRI)-defined disease activity and lesions. Parenterally administered type I IFN use is limited by clinical and chemical toxicities, and the induction of antibodies that abrogate their activity in vivo correlated with the loss of clinical benefit. Therefore, we determined whether ingested IFN-alpha was non-toxic and had biological effects in humans. Ingested hrIFN-alpha showed no toxicity in normal volunteers or patients with RRMS at doses ranging from 300 to 100,000 units. In subjects with RRMS, a significant decrease in Con A-mediated proliferation and serum soluble intercellular adhesion molecule-1 (sICAM-1), a surrogate measure for disease activity in MS, was found after ingesting 10,000 and 30,000 units IFN-alpha The RRMS subjects also showed decreased IL-2 secretion after ingesting 10,000 units IFN-alpha and decreased IFN-gamma, TGF-beta and IL-10 production after ingesting 30,000 units IFN-alpha. The decreased secretion of IFN-gamma and IL-2 by ingested IFN-alpha suggests that oral IFN-alpha may cause a functional inhibition of Th J-like T helper cells in RRMS, a potential site of intervention at the level of effector T cells in MS. Our studies support the oral use of human IFN-alpha as a biological response modifier in humans.

Type 1 and type 2 cytokine dysregulation in human infectious, neoplastic, and inflammatory diseases

In the mid-1980s, Mosmann, Coffman, and their colleagues discovered that murine CD4+ helper T-cell clones could be distinguished by the cytokines they synthesized. The isolation of human Th1 and Th2 clones by Romagnani and coworkers in the early 1990s has led to a large number of reports on the effects of Th1 and Th2 on the human immune system. More recently, cells other than CD4+ T cells, including CD8+ T cells, monocytes, NK cells, B cells, eosinophils, mast cells, basophils, and other cells, have been shown to be capable of producing "Th1" and "Th2" cytokines. In this review, we examine the literature on human diseases, using the nomenclature of type 1 (Th1-like) and type 2 (Th2-like) cytokines, which includes all cell types producing these cytokines rather than only CD4+ T cells. Type 1 cytokines include interleukin-2 (IL-2), gamma interferon, IL-12 and tumor necrosis factor beta, while type 2 cytokines include IL-4, IL-5, IL-6, IL-10, and IL-13. In general, type 1 cytokines favor the development of a strong cellular immune response whereas type 2 cytokines favor a strong humoral immune response. Some of these type 1 and type 2 cytokines are cross-regulatory. For example, gamma interferon and IL-12 decrease the levels of type 2 cytokines whereas IL-4 and IL-10 decrease the levels of type 1 cytokines. We use this cytokine perspective to examine human diseases including infections due to viruses, bacteria, parasites, and fungi, as well as selected neoplastic, atopic, rheumatologic, autoimmune, and idiopathic-inflammatory conditions. Clinically, type 1 cytokine-predominant responses should be suspected in any delayed-type hypersensitivity-like granulomatous reactions and in infections with intracellular pathogens, whereas conditions involving hypergammaglobulinemia, increased immunoglobulin E levels, and/or eosinophilia are suggestive of type 2 cytokine-predominant conditions. If this immunologic concept is relevant to human diseases, the potential exists for novel cytokine-based therapies and novel cytokine-directed preventive vaccines for such diseases.

No genetic linkage between multiple sclerosis and the interferon alpha/beta locus

Multiple sclerosis (MS) is probably caused by an interaction of genetic and environmental factors. The genetic component is reflected by a ten-fold higher concordance rate in monozygotic (27%) compared to dizygotic (3%) twin pairs. Treatment with interferon was recently reported to have a favorable effect in patients with relapsing-remitting MS. In the present familial study, we have investigated the possibility of a genetic association between the highly polymorphic Interferon alpha beta locus and the development of MS. Based on our data, we conclude that there is no linkage between the Interferon alpha beta locus and MS.

Presence of tumor necrosis factor alpha and interleukin-6 in renal mesangial cells of lupus nephritis patients

Tumor necrosis factor alpha (TNF alpha) and interleukin-6 (IL-6) antigenic sites were shown within the resident glomerular mesangial cells of lupus nephritis patients applying the colloidal gold immunocytochemical approach at the electron microscopic level. Using specific polyclonal antibodies against human recombinant (hr) TNF alpha and hrIL-6 in conjunction with the protein A-gold complex, TNF alpha and IL-6 were shown in the mesangial cells, being particularly associated with the membranes of the rough endoplasmic reticulum. In addition, IL-6 also was present in glomerular immune deposits and occasionally in glomerular epithelial cells. In normal renal tissue the TNF alpha and IL-6 immunoreactivities were undetectable. The specific presence of TNF alpha and IL-6 in pathological specimens was shown by several control experiments. Thus, our results offered morphological support that TNF alpha and IL-6 might play a role in human lupus nephritis. The data showed their synthesis by the mesangial cells and their possible participation in the progression to chronicity of the renal injury on secretion.

The role of genetic factors in multiple sclerosis susceptibility

There has been increasing evidence that genetic factors have a role in determining susceptibility to MS. Re-examination of results from prevalence and migration surveys reveals that there remains considerable ambiguity in interpretation. Some patterns previously thought to decisively support environmental determination may still be explained, at least in part, on a genetic basis. It seems inescapable that MS is probably due to an interaction of genetic and environmental factors. It remains undetermined whether or not genes exist which are truly necessary for the development of the disease. Existing data are consistent with the notion that the study of MS susceptibility will parallel the findings in experimental models of spontaneous autoimmunity and that at very least, two genes and almost certainly several genes will be found to influence susceptibility and interact in as yet unknown ways. One of these loci appears to be the Class II MHC, although its role may be minor at the germ line level. Roles for the T-cell receptor alpha and beta loci appear to be minor and may even be non-existent in contributing to heritable susceptibility. We predict that additional loci will be identified which influence both susceptibility and outcome and will be more important. Furthermore, it is clear that the understanding of the contribution of individual susceptibility loci will continue to be difficult because of the constraints of human pedigree data. It is likely that further resolution of the questions posed above related to genetic susceptibility in MS will require multicenter collaboration.

Acetylcholine receptor-reactive T cells in myasthenia gravis: evidence for the involvement of different subpopulations of T helper cells

Patients with myasthenia gravis have a high prevalence of acetylcholine receptor-specific T lymphocytes in the peripheral blood. Our earlier study shows that these T lymphocytes are stimulated to secrete interferon (IFN)-gamma and interleukin (IL)-2 in response to the autoantigen. Such stimulated T cells may be subdivided into different subsets according to the pattern of cytokine production. In the present study we have investigated the subpopulations of cells by analyzing their IL-4, IFN-gamma and IL-2 secretion pattern. Autoantigen-stimulated IL-4 secretion was found in 55% of the patients, IFN-gamma secretion in 86% and IL-2 secretion in 72%. T lymphocytes from all patients who responded with increased IL-2 secretion also showed increased IFN-gamma secretion. Stimulated IL-4 secretion was detected both in the presence and absence of stimulated IFN-gamma secretion. Depletion of monocytes/macrophages from peripheral blood mononuclear cell preparation and treatment of the cells with a mouse anti-human HLA-DR antibody abolished the secretion of IFN-gamma and IL-4. There were positive correlations between the numbers of IFN-gamma- and IL-2-secreting T cells and the numbers of B cells secreting antibodies against the acetylcholine receptor. Our results show that acetylcholine receptor-stimulated T lymphocytes secrete IL-4, IFN-gamma and/or IL-2. This T cell response is major histocompatibility complex (MHC) class II-restricted and monocyte/macrophage-dependent. Our study indicates that both Th1/Th2 or Th0 subpopulations of the T lymphocytes are involved in the autoimmune response in myasthenia gravis.

Cytokine-regulated proteases in autoimmune diseases

Progress in the research of cellular and humoral immunity has been exponential during the past decade, although it is still insufficient to explain fully the pathogenesis of autoimmunity. Over the same period, an understanding of the cytokine network and the extracellular proteolysis cascades has grown considerably. Here, Ghislain Opdenakker and Jo Van Damme propose the REGA-model (Remnant Epitope Generates Autoimmunity) to explain the generation of autoantigens and their interaction with the T-cell receptor complex. Although this model may be applied to all known autoimmune diseases, multiple sclerosis has been used as the specific example here.

Elevated serum levels of tumor necrosis factor-alpha in Guillain-Barré syndrome

Activated T lymphocytes and macrophages play a putative role in the the pathogenesis of Guillain-Barré syndrome. Both cell types secrete tumor necrosis factor-alpha, a cytokine that has well-recognized toxic effects on myelin, Schwann cells, and endothelial cells. We determined serum and cerebrospinal fluid concentrations of tumor necrosis factor alpha in 26 patients with Guillain-Barré syndrome, 27 patients with other polyneuropathies, 30 patients with neurological diseases of the central nervous system, and 14 healthy control subjects. Markedly increased serum levels were detected in 14 patients (54%) with Guillain-Barré syndrome and to a significantly lesser extent, in patients with other polyneuropathies (26%) and in neurological control subjects (23%). Tumor necrosis factor-alpha was not detected in the cerebrospinal fluid of patients with Guillain-Barré syndrome or other polyneuropathies. Increased serum concentrations in patients with Guillain-Barré syndrome correlated directly with disease severity and these concentrations returned to normal in parallel with clinical recovery. These findings emphasize the complexity of the immune response in patients with Guillain-Barré syndrome and suggest that tumor necrosis factor-alpha may be important in the pathogenesis of peripheral demyelination in this disorder.