Constitutive production of NF-kappaB2 p52 is not tumorigenic but predisposes mice to inflammatory autoimmune disease by repressing Bim expression

Normal development of the immune system requires regulated processing of NF-kappaB2 p100 to p52, which activates NF-kappaB2 signaling. Constitutive production of p52 has been suggested as a major mechanism underlying lymphomagenesis induced by NF-kappaB2 mutations, which occur recurrently in a variety of human lymphoid malignancies. To test the hypothesis, we generated transgenic mice with targeted expression of p52 in lymphocytes. In contrast to their counterparts expressing the tumor-derived NF-kappaB2 mutant p80HT, which develop predominantly B cell tumors, p52 transgenic mice are not prone to lymphomagenesis. However, they are predisposed to inflammatory autoimmune disease characterized by multiorgan infiltration of activated lymphocytes, high levels of autoantibodies in the serum, and immune complex glomerulonephritis. p52, but not p80HT, represses Bim expression, leading to defects in apoptotic processes critical for elimination of autoreactive lymphocytes and control of immune response. These findings reveal distinct signaling pathways for actions of NF-kappaB2 mutants and p52 and suggest a causal role for sustained NF-kappaB2 activation in the pathogenesis of autoimmunity.     

Graves' ophthalmopathy.

Graves'' ophthalmopathy usually occurs in association with hyperthyroidism. Its occasional occurrence in the absence of thyroid disease suggests, however, that it may be a separate autoimmune disorder. While the evidence supporting an autoimmune pathogenesis is considerable for the ophthalmopathy, it is not so impressive as that for Graves'' hyperthyroidism: orbital antibodies have not been convincingly demonstrated and autoantigens have not been identified. On the other hand, in patients with Graves'' ophthalmopathy the orbital tissues and eye muscle membranes are infiltrated with lymphoid cells and show evidence of cell-mediated immune reactions. Although there is some evidence that binding of thyroid stimulating hormone fragments and thyroglobulin-antithyroglobulin immune complexes to eye muscle membranes may be important in the pathogenesis of the ophthalmopathy, this needs to be confirmed. The mechanism for the association of hyperthyroidism and ophthalmopathy is unknown, but the association likely reflects an influence of thyroid hormones on the immune system. In view of the autoimmune pathogenesis the logical treatment of Graves'' ophthalmopathy appears to be immunosuppression.     

Alternative pathways of NF-kappaB activation: a double-edged sword in health and disease

While the classical pathway of NF-kappaB activation plays critical roles in a wide range of biological processes, the more recently described "non-canonical" NF-kappaB pathway has important but more restricted roles in both normal and pathological processes. The non-canonical NF-kappaB pathway, based on processing of the nf-kappab2 gene product p100 to generate p52, appears to be involved in B-cell maturation and lymphoid development. Deregulated activation of this pathway has been observed in a variety of malignant and autoimmune diseases, thus inhibitors that specifically target p100 processing might be predicted to have potential roles as immunomodulators and in the therapy of malignant diseases. We review current understandings of NF-kappaB activation, particularly the mechanisms of p100 processing under both physiological and pathological conditions.     

Mechanism of Resistance to Steroids: Glucocorticoid Receptor Defect in Lymphoma Cells

GLUCOCORTICOIDS cause cytolysis of normal and neoplastic lymphoid cells^1,2—a reaction which is one basis for the use of these compounds in the therapy of neoplastic, autoimmune and other diseases of the lymphoid system. Unfortunately, resistance to steroids often develops during treatment, rendering the hormones therapeutically ineffective.     

Modulation of gene expression in autoimmune disease and aging by food restriction and dietary lipids

Several recent observations carried out by many investigators have offered some clues in understanding the mechanism of how food restriction (FR) acts in the prolongation of life-span, but the precise mechanisms involved in modulating the immune system have not been clearly understood. Our own ongoing studies indicate that FR may act at the molecular level and may extend the life-span by modulating functional activities of several genes in various target tissues. For instance, while cytochrome P-450 IIB1 and IIB2 expression is known to decline with age in ad libitum-fed rats, FR prevented the loss of (drug-inducible) P-450 enzymes in liver tissues. In addition, both alpha 2u-globulin and senescence marker protein 2 expressions, which are regulated by hormones, were also modulated during aging by FR in Fischer 344 male rats. In short-lived autoimmune-prone mice, both FR and omega-3 (n-3) fatty acids diet lowered the severity of autoimmune disease both in lupus-prone (NZB x NZW)F1 mice and in mice prone to develop lymphoproliferative and renal diseases, whereas saturated (n-9) and polyunsaturated (n-6) dietary lipids not only exacerbated autoimmune disease, but also significantly enhanced expression of several oncogenes in lymphoid tissues. FR and omega-3 fatty acids decreased the expression of certain oncogenes. Both FR and omega-3 fatty acids may modulate the aging and autoimmune disease processes by not only altering the fatty acid composition, membrane fluidity, and signal transduction, but also by modulating the lymphokine hormone receptors and their functions and thereby modulating expression of several genes in various tissues during the aging process.     

Chemokines determine local lymphoneogenesis and a reduction of circulating CXCR4+ T and CCR7 B and T lymphocytes in thyroid autoimmune diseases

Chemokines and their corresponding receptors are crucial for the recruitment of lymphocytes into the lymphoid organs and for its organization acting in a multistep process. Tissues affected by autoimmune disease often contain ectopic lymphoid follicles which, in the case of autoimmune thyroid disorders, are highly active and specific for thyroid Ags although its pathogenic role remains unclear. To understand the genesis of these lymphoid follicles, the expression of relevant cytokines and chemokines was assessed by real time PCR, immunohistochemistry and by in vitro assays in autoimmune and nonautoimmune thyroid glands. Lymphotoxin alpha, lymphotoxin beta, C-C chemokine ligand (CCL) 21, CXC chemokine ligand (CXCL) 12, CXCL13, and CCL22 were increased in thyroids from autoimmune patients, whereas CXCL12, CXCL13, and CCL22 levels were significantly higher in autoimmune glands with ectopic secondary lymphoid follicles than in those without follicles. Interestingly, thyroid epithelium produced CXCL12 in response to proinflammatory cytokines providing a possible clue for the understanding of how tissue stress may lead to ectopic follicle formation. The finding of a correlation between chemokines and thyroid autoantibodies further suggests that intrathyroidal germinal centers play a significant role in the autoimmune response. Unexpectedly, the percentage of circulating CXCR4(+) T cells and CCR7(+) B and T cells (but not of CXCR5) was significantly reduced in PBMCs of patients with autoimmune thyroid disease when they were compared with their intrathyroidal lymphocytes. This systemic effect of active intrathyroidal lymphoid tissue emerges as a possible new marker of thyroid autoimmune disease activity.     

Distinct pathways for NF-kappa B regulation are associated with aberrant macrophage IL-12 production in lupus- and diabetes-prone mouse strains

One characteristic of mice prone to a variety of autoimmune diseases is the aberrant regulation of cytokine production by macrophages (Mphi), noted in cells isolated well before the onset of disease. Strikingly, the pattern of IL-12 dysregulation, in particular, is consistent with the nature of the autoimmune disease that will develop in each strain, i.e., elevated in mice prone to Th1-mediated organ-specific disease (nonobese diabetic (NOD) and SJL mice) and reduced in lupus-prone strains (MRL/+ and NZB/W). Mechanistically, the abnormal regulation of IL-12 in these strains was found to be strictly associated with novel patterns of Rel binding in vitro to the unique NF-kappaB site in the IL-12 p40 promoter. In this study, we report several new findings related to these Rel-kappaB interactions. Evaluation of the p40 NF-kappaB site in vivo, assessed by chromatin immunoprecipitation, revealed Rel usage patterns similar to those found in vitro using EMSA, with preferential association of the p40 kappaB site with c-Rel in NOD Mphi but with p50 in NZB/W Mphi. Moreover, blocking c-Rel in primary Mphi, using short interfering RNA, selectively blocked IL-12 production and normalized the minimal, residual IL-12 levels. Nuclear extracts from NOD Mphi were characterized by c-Rel hyperphosphorylation, and dephosphorylation of nuclear proteins completely blocked binding to the kappaB site. In contrast, elevated IkappaB appears to be a likely mechanism accounting for the reduced nuclear c-Rel levels noted in NZB/W Mphi. Alterations in NF-kappaB metabolism thus appear to define a pathway regulating intrinsic IL-12 defects in both diabetes- and lupus-prone strains.     

Nuclear RelB+ cells are found in normal lymphoid organs and in peripheral tissue in the context of inflammation, but not under normal resting conditions

Differentiated dendritic cells (DC) have been identified by the presence of nuclear RelB (nRelB) and HLA-DR, and the absence of CD20 or high levels of CD68, in lymph nodes and active rheumatoid arthritis synovial tissue. The current studies aimed to identify conditions in which nRelB is expressed in human tissues, by single and double immunohistochemistry of formalin-fixed peripheral and lymphoid tissue. Normal peripheral tissue did not contain nRelB+ cells. nRelB+ DC were located only in T- or B-cell areas of lymphoid tissue associated with normal organs or peripheral tissues, including tonsil, colon, spleen and thymus, or in association with T cells in inflamed peripheral tissue. Inflamed sites included skin delayed-type hypersensitivity reaction, and a wide range of tissues affected by autoimmune disease. Nuclear RelB+-HLA-DR- follicular DC were located in B-cell follicles in lymphoid organs and in lymphoid-like follicles of some tissues affected by autoimmune disease. Lymphoid tissue T-cell areas also contained nRelB(-)-HLA-DR+ cells,some of which expressed CD123 and/or CD68. Nuclear RelB+ cells are found in normal lymphoid organs and in peripheral tissue in the context of inflammation, but not under normal resting conditions.     

Molecular mechanisms of the effect of herpesvirus saimiri protein StpC on the signaling pathway leading to NF-kappaB activation

Herpesvirus saimiri (Saimiriine herpesvirus-2) causes lethal T lymphoproliferative diseases in the susceptible species and transforms T lymphocytes to continuous growth in vitro. H. saimiri-induced transformation of T cells is becoming an important experimental tool of biomedical research. Two proteins of H. saimiri subgroup C, Tip and StpC, are essential for T cell transformation by this virus. It has been shown previously that StpC transforms fibroblasts, activates NF-kappaB, and binds to tumor necrosis factor (TNF)-receptor-associated factor (TRAF) proteins, but the molecular mechanism of its action remains insufficiently understood. This study further characterized the effect of StpC on NF-kappaB. First, StpC activates NF-kappaB via the consensus pathway involving activation of I-kappaB kinase and subsequent phosphorylation and degradation of I-kappaB in both T lymphoid and epithelial cells. Second, triggering of this pathway by StpC in both T lymphoid and epithelial cells is dependent on the presence of functional NF-kappaB-inducing kinase (NIK). Third, StpC physically interacts with TRAF in epithelial cells, and the effect of StpC on NF-kappaB activity in these cells requires the presence of functional TRAF. Finally the effect of StpC is completely independent of TNF-alpha, a well described stimulus of NF-kappaB activity. Moreover it appears that StpC uncouples stimulation of NF-kappaB activity from TNF-alpha stimulation. Overall these results argue that the effect of StpC on NF-kappaB is similar to the effects of other viral proteins, "usurping" the TRAF/NIK/I-kappaB kinase pathway, and reinforce the notion that the role of StpC in cell transformation by H. saimiri may be mediated by signaling that results in NF-kappaB activation.     

Guarding the immune system: suppression of autoimmunity by CD4+CD25+ immunoregulatory T cells

CD4+CD25+Foxp3+ T cells (CD25+ T regulatory [Treg] cells) are a naturally occurring suppressor T-cell population that regulates a wide variety of immune responses. A major function of CD25+ Treg cells is to inhibit the activity of self-reactive T cells that can potentially cause autoimmune disease. This review examines the recent advances in CD25+ Treg cell biology, with particular focus on the thymic and peripheral development of CD25+ Treg cells, the signals that promote their expansion and maintenance in the periphery and the mechanism by which they mediate their suppressor activity in peripheral lymphoid tissues. An understanding of these issues is likely to facilitate the development of CD25+ Treg-cell-based therapies for the treatment of autoimmune disease.     

Estrogen regulates the IFN-gamma promoter

The greater immune reactivity of females has been attributed in part to the influence of sex steroid hormones, but the underlying mechanisms are unknown. Here we report evidence that expression of the IFN-gamma gene may be subject to direct hormonal control. In a transient expression assay, the sex steroid 17 beta-estradiol markedly increases activity of the IFN-gamma promoter in lymphoid cells that express the appropriate hormone receptor. This effect is mediated by sequences in the 5'-flanking region of the gene, and can augment the effect of T cell-activating agents. Short term exposure to estradiol also increases IFN-gamma mRNA expression in Con A-treated murine spleen cells. Hormonal regulation of this pleiotropic cytokine may account in part for the ability of estrogen to potentiate many types of immune responses, and for the disproportionate susceptibility of females to autoimmune disease.     

Caspase recruitment domain (CARD)-dependent cytoplasmic filaments mediate bcl10-induced NF-kappaB activation

Mucosa-associated lymphoid tissue (MALT) lymphomas are associated with overexpression and constitutive activity of bcl10, a caspase recruitment domain (CARD)-containing protein that activates NF-kappaB. Here, we show that arrangement of overexpressed bcl10 protein in cytoplasmic filaments is essential for recruitment of signal transducer molecules-involved NF-kappaB activation. We also show that cytoskeleton elements regulate bcl10 signaling.Thus, organized assemblage of proteins in ordered structures linked to the cytoskeleton network may represent a general mechanism for intracellular signaling.     

Lymphotoxin/light,lymphoid microenvironments and autoimmune disease

Much of the efficiency of the immune system is attributed to the high degree of spatial and temporal organization in the secondary lymphoid organs. Signalling through the lymphotoxin (LT) pathway is a crucial element in the maintenance of this organized microenvironment. The effect of altering lymphoid microenvironments on immune responses remains relatively unexplored. Inhibitors of the LT and LIGHT pathways have been shown to reduce disease in a wide range of autoimmune models. This approach has provided a tool to probe the effect of manipulation of the microenvironment on both normal and pathological immune responses.     

Pathogenic and protective functions of TNF in neuroinflammation are defined by its expression in T lymphocytes and myeloid cells

TNF displays pathogenic activities in many autoimmune disorders. However, anti-TNF therapy in multiple sclerosis patients failed because of poorly understood reasons. We used a panel of gene-targeted mice that allowed cell-type specific ablation of TNF to uncover pathogenic and protective contributions of this cytokine during autoimmune disease of the CNS. T cells and myeloid cells were found to be critical cellular sources of TNF during experimental autoimmune encephalomyelitis (EAE). TNF produced by myeloid cells accelerated the onset of disease by regulation of chemokine expression in the CNS, driving the recruitment of inflammatory cells into the target organ. TNF produced by T cells exacerbated the damage to the CNS during EAE by regulating infiltration of inflammatory myeloid cells into the CNS. In secondary lymphoid organs, TNF expressed by myeloid cells and T cells acted in synergy to dampen IL-12p40 and IL-6 production by APCs, subsequently inhibiting the development of encephalitogenic T cell responses of Th1 and Th17 types. This dual role of TNF during EAE (protective in lymphoid organs and pathogenic in CNS) suggests that global TNF blockade might be inefficient in multiple sclerosis patients because augmented autoreactive T cell development in lymphoid tissues might overwhelm the beneficial effects resulting from TNF inhibition in the CNS.