The role of tumor necrosis factor and lymphotoxin in lymphoid organ development

High levels of Lymphotoxin-Beta (LT-Beta) gene expression in rheumatoid arthritis synovium: clinical and cytokine correlations

Lymphotoxin-Beta (LT-Beta) is implicated in lymphoid follicle development, production of pro-inflammatory cytokines, and can enhance the proliferation of fibroblasts and synoviocytes. The objective of this study was to investigate LT-Beta and LT-BetaReceptor (LT-BetaR) gene expression in RA patient synovium and blood samples compared with control individuals, and correlate with LT-Alpha and TNF-Alpha gene expression and disease parameters. RT-PCR was used to investigate the gene expression of LT-Beta, LT-BetaR, TNF-Alpha and LT-Alpha in the blood and synovium of RA patients and a control group of individuals. LT-Beta gene expression was significantly higher in RA patient synovium compared to control synovium (P = 0.005). There was a significant positive correlation between LT-Beta and LT-Alpha gene expression in both the synovium (P = 0.001) and blood (P = 0.002) of RA patients. LT-Beta gene expression was significantly higher in RA patient synovial samples that were inflamed to a moderately severe degree compared to those inflamed to a minimal degree (P = 0.02). Analysis of clinical variables revealed a significant positive correlation between LT-BetaR gene expression in RA patient synovium and Pain VAS Score (P = 0.01) and also HAQ Score (P = 0.01). Increased LT-Beta gene expression occurs in RA synovium and correlates with the degree of inflammation. LT-Beta may play a role in RA disease pathogenesis by contributing to a more intense inflammatory reaction in the synovium.

Lymphtoxin beta receptor-Ig protects from T-cell-mediated liver injury in mice through blocking LIGHT/HVEM signaling

LIGHT is a member of the TNF superfamily, which is transiently expressed on the surface of activated T lymphocytes and immature dendritic cells. Its known receptors are herpesvirus entry mediator (HVEM) prominently in T lymphocytes, and lymphtoxin beta receptor (LTbetaR) in stromal cells or nonlymphoid hematopoietic cells. Previous studies have shown that overexpression of LIGHT on T cells could lead to autoimmune reaction including lymphocytes activation, inflammation, and tissue destruction. To address the role of LIGHT/HVEM signaling in autoimmune hepatitis, an experimental colitis model induced by intravenous administration of concanavalin A (ConA) was given a soluble LTbetaR-Ig fusion protein as a competitive inhibitor of LIGHT/HVEM pathway. Marked elevation of LIGHT expression was detected in isolate intrahepatic leukocytes (IHLs) of the experimental animal. Treatment with LTbetaR-Ig significantly attenuated the progression and histological manifestations of the hepatic inflammation and reduced the production of inflammatory cytokines including TNF-alpha, IFN-gamma. Moreover, LTbetaR-Ig treatment significantly down-regulated LIGHT expression, leading to reduced lymphocytes (particularly CD4+ T cells), infiltrating into the hepatic inflammation and inhibited NF-kappaB activation and expression. We postulated that blockade of LIGHT/HVEM signaling by LTbetaR-Ig may ameliorate hepatitis by down-regulating LIGHT expression, and therefore we envision that LTbetaR-Ig would prove to a promising strategy for the clinical treatment of human autoimmune hepatitis.

Tumor necrosis factor family members and inflammatory bowel disease

Tumor necrosis factor (TNF) is one of the most potent effector cytokines in the pathogenesis of inflammatory bowel disease (IBD). Previous studies strongly implicate the critical involvement of several TNF family members in human IBD. This review focuses on the recent studies of TNF family members in IBD development. In particular, we discuss the findings about LIGHT (homologous to lymphotoxins, inducible expression, competes with herpes simplex virus glycoprotein D for herpes viral entry mediator, a receptor expressed on T lymphocytes) in the pathogenesis of IBD, and the potential mechanisms by which LIGHT induces IBD. Such mechanisms may also apply to other TNF family members.

Severe T-cell depletion from the PALS leads to altered spleen composition in common marmosets with experimental autoimmune encephalomyelitis (EAE)

Recent data suggest that the spleen is a crucial component of the immune system in the development of experimental autoimmune encephalomyelitis (EAE) in marmoset monkeys. Using immunohistochemistry, we investigated changes in the distribution of leukocytes in the spleen associated with clinical symptoms of EAE. Animals without EAE displayed well-developed T- and B-cell areas, germinal centers and red pulp. In contrast, a marked depletion of periarteriolar T cells with preservation of other elements was found in animals with clinical EAE. These findings suggest that immune responses within the spleen are impaired during a paralysing inflammatory process in the central nervous system.

Critical roles for IFN-beta in lymphoid development, myelopoiesis, and tumor development: links to tumor necrosis factor alpha

We have generated mice null for IFN-beta and report the diverse consequences of IFN-beta for both the innate and adaptive arms of immunity. Despite no abnormalities in the proportional balance of CD4 and CD8 T cell populations in the peripheral blood, thymus, and spleen of IFN-beta-/- mice, activated lymph node and splenic T lymphocytes exhibit enhanced T cell proliferation and decreased tumor necrosis factor alpha production, relative to IFN-beta+/+ mice. Notably, constitutive and induced expression of tumor necrosis factor alpha is reduced in the spleen and bone marrow (BM) macrophages, respectively, of IFN-beta-/- mice. We also observe an altered splenic architecture in IFN-beta-/- mice and a reduction in resident macrophages. We identify a potential defect in B cell maturation in IFN-beta-/- mice, associated with a decrease in B220+ve/high/CD43-ve BM-derived cells and a reduction in BP-1, IgM, and CD23 expression. Circulating IgM-, Mac-1-, and Gr-1-positive cells are also substantially decreased in IFN-beta-/- mice. The decrease in the numbers of circulating macrophages and granulocytes likely reflects defective maturation of primitive BM hematopoiesis in mice, shown by the reduction of colony-forming units, granulocyte-macrophage. We proceeded to evaluate the in vivo growth of malignant cells in the IFN-beta-/- background and give evidence that Lewis lung carcinoma-specific tumor growth is more aggressive in IFN-beta-/- mice. Taken altogether, our data suggest that, in addition to the direct growth-inhibitory effects on tumor cells, IFN-beta is required during different stages of maturation in the development of the immune system.

SLE - Complex cytokine effects in a complex autoimmune disease: tumor necrosis factor in systemic lupus erythematosus

Tumor necrosis factor (TNF) is a proinflammatory cytokine and a B-cell growth factor. It has numerous possible effects on T lymphocytes and dendritic cells, and it influences apoptosis. These differential effects may in part explain why patients under TNF-blocker therapy can develop autoantibodies to nuclear antigens, and may shed some light on the finding that low TNF fosters autoimmune disease in some mouse strains. On the contrary, TNF is increased in the blood and in the inflamed kidneys of systemic lupus erythematosus patients. Several studies in lupus-prone mice other than the F1 generation of New Zealand Black mice crossed with New Zealand White mice suggest that TNF is highly proinflammatory in the efferent limb and is potentially detrimental in lupus organ disease. Therefore, TNF blockade probably constitutes an efficacious therapeutic option.

The regulation of T cell homeostasis and autoimmunity by T cell-derived LIGHT

Costimulatory molecules on antigen-presenting cells (APCs) play an important role in T cell activation and expansion. However, little is known about the surface molecules involved in direct T-T cell interaction required for their activation and expansion. LIGHT, a newly discovered TNF superfamily member (TNFSF14), is expressed on activated T cells and immature dendritic cells. Here we demonstrate that blockade of LIGHT activity can reduce anti-CD3-mediated proliferation of purified T cells, suggesting that T cell-T cell interaction is essential for this proliferation. To test the in vivo activity of T cell-derived LIGHT in immune homeostasis and function, transgenic (Tg) mice expressing LIGHT in the T cell lineage were generated. LIGHT Tg mice have a significantly enlarged T cell compartment and a hyperactivated peripheral T cell population. LIGHT Tg mice spontaneously develop severe autoimmune disease manifested by splenomegaly, lymphadenopathy, glomerulonephritis, elevated autoantibodies, and severe infiltration of various peripheral tissues. Furthermore, the blockade of LIGHT activity ameliorates the severity of T cell-mediated diseases. Collectively, these findings establish a crucial role for this T cell-derived costimulatory ligand in T cell activation and expansion; moreover, the dysregulation of T cell-derived LIGHT leads to altered T cell homeostasis and autoimmune disease.

A critical role for lymphotoxin-beta receptor in the development of diabetes in nonobese diabetic mice

To assess the role of lymphotoxin-beta receptor (LTbetaR) in diabetes pathogenesis, we expressed an LTbetaR-Fc fusion protein in nonobese diabetic (NOD) mice. The fusion protein was expressed in the embryo, reached high levels for the first 2 wk after birth, and then declined progressively with age. High expression of LTbetaR-Fc blocked diabetes development but not insulitis. After the decline in chimeric protein concentration, mice became diabetic with kinetics similar to the controls. Early expression of fusion protein resulted in disrupted splenic architecture. However, primary follicles and follicular dendritic cells, but not marginal zones, developed in aged mice. Hence, LTbetaR signaling is required for diabetes development and regulates follicular and marginal zone structures via qualitatively or quantitatively distinct mechanisms.