Positive and negative implications of tumor necrosis factor neutralization for the pathogenesis of multiple sclerosis.

Multiple sclerosis (MS) is a progressive, presumably autoimmune, degenerative disease of the central nervous system (CNS). The mechanisms which trigger the disease are unknown, but the pathology of MS is caused by the host's own immune system, which invades the CNS and attacks the myelin sheath that protects and insulates the axons of the nerve cells. Although this inflammatory assault selectively destroys myelin, it is believed that the neurological deficits of MS are rather the consequence of damage to axons, which occurs secondary to inflammation. The inflammatory mediators are generally secreted by myelin-specific, CD4+ T cells, CD8+ T cells, macrophages and activated glial cells and include a large number of cytokines, chemokines and other proinflammatory proteins.

Adenovirus-based overexpression of tissue inhibitor of metalloproteinases 1 reduces tissue damage in the joints of tumor necrosis factor alpha transgenic mice.

OBJECTIVE: Rheumatoid arthritis is a prototype of a destructive inflammatory disease. Inflammation triggered by the overexpression of tumor necrosis factor alpha (TNFalpha) is a driving force of this disorder and mediates tissue destruction. Since matrix metalloproteinases (MMPs) are among the molecules activated by TNFalpha, we hypothesized that overexpression of their natural inhibitor, tissue inhibitor of metalloproteinases 1 (TIMP-1), in TNFalpha transgenic mice could inhibit the development of destructive arthritis. METHODS: Systemic treatment was carried out by replication-defective adenoviral vectors for TIMP-1, beta-galactosidase, or phosphate buffered saline (PBS), which were applied once at the onset of arthritis. Clinical, serologic, radiologic, and histologic outcomes were assessed 18 days after the treatment. RESULTS: The AdTIMP-1 group showed significantly reduced paw swelling and increased grip strength compared with the 2 control groups, whereas total body weight, TNFalpha, and interleukin-6 levels were similar in all 3 groups. Radiographic assessment revealed a significant reduction of joint destruction in the AdTIMP-1 group; this was confirmed by histologic analyses showing reduced formation of pannus and erosions in the AdTIMP-1 group compared with the AdLacZ and PBS control groups. The formation of arthritis-specific autoantibodies to heterogeneous nuclear RNP A2 was not observed in the AdTIMP-1 group but was present in the 2 control groups. CONCLUSION: These results indicate a central role of MMPs in TNFalpha-mediated tissue damage in vivo and a promising therapeutic role for TIMP-1.

Methotrexate specifically modulates cytokine production by T cells and macrophages in murine collagen-induced arthritis (CIA): a mechanism for methotrexate-mediated immunosuppression.

Immunosuppressive therapy with methotrexate (MTX) has been established as effective treatment for patients with rheumatoid arthritis. To analyse the therapeutic potential and mechanisms of action of MTX, we determined serum cytokine levels and cytokine production by splenic T cells and macrophages in untreated and MTX-treated mice. Furthermore, we assessed the role of MTX in a murine model of experimental arthritis induced by collagen type II (CIA). MTX reduced spontaneous and IL-15-induced tumour necrosis factor (TNF) production by splenic T cells but not by macrophages from healthy mice in vitro in a dose-dependent manner. In contrast, interferon-gamma (IFN-gamma) production was less strikingly reduced and IL-4 production was virtually unaffected. In addition, treatment of healthy mice with MTX in vivo led to reduced TNF serum levels and diminished TNF production by splenic T cells and macrophages. Intraperitoneal administration of MTX prior to the onset of arthritis completely prevented clinical and pathological signs of CIA. This was associated with a striking reduction of TNF production by spleen cells from MTX-treated mice. The role of TNF in MTX-mediated effects on cytokine production was further underlined by the finding that MTX effects on IFN-gamma production were augmented in TNF-transgenic mice but abrogated in mice in which the TNF-alpha gene had been inactivated by homologous recombination. Thus, MTX specifically modulates spontaneous and IL-15-induced TNF-alpha production in mice and prevents experimental murine CIA. These data suggest that TNF production by T cells is an important target of MTX and may serve as a basis to understand and further analyse MTX-mediated mechanisms of immunosuppression in patients with RA.

Predominant pathogenic role of tumor necrosis factor in experimental colitis in mice.

Antibodies to tumor necrosis factor (TNF)-alpha have been recently proposed as effective treatment for patients with Crohn's disease. Here, we analyze the functional role of TNF-alpha in a mouse model of chronic intestinal inflammation induced by the hapten reagent 2,4,6,-trinitrobenzene sulfonic acid (TNBS) that mimics some characteristics of Crohn's disease in humans. Macrophage-enriched lamina propria (LP) mononuclear cells from mice with TNBS-induced colitis produced 10-30-fold higher levels of TNF-alpha mRNA and protein than cells from control mice. When mice with chronic colitis were treated by intraperitoneal injection of antibodies to TNF-alpha, an improvement of both the clinical and histopathologic signs of disease was found. Isolated macrophage-enriched LP cells from anti-TNF-alpha-treated mice produced strikingly less pro-inflammatory cytokines such as interleukin (IL)-1 and IL-6 in cell culture. The predominant role of TNF-alpha in the mouse TNBS-induced colitis model was further underlined by the finding that striking colonic inflammation and lethal pancolitis was induced in TNF-alpha-transgenic mice upon TNBS treatment. Conversely, no significant TNBS-induced colitis could be induced in mice in which the TNF-alpha gene had been inactivated by homologous recombination. Complementation of TNF-alpha function in TNF-/- mice by the expression of a mouse TNF-alpha transgene was sufficient to reverse this effect. Taken together, the data provide direct evidence for a predominant role of TNF-alpha in a mouse model of chronic intestinal inflammation and encourage further clinical trials with antibodies to TNF-alpha for the treatment of patients with Crohn's disease.

Dissection of the pathologies induced by transmembrane and wild-type tumor necrosis factor in transgenic mice.

With increasing awareness that seemingly diverse immune-mediated diseases involve similar pathogenetic mechanisms, and the identification of a growing number of key effector molecules, it is becoming possible to design and generate effective transgenic models for such diseases. Tumor necrosis factor (TNF) plays a prominent role in immune and host defense responses and there is strong evidence that abnormal TNF production contributes to disease initiation and progression in rheumatoid arthritis, systemic inflammatory response syndrome, diabetes, multiple sclerosis, and many other immune-mediated disorders. The generation of TNF transgenic mice, in which TNF production is deregulated, has provided us with direct evidence that, in vivo, this cytokine can indeed trigger the development of such complex disease phenotypes. Transgenic mice that have been engineered to overexpress human or murine TNF molecules in peripheral joints, T cells, or neurons of the central nervous system represent important animal models for human rheumatoid arthritis, systemic inflammation, and multiple sclerosis, respectively. In addition to establishing a central role for TNF in such diseases, these animal models have already proved valuable for identifying additional important disease-effector molecules, and for gaining an insight into the complex in vivo mechanisms that are involved in disease pathogenesis. For example, in the case of arthritis, TNF has been found to transmit its pathogenic effects entirely through interleukin-1, which may therefore represent an additional important target for therapeutic intervention in the human disease. In summary, TNF transgenic models of human disease are expected to serve as important in vivo tools for defining details of disease pathogenesis, potential targets for therapeutic intervention and for evaluating the possible involvement of additional genetic and environmental factors on the disease state.

Antibodies to acetylcholinesterase cross-reacting with thyroglobulin in myasthenia gravis and Graves's disease.

In the present study we analysed by ELISA the ability of sera from 50 patients with myasthenia gravis (MG), 20 with Hashimoto's thyroiditis (HT), 53 with Graves' disease (GD) and 36 healthy controls (CR) to react with acetylcholinesterase (AChE) from Electrophorus electricus and human thyroglobulin (Tg). Significantly increased anti-AChE activity was exhibited by a high proportion of MG (IgG 36%) and GD (IgG 21%) sera, while increased anti-Tg activity was detected in all three patient groups (MG, IgG 26% and IgA 26%; HT, IgG 85% and IgA 40%; and GD, IgG 51%). Interestingly, a significant proportion of MG and GD sera exhibited both IgG anti-AChE and anti-Tg activities (MG, 18%; P < 0.001; and GD, 15%; P < 0.001, versus CR, 0%). This bi-reactivity was exhibited by anti-AChE antibodies cross-reacting with Tg (anti-AChE/Tg activity); (i) serum anti-AChE activity was effectively inhibited by soluble Tg, and (ii) affinity-purified anti-Tg antibodies cross-reacted with AChE. Cross-reactivity seems to be a property of pathological (auto)antibodies; induced (rabbit) antibodies to AChE or Tg were highly monospecific. Analysis of clinical data showed that increased IgG anti-AChE/Tg activity was well associated with: (i) overlapping GD in MG (P < 0.02), and (ii) ophthalmopathy in GD (P < 0.01). In contrast, no correlation was noted in MG between anti-AChE activity units and anti-Tg activity units or acetylcholine receptor antibody titres. The clinical significance of anti-AChE/Tg antibodies remains to be elucidated.

Increased natural autoantibody activity to cytoskeleton proteins in sera from patients with necrobiosis lipoidica, with or without insulin-dependent diabetes mellitus.

Necrobiosis lipoidica (NL), a skin disease, is associated with insulin-dependent diabetes mellitus (IDDM). Natural autoantibody (NAb) activity in sera from 16 patients suffering from NL, with or without IDDM, was compared to that in sera from 41 patients with IDDM and 43 healthy controls. Isotype-specific enzyme-linked immunosorbent assays (ELISAs) were used to detect NAbs against actin, myosin, keratin, desmin, troponin, tropomyosin, thyroglobulin, insulin, single-stranded DNA and the hapten trinitrophenyl. NAb activity was significantly higher in sera from patients with NL (either with or without IDDM), compared with that detected in sera from patients with IDDM which was similar to that of healthy individuals. High proportion of NL sera exhibited increased IgG anti-tropomyosin (69%), anti-troponin, anti-desmin and anti-keratin (50% each), anti-insulin (44%) and anti-trinitrophenyl (31%) activities, as well as increased IgA and IgM anti-keratin activities (26% and 31%, respectively). The great majority (88%) of positive sera were polyreactive and contained NAbs, polyspecific and monospecific (as demonstrated by immunoadsorption studies), belonging to more than one isotype; there was no predominant serological reactivity pattern. In conclusion, increased NAb activity to cytoskeleton proteins is associated with the dermatological disease NL and not to the overlapping autoimmune disease (IDDM). The origin and significance of these NAbs is discussed.

Transgenic and knockout analyses of the role of TNF in immune regulation and disease pathogenesis.

Transgenic mutagenesis in whole animals has become without doubt the most rewarding approach to analyse gene structure, expression, and function. In the TNF field, much of what we now question about TNF/TNF receptor function is based, to a large extent, on what we have already learned by overexpressing these molecules in transgenic mice or by ablating their expression in knockout systems. In addition, a clearer view of the involvement of these molecules in disease pathogenesis has emerged, and useful models for human disease have been generated. In this overview, we summarise our experience with TNF transgenic and knockout systems, and highlight advances made in our understanding of the role played by TNF and its receptors in immune regulation and in the pathogenesis of infectious, inflammatory, and autoimmune disease.