Regular articleExogenous soluble tumor necrosis factor receptor type I ameliorates murine experimental autoimmune neuritis
Introduction
Tumor necrosis factor (TNF), initially characterized as having antitumor activity, is a pleiotropic proinflammatory cytokine, produced mainly by activated macrophages and T cells, that mediates a wide range of biological functions Vassalli 1992, Tracey and Cerami 1993. TNF plays a pivotal role in serious acute as well as chronic inflammatory conditions and is thought to be involved in the pathogenesis of autoimmune and inflammatory diseases Tracey and Cerami 1993, Zhu et al 1997, Zhu et al 1998, Hilliard et al 2001, Kassiotis and Kollias 2001. High levels of these molecules in serum and also at local sites of inflammation have been associated with inflammatory processes such as Guillain–Barre syndrome (GBS), multiple sclerosis (MS), rheumatoid arthritis (RA), and diabetes Vassalli et al 1992, Tracey and Cerami 1993, Hartung et al 1995, Ossege et al 2000, Feldmann and Maini 2001.
The biological effects of TNF are mediated by its binding to two distinct cell surface receptors. The receptor molecules are named according to their molecular weight as TNF receptor (TNFR) I (p55, about 55 kDa) and TNFR II (p75, about 75 kDa) Tartaglia and Goeddel 1992, Smith et al 1994. Both TNF receptors (TNFRs) are expressed on various cells types, especially on the surfaces of activated CD4 and CD8 positive T-cell subsets (Ware et al., 1991). After cell activation by TNF itself, these TNFRs are cleaved by metalloproteinases and remain as soluble forms (sTNFRs) in sera and body fluids (Porteu et al., 1990). Subsequently, sTNFRs often function as TNF antagonists by competing for ligand with membrane-bound TNFR both in vitro and in vivo (Kohno et al., 1990). These receptors are thought to protect cells from TNF and to block the activity of this cytokine after its release into the circulation Van Zee et al 1992, Hunger et al 1997. The results of some studies have shown that sTNFRs are potent inhibitors of experimental autoimmune encephalomyelitis (EAE), an inflammatory disease of the central nervous system Baker et al 1994, Selmaj et al 1995, autoimmune diabetes (Hunger et al., 1997), RA Mori et al 1996, McComb et al 1999, and experimental autoimmune thyroiditis (Zaccone et al., 2002). Clinical trials with soluble TNFRs have demonstrated its efficacy in treating human RA Moreland et al 1996, Moreland et al 1997, Weinblatt et al 1999, Feldmann and Maini 2001. However, treatment with Lenercept, a recombinant TNF receptor P55 immunoglobulin fusion protein (sTNFR-IgG P55), failed to show benefit in MS patients, who showed a worsening of the disease (The Lenercept Multiple Sclerosis Study Group). The reason why Lenercept failed is not known.
Polyethylene glycol (PEG) sTNFRI is a recombinant E. coli form of the “high affinity” p55 (sTNFRI) to which a 30-kDa PEG molecule is attached Martin et al 1998, Edwards et al. Preclinical study data in rodents have demonstrated that PEG sTNFRI is efficacious in ameliorating chronic inflammatory diseases, including RA Moreland et al 1997, Bendele et al 1999.
Experimental autoimmune neuritis (EAN) is a T-cell-mediated, acute, demyelinating inflammatory disease of the peripheral nervous system (PNS) that serves as a model for human GBS. The close clinical, histopathological, and electrophysiological similarities between EAN and GBS make EAN an especially suitable model for studying pathogenic mechanisms and novel strategies for treating GBS. In previous studies, we showed that a good relationship between the clinical activity of EAN and high levels of TNF-α production in peripheral nerves was consistent with a disease-promoting role for TNF-α Zhu et al 1997, Zhu et al 1998. Pharmacological compounds such as linomide and rolipram strongly suppressed the severity of clinical EAN, associated with suppressed TNF-α production in vivo and in vitro Zhu et al 1999, Zou et al 2000a. In contrast, we found that TNF-α receptor I deficiency led to lethal EAN in mice (unpublished data). In the present study, we used PEG sTNFR I to investigate further the effects of TNF-α and sTNFR I on the development of EAN in C57BL/6 mice. Our results show beneficial effects of sTNFR I administration that result in a substantially decreased severity of clinical EAN.
Section snippets
Antigens and immunoreagents
The neuritogenic P0 glycoprotein peptides, corresponding to amino acids 180–199 of the rat PNS myelin P0 protein, were synthesized by solid-phase stepwise elongation using a Tecan peptide synthesizer (Multisyntech, Bochum, Germany). PEG sTNFR I was kindly provided by Amgen, Inc., Thousand Oaks, CA, USA.
Induction of EAN and assessment of clinical signs
For EAN induction, we used male C57BL/6 mice bred at the animal housing facilities of the Microbiology and Tumor Biology Center, Karolinska Institute, Stockholm, Sweden. All mice were 6–8 weeks
sTNFR I treatment suppresses the severity of clinical EAN
To explore the roles of sTNFR I in the initiation and development of EAN, C57BL/6 mice were immunized twice with P0 peptide 180–199 in FCA and treated with sTNFR I either before the disease began, i.e., on Day 2 before immunization (prevention group), or afterward (Day 14 pi) (treatment group). All immunized mice acquired the clinical symptoms of EAN on Day 16 pi. Notably, both sTNFR I-treated groups exhibited less severe disease than PBS-treated control mice, as indicated by the former groups’
Discussion
In the present study, we show that TNF is a pivotal agent in the development of EAN and that sTNFR I treatment effectively decreases the severity and shortens the duration of EAN. These beneficial effects of sTNFR I on ameliorating EAN were associated with suppression of P0 peptide-specific T-cell proliferation, as well as decreases in Th1 cytokine IFN-γ secretion, TNF-α production, and inflammatory cell infiltration into the PNS. Both sTNFR I treatment schedules, i.e., 2 days before and 14
Acknowledgements
We thank Amgen, Inc., Thousand Oaks, CA, USA, for providing PEG sTNFR I. This study was supported by grants from the Swedish Medical Research Council (K2001-16X-13133-03A, K2001-99PU-12720-04B, and K2002-16X-13133-04B) and funds from Konung Gustaf V:s och Drottning Victorias Foundation.
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