Lack of pathogenicity of immunodominant T and B cell determinants of the nicotinic acetylcholine receptor q-chain Susanne Gaertner a , Katrien L. de Graaf a , Wolfgang Wienhold a , Karl-Heinz Wiesmu ¨ller b , Arthur Melms a , Robert Weissert a, * a Experimental Neuroimmunology Laboratory, Department of General Neurology, Hertie Institute for Clinical Brain Research, University of Tu ¨bingen, Hoppe-Seyler-Strasse 3, 72076 Tu ¨bingen, Germany b EMC Microcollections, Sindelfinger Strasse 3, 72072 Tu ¨bingen, Germany Received 18 February 2004; accepted 24 March 2004 Abstract The nicotinic acetylcholine receptor (nAChR) is the autoantigen in seropositive myasthenia gravis (MG) that is a T cell-dependent B cell- mediated autoimmune disorder. We tested the immunogenicity and myasthenogenicity of the extracellular and first transmembrane domain of the q-chain 1 – 221 of the nAChR in inbred and MHC congenic rat strains. Immunodominant T and B cell determinants did not induce experimental autoimmune myasthenia gravis (EAMG), although immunization resulted in strong Th1 and B cell responses, which could be mapped with overlapping peptides of the nAChR q-subunit in eight different rat strains. Our data underscores the concept that immunodominant autoantigen-specific T and B cell responses can lack pathogenicity in autoimmune disease and might be of relevance for the physiological integrity of the organism. D 2004 Published by Elsevier B.V. Keywords: Rodent; Autoimmunity; MHC; Antigens; Peptides; Epitopes 1. Introduction Myasthenia gravis (MG) is the prototypic autoimmune disease with a B cell-mediated T cell-dependent pathogen- esis. The nicotinic acetylcholine receptor (nAChR) is the autoantigen of seropositive MG (Vincent, 2002). This is a pentameric transmembrane receptor at the neuromuscular junction that is composed of aahgy chains (Tzartos et al., 1998a,b). After birth, the nAChR g-chain is replaced by the nAChR q-chain (Gu and Hall, 1988; Missias et al., 1996). In so-called seronegative MG, a new autoantigen has been recently defined called MuSK, a muscle specific tyrosine kinase (Hoch et al., 2001). Antibodies against MuSK can be detected in about 70% of seronegative MG patients. Experimental autoimmune myasthenia gravis (EAMG) is the animal model of MG. Immunizations with highly purified acetylcholine receptor from the electric organ of the electric eel Electrophorus electricus in complete Freund’s adjuvant (CFA) induced EAMG in rabbits (Patrick and Lindstrom, 1973). Immunizations of rats and guinea pigs with nAChR from the electric raye Torpedo californica (T-nAChR) resulted in severe muscular weakness (Lennon et al., 1975). Active immunization with the nAChR a-chain induced EAMG (Lennon et al., 1991; Voltz et al., 1997). Serum transfer from myasthenic patients into mice resulted in muscular weakness (Toyka et al., 1975). Antibodies of patients with seropositive MG were shown to bind to purified nAChR from human muscle and to T-nAChR (Engel et al., 1977) . In about 70% of MG patients, nAChR-specific antibodies are of diagnostic and most likely also pathogenetic relevance (Vincent, 2002). The nAChR a- chain contains the main immunogenic region (MIR) to which pathogenic conformation-dependent high-affinity antibodies are binding at position nAChR a-chain 67–76 (Tzartos et al., 1988a,b). Antibody binding results in either complement-mediated lysis or degradation of receptor mol- ecules (Vincent, 2002). This causes impaired acetylcholine 0165-5728/$ - see front matter D 2004 Published by Elsevier B.V. doi:10.1016/j.jneuroim.2004.03.019 Abbreviations: EAMG, experimental autoimmune myasthenia gravis; MG, myasthenia gravis; MNC, mononuclear cell; MOG, myelin – oligodendrocyte – glycoprotein; nAChR, nicotinic acetylcholine receptor; RT1, MHC of rat; T-nAChR, nAChR from Torpedo californica. * Corresponding author. Tel.: +49-7071-2982043; fax: +49-7071- 600137. E-mail address: robert.weissert@uni-tuebingen.de (R. Weissert). www.elsevier.com/locate/jneuroim Journal of Neuroimmunology 152 (2004) 44 – 56