Breakdown of Tolerance to a Self-Peptide of Acetylcholine Receptor α-Subunit Induces Experimental Myasthenia Gravis in Rats

Abstract

Experimental autoimmune myasthenia gravis (EAMG), a model for human myasthenia (MG), is routinely induced in susceptible rat strains by a single immunization with Torpedo acetylcholine receptor (TAChR). TAChR immunization induces anti-AChR Abs that cross-react with self AChR, activate the complement cascade, and promote degradation of the postsynaptic membrane of the neuromuscular junction. In parallel, TAChR-specific T cells are induced, and their specific immunodominant epitope has been mapped to the sequence 97–116 of the AChR α subunit. A proliferative T cell response against the corresponding rat sequence (R97–116) was also found in TAChR-immunized rats. To test whether the rat (self) sequence can be pathogenic, we immunized Lewis rats with R97–116 or T97–116 peptides and evaluated clinical, neurophysiological, and immunological parameters. Clinical signs of the disease were noted only in R97–116-immunized animals and were confirmed by electrophysiological signs of impaired neuromuscular transmission. All animals produced Abs against the immunizing peptide, but anti-rat AChR Abs were observed only in animals immunized with the rat peptide. These findings suggested that EAMG in rats can be induced by a single peptide of the self AChR, that this sequence is recognized by T cells and Abs, and that breakdown of tolerance to a self epitope might be an initiating event in the pathogenesis of rat EAMG and MG.

Pixantrone (BBR2778) Reduces the Severity of Experimental Autoimmune Myasthenia Gravis in Lewis Rats

“…The effect of PIX has never been investigated in EAMG, the animal model of MG. EAMG can be induced in Lewis rats by immunization with purified TAChR or with the immunodominant epitope 97-116 of the rat AChR ␣ subunit (6,25). In the present study we investigated the potential immunomodulatory effect of PIX in TAChR-induced model of EAMG.…”

“…In the present study we investigated the potential immunomodulatory effect of PIX in TAChR-induced model of EAMG. We first addressed the issue of PIX effect on the in vitro proliferative responses of a T cell line specific for peptide 97-116 (6). PIX inhibited T cell responses in a dose-dependent fashion up to the complete suppression of the proliferation (Fig.…”

“…Clinical scoring was based on the presence of tremor, hunched posture, muscle strength, and fatigability. Fatigability was assessed after exercise (repetitive paw grips on the cage grid) for 30 s. Disease severity was graded as follows: grade 0, normal strength and no fatigability; grade 1, mildly decreased activity and weak grip or cry; grade 2, clinical signs present at rest; grade 3, severe clinical signs at rest, no grip, moribund; and grade 4, dead (6). Each animal was weighed and evaluated at the beginning of each experiment and twice weekly; EAMG was confirmed by Edrophonium chloride test.…”

“…The 97-116 peptide of the rat AChR ␣ subunit is a T cell immunodominant and myasthenogenic epitope (6). T cell lines grown from rat 97-116 peptide-immunized rats (n ϭ 2) were challenged with 5 g/ml specific peptide and 2 g/ml Con A in a T cell proliferation test by [ 3 H]thymidine incorporation in the presence of increased amounts of PIX (0.01-10 M).…”

“…In particular, we studied the ability of PIX to modulate Ag-specific T cell responses in vitro vs peptide 97-116, an immunodominant and myasthenogenic T cell epitope of the rat AChR ␣ subunit (6), and the effects on immune cell function in the spleen and lymph nodes of PIX-treated rats after TAChR immunization. Finally, we tested the ability of PIX to modify the course of rat EAMG.…”