Résumé :
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Communication n° 371 Introduction: Myasthenia gravis (MG) is caused primarily by autoantibodies directed against the nicotinic acetylcholine receptor (AChR), with additional anti-muscle autoantibodies being detected in some MG patients. The role of non-AChR autoantibodies remains to be elucidated. Objectives: To investigate the morphological and cytotoxic effects of myasthenia gravis patient sera of different autoantibody composition on human muscle cells in culture. Methods: Normal human primary muscle cell cultures were exposed to MG patient sera or control sera and observed by light microscopy, following crystal violet staining. DAPI and FITC-phalloidin staining were used to examine changes in nuclear morphology (induction of apoptosis) and the actin cytoskeleton respectively, by fluorescence microscopy. Results: Sera from the most severely affected MG patients induced a dramatic change in cell morphology from the typical elongated muscle phenotype observed in control cultures to an irregular, more retracted phenotype. Apparent inclusion bodies and vesicles were observed in MG treated cultures, and also a reduction in total cell number, indicating a cytotoxic effect. Whilst changes in nuclear morphology were observed, they were not typical of the induction of apoptotic cell death. The organisation of the actin cytoskeleton was severely disrupted upon treatment with sera from the most severely affected patients. These effects were dose- and time-dependent, and were not complement-mediated, since heat inactivation of sera had no effect. The observed effects appeared to correlate with disease severity, the greatest effects observed with sera obtained from patients during MG crisis. Conclusions: MG patient sera induce changes in cell shape, inclusion body and vesicle formation, and disruption of the actin cytoskeleton, in primary human muscle cell cultures. The mechanisms by which such effects occur, and the specific autoantibodies involved, are currently under investigation.
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