IL-6 and TNF-alpha are proinflammatory cytokines involved in various inflammatory or non-inflammatory disorders characterized by muscle wasting. While infiltrating leukocytes are known to be the major source of these cytokines, it is unclear whether muscle cells also contribute to local inflammation. In this study, we first showed that cultured muscle cells and naive mouse muscle tissue were capable of producing IL-6 and TNF-alpha. We demonstrated an increased expression of IL-6 and TNF-alpha on muscle sections of C57BL/6J mice immunized with acetylcholine receptor (AChR) in the complete Freund's adjuvant (CFA) or with CFA only. In the presence of IL-6 or TNF-alpha, cultured AChR-expressing mouse (G-8) and human (TE671) skeletal muscle cells showed significantly decreased alpha-bungarotoxin-binding sites as measured by cellular ELISA. Moreover, IL-6- or TNF-alpha-treated muscle cells displayed a considerable increase in apoptotic cell ratios. Collectively, this study suggests a direct role for these two cytokines in muscle cell destruction and a possibility of muscle cell damage via an autocrine fashion. (c) 2006 Elsevier Ltd. All rights reserved.