IL-6 protein is increased in muscle from MG patients and is induced by MG sera in muscle cells. The IL-6 levels were determined by ELISA in protein extracts of human muscle biopsies (A) or in the medium of myoblasts cultured for 24 h with sera from SPMG or SNMG patients, or other skeletal muscle diseases or healthy controls diluted 1/100 in the culture medium (B). Each serum was tested twice. The significance was evaluated using t-tests between groups. **p < 0.01; *p < 0.05.