To determine soluble anti-MuSK antibody effects on MuSK-CAART activity, we performed cytotoxicity assays in the presence of a physiologic concentration (10 mg ml−1) of polyclonal IgG from patients with MG, or individual or mixed monoclonal antibody (mAb), at concentrations within or exceeding the expected range for autoantigen-specific IgG (0.2–25 μg ml−1). Here, MUSK is linked to myasthenia gravis.