MUSK and Autoimmunity: Furthermore, pathogenic mechanisms were described for serum or IgG from patients with IgG4 autoimmunity that are likely not caused by IgG4 subclass antibodies as they depend on divalent binding or Fc effector function (Figure 3B, endocytosis of antigen and complement activation) or have been demonstrated using purified or cloned patient IgG1–3 [e.g., Dsg3-IgG1 (221), ADAMTS13-IgG1 (69), Lgi1-IgG3 (275), MuSK-IgG1–3 (3), or Iglon5-IgG1 (134)].