Antimitochondrial Abs (AMAs)—the diagnostic hallmark of PBC—are largely of IgG origin.32 AMAs are not restricted to one IgG subclass, but AMA-specific IgG3 titers are higher than IgG1 or IgG2 and associated with a more severe disease course.33,34. Here, IGHG3 is linked to primary biliary cholangitis.