These autoantibodies, consisting of mainly IgM, IgA (IgA1 and IgA2) and IgG (IgG1, IgG2, IgG3, and IgG4), bind to exogenous antigens (e.g., bacterial) acting as a first line of immune defense against infections and can be polyreactive (24). Here, IGHG3 is linked to infection.