T helper 17 (Th17) cells producing IL-17 are highly proinflammatory effector T cells associated with a number of autoimmune diseases [179], and they can provide help to B cells and mediate class switching to IgG1 and IgG2b as well as to a lesser extent to IgG2a and IgG3 [180]. Here, IL17A is linked to autoimmune disease.