LYN and Autoimmunity: Similarly, deleting IL-21, a key regulator of GC responses and plasma cell formation (120), in Lyn−/− mice leads to reduced IgG ANAs but does not alleviate IgM ANA, plasmacytosis, or glomerulonephritis (121), suggesting that IgM and/or IgA can mediate the development of autoimmunity (122).