TPH1 and rheumatoid arthritis: In preceding investigations, Tph cells have been identified as playing a pivotal pathogenic role in a plethora of autoimmune diseases, including SLE (10), RA (8), IgG4-related disease (11), type 1 diabetes (12), IgA nephropathy (13), psoriasis vulgaris (14), active ulcerative colitis (15) and anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) (20).