Despite accumulating evidence for the importance of PAD2 for T and B cell function, a requirement for PAD2 has not been evaluated in an IL-17-driven [16] model of rheumatoid arthritis with pathogenic autoantibodies [17], such as collagen-induced arthritis (CIA), whereas PAD4 was shown to be required for full arthritis severity in this model [18]. The gene discussed is PADI4; the disease is rheumatoid arthritis.