In the synovium of RA patients, the leucocyte infiltrate releases PAD2 and PAD4, producing large amounts of citrullinated proteins, including fibrinogen, vimentin, collagen type II, and alpha-enolase, which, in turn, activate the immune response through the generation of anti-citrulline antibodies against these modified protein antigens [31]. The gene discussed is PADI2; the disease is rheumatoid arthritis.