Either humoral or cellular immunity, or both, to human cartilage PGs have been detected in patients with RA [65–79], and the two most recent studies reported that the citrullinated version of a dominant arthritogenic (5/4E8) peptide of human cartilage PG [80, 81] induced substantial cytokine (IL-17, IL-22, IL-6, TNFα, IFNγ) production by T cells from the majority of RA patients [78, 79]. Here, IL17A is linked to rheumatoid arthritis.