The main findings of this study were: (1) the novel PAR2 immunoassay was specific towards the neo-epitope and technically robust, (2) PRO-PAR2 was released by matriptase cleavage in vitro and detected by the assay, (3) PRO-PAR2 was released from human synovial membrane explants after treatment with matriptase, (4) PRO-PAR2 levels were increased in RA patients compared to healthy individuals, (5) treatment with tocilizumab led to reduced PRO-PAR2 levels. The gene discussed is F2RL1; the disease is rheumatoid arthritis.