Indeed, we have previously shown that high MC in synovia are associated with the infiltration of lympho-myeloid cells, both ex vivo in early untreated RA patients and in vivo in animal models of antigen induced arthritis, and MCs were able to activate B cells inducing the production of ACPA autoantibodies (Rivellese et al., 2018). This evidence concerns the gene PRTN3 and rheumatoid arthritis.