Thus, the purpose of this study was to investigate whether ectopic lymphoid structures in RA synovium are functional by determining whether they: (i) express AID, the enzyme required for SHM and CSR of Ig genes; (ii) support ongoing CSR and the production of high-affinity ACPA; and (iii) remain functional and promote B cell survival, proliferation, and autoantibody production in an RA/SCID chimera model devoid of any new immune cell influx into the synovium and where the ongoing immunological activity of secondary lymphoid organs is excluded. Here, AICDA is linked to rheumatoid arthritis.