MZB1 and systemic lupus erythematosus: Although the role of MZB1 in RA is yet to be clarified; its previously described role in SLE during the maintenance of splenic marginal zone B cells, plasma cells and autoantibody production (Miyagawa-Hayashino et al., 2018), suggest this molecule could play a central role in maintaining ectopic lymphoid structures, in the RA synovium.