The presence of ectopic lymphoid structures in RA synovitis is associated with the activation of immunologically relevant mechanisms: expansion of PD-1hi CXCR5- “peripheral helper” CD4 T cells (23), production of inflammatory cytokines (19, 20), B cell maturation (24–26) and ACPA production (24). This evidence concerns the gene PRTN3 and rheumatoid arthritis.