HMGB1 and rheumatoid arthritis: Our disclosure of the activity of the CXCL12/HMGB1 heterocomplex in Rheumatoid Arthritis (8), and the fact that it induces a different conformational change in CXCR4 dimers compared to stimulation with CXCL12 alone (6), prompted us to further investigate the downstream signaling events elicited by CXCR4 triggering.