HMGB1 and rheumatoid arthritis: The aims of the present review are to evaluate the available data about the role of HMGB1 in the crosstalk between gut microbiome and RA-altered immune response, to try to better understand the mechanisms underlying this disease, and to see whether it could represent a therapeutic target and, eventually, whether it would be more cost-effective to inhibit or stimulate the activity of HMGB1 in these conditions.