IL15 and rheumatoid arthritis: All markers with increased levels in SAP were also increased in SP RA, i.e. IL-1β (81% and 73%, respectively), IL-2 (81% and 68%), IL-1RA (70% and 68%), IL-17 (63% and 64%), IL-4 (67% and 50%), IL-15 (52% and 59%), and IL-2R (48% and 55%).