IL6 and rheumatoid arthritis: For the 5 studies related to change in the circulating IL-6 level across IL-6-174G/C variants, 3 groups involved Europeans[19,39,40] and the other 2 groups included Asians.[35,41] Four groups provided circulating IL-6 in healthy controls,[19,39–41] and 1 group in RA patients.[35]