As described by other groups [28,29], we observed that the concentration of IL-21 was significantly higher in sera from SLE patients than in those of healthy individuals (278±106 pg/ml in SLE patients, n=88 vs 146±17 pg/ml in healthy individuals, n=40, p<0.0001; Figure 5A). Here, IL21 is linked to systemic lupus erythematosus.