IL21 and systemic lupus erythematosus: Measurement of the serum IL-21 levels in primary SS (n = 40), SLE (n = 38), and RA (n = 40) patients and healthy controls (n = 20) by ELISA revealed mean IL-21 levels of 646 ± 637, 454 ± 534, 342 ± 322, and 74 ± 132 pg/ml, respectively (Figure 1).