- IL-21 is significantly associated with anemia (105). - Increasing level of IL-21 is observed in PBMCs of SLE patients (106). - IL-21 may synergise with TLR-9 signalling in the production of plasma B cells (106). - Expansion of circulating CD4+ T-cells producing IL-21 is observed in SLE patients (107). - IL-21 produced by distinct cellular CD4+ T-cell subsets are correlated with T and B cell subsets alterations in SLE (107). This evidence concerns the gene CD4 and systemic lupus erythematosus.