Oestrogen up-regulates interleukin-21 production by CD4⁺ T lymphocytes in patients with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease in which abnormal immune responses are mediated by tissue-binding autoantibodies and immune complex deposition. Because most SLE patients are women of child-bearing age, oestrogen has been suggested to play an important role in SLE pathogenesis. One proposed role is to induce B-cell activation, culminating in increased autoantibody production. Interleukin-21 (IL-21) has been shown to be crucial in the differentiation of activated B cells into plasma cells. We therefore hypothesized that oestrogen up-regulates IL-21 production and induces subsequent B-cell activation in SLE patients. Peripheral blood was obtained from 22 SLE patients and 16 healthy controls. Expression levels of IL-21 and its receptor in serum, peripheral blood mononuclear cells, and CD4⁺ T cells were higher in SLE patients than in healthy controls. Exposure of CD4⁺ T cells from SLE patients to 17β-oestradiol led to a dose- and time-dependent increase in IL-21 expression, which was abolished in the presence of mitogen-activated protein kinase (MAPK) (MAPK kinase, p38, Jun N-terminal kinase) inhibitors. B cells from healthy controls showed increased antibody production when they were co-cultured with oestrogen-treated CD4⁺ T cells from SLE patients. Treatment with IL-21 antibody abrogated the increased antibody production of the co-culture systems. This study revealed the association between oestrogen and IL-21 in SLE patients. Oestrogen up-regulates IL-21 expression of CD4⁺ T cells via MAPK-dependent pathways in SLE patients, which in turn induces increased antibody production by B cells.