Serum interleukin‐15 is elevated in systemic lupus erythematosus

Objective. To investigate if interleukin‐15 (IL‐15) (rather than IL‐2) is increased in systemic lupus erythematosus (SLE) and might be responsible for immunological abnormalities of SLE such as the increased lymphocytic expression of Bcl‐2 and CD25. Methods. Serum IL‐15, IL‐2 and tumour necrosis factor (TNF) levels of 65 SLE patients, 20 healthy persons and 10 rheumatoid arthritis (RA) patients were measured by enzyme‐linked immunosorbent assay (ELISA). For 25 SLE patients, the percentage of CD25 + lymphocytes and the lymphocytic Bcl‐2 levels were simultaneously determined by fluorocytometry. Peripheral blood mononuclear cells (PBMC) of 15 SLE patients were incubated with or without recombinant IL‐15 and the influence on Bcl‐2 and CD25 was determined. Results. IL‐15 was found to be elevated in 25 SLE sera (38%), but in none of the 20 healthy sera (P = 0.0005) and none of the 10 RA sera. Both lymphocyte CD25 and Bcl‐2 expression significantly correlated with serum IL‐15 and were increased by recombinant IL‐15. Conclusion. Serum IL‐15 may in part be responsible for the immunological abnormalities seen in active SLE.