Serum interleukin-15 is elevated in systemic lupus erythematosus

Objective. To investigate if interleukin-15 (IL-15) (rather than IL-2) is i ncreased in systemic lupus erythematosus (SLE) and might be responsible for immunological abnormalities of SLE such as the increased lymphocytic expre ssion of Bcl-2 and CD25. Methods. Serum IL-15, IL-2 and tumour necrosis factor (TNF) levels of 65 SL E patients, 20 healthy persons and 10 rheumatoid arthritis (RA) patients we re measured by enzyme-linked immunosorbent assay (ELISA). For 25 SLE patien ts, the percentage of CD25+ lymphocytes and the lymphocytic Bcl-2 levels we re simultaneously deter-mined by fluorocytometry. Peripheral blood mononucl ear cells (PBMC) of 15 SLE patients were incubated with or without recombin ant 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 o f the 20 healthy sera (P = 0.0005) and none of the 10 RA sera. Both lymphoc yte 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 ab normalities seen in active SLE.