The enhanced production of IFN-γ in patients with SLE was also observed for CD28 co-stimulation, with a significant difference between patients with inactive SLE and normal control individuals (median values: active SLE, 370.9 pg/ml; inactive SLE, 1292.6 pg/ml; normal control individuals, 171.6 pg/ml; P < 0.01, patients with inactive SLE versus normal control individuals). This evidence concerns the gene CD28 and systemic lupus erythematosus.