PRF1 and systemic lupus erythematosus: CD4+CD28− stress-induced, PP5 overexpressing T cells have decreased ERK and JNK pathway signaling, low Dnmt1 levels, and overexpress methylation sensitive genes including KIR2DL4, CD70 and perforin [18,27], similar to the epigenetically altered CD4+CD28+ T cells from patients with active lupus.