It is important to note that lupus CD4+ T cells were primed to receive and activate IL-2 signaling as evidenced by the upregulation of CD25 and enhanced IL-2-induced STAT5 phosphorylation during Treg differentiation even though the CD4+CD25+FOXP3+ Treg population was depleted in SLE patients. Here, CD4 is linked to systemic lupus erythematosus.