CD4 and systemic lupus erythematosus: In CD4+ T cells from healthy people engagement of the costimulatory molecule CD28 leads to rapid upregulation of aerobic glycolysis [2], which is in stark contrast to T cells from patients with SLE which display a chronically activated phenotype, upregulated calcium signaling, enhanced tricarboxylic acid (TCA) cycle activity and dependency on oxidative phosphorylation (OXPHOS) to meet their energetic needs [12].