One potential mechanism by which peripheral inflammatory signals might mediate NP-SLE could be through altered activity of indoleamine-2,3-dioxygenase (IDO, see Figure 1), an enzyme that is critical in shaping the inflammatory environment [23,24] and the neuroimmune interactions engendering NP-SLE [25]. The gene discussed is IDO2; the disease is systemic lupus erythematosus.