In mice with experimental autoimmune encephalomyelitis (EAE), the murine model for MS, administration of capsular polysaccharide A (PSA), the symbiosis factor for human intestinal commensal Bacteroides fragilis, elicits immunotolerance by promoting expansion and accumulation of CD39+CD4+ cells in CNS lymphoid-draining sites [83]. The gene discussed is ENTPD1; the disease is myeloid sarcoma.