Kynurenines exert important immunosuppressive functions including inducing Treg proliferation and reducing the activity NK and dendritic cells.19 A possible mechanism for increased IDO activity during a hookworm infection is the upregulation in CTLA-4 expression on Tregs, which has been demonstrated to increase IDO activity in other immune cells.15 This evidence concerns the gene CTLA4 and ancylostomiasis.