IDO1 and serum lipopolysaccharide activity: This study was aimed 1) at comparing circulating EPCs levels between mice with low dose endotoxemia and mice with low dose endotoxemia supplemented with l-kyn, and 2) at assessing the association between hs-CRP and circulating EPCs according to IDO1 activity in a human cohort of patients exposed to variable systemic low-grade inflammation.