Liu et al. correlated reduced IDO levels to reduced Foxp3 expression in placentae from preeclamptic women and suggested that loss of fetal tolerance in preeclampsia is due to reduced T regulatory cells, however, upon preliminary analysis we observed no significant difference in Foxp3 expression via qPCR in IDO‐KO versus control placentae (IDO‐KO n = 5: 22.5 ± 0.39, vs. control n = 6: 24.3 ± 1.2, P = 0.2201; Liu et al. 2011). Here, IDO1 is linked to preeclampsia.