FXII depletion appears to limit ECMO-related lung pathology. Shown are representative H&E-stained sections of lung tissue harvested immediately after termination of ECMO. (A) Lung tissue from 3 of the 4 control rabbits (the remaining animal was not evaluated because of problems related to tissue processing) in the heparin/protamine cohort had evidence of significant interstitial hemorrhage and edema. In contrast, lung tissue harvested from the 4 FXII ASO-treated animals was relatively intact. (B) Lung tissue from control rabbits in the citrate/calcium cohort paralleled findings in the heparin/protamine cohort with significant interstitial edema and hemorrhage. Lung tissue from the FXI-depleted and heparin-treated animals in this cohort had more moderate evidence of interstitial edema/hemorrhage. In contrast, only 1 of the 4 FXII ASO-treated rabbits in this cohort had evidence of edema (bottom panel). Several of the lungs had evidence of capillary congestion (indicated by an asterisk), a common finding in ECMO. Scale bars, 50 μm; original magnification ×100.