The WT, PARP1+/-, and PARP1-/- mice were genotyped to confirm the presence of two, one and no copies of the PARP1 gene (S1A Fig). We then evaluated the effect of Tc infection on the levels of PARP1 mRNA, protein, and activity in WT and PARP1-/- mice. In PARP1-/- mice, PARP1 mRNA and protein levels remained undetectable before or after Tc infection (Fig 1A–1C). In chronically infected WT (vs. uninfected WT) mice, the myocardial levels of PARP1 mRNA and protein were increased by 220% and 68.8%, respectively (Fig 1A–1C, all, p<0.001). Tissue fractionation/Western blotting showed 130%, 230%, and 141% increase in PARP1 levels in the myocardial cytosolic, nuclear, and mitochondrial fractions of WT.Tc (vs. WT) mice (Fig 1D & 1E, all, p<0.01). Protein PARylation is an indicator of PARP1 activity. Our data showed 43-fold, 44-fold and 30-fold increase in protein PARylation levels, respectively, in the myocardial cytosolic, nuclear, and mitochondrial fractions of WT.Tc (vs. WT) mice (Fig 1F–1K, all, p<0.001). The PARP1-/- mice exhibited a basal PARylation level that was not substantially increased in response to chronic infection (Fig 1F–1K). These results suggest that PARP1 expression and PARylation activity were increased in myocardial fractions (cytosolic, nuclear and mitochondrial) of chagasic WT mice. Other members of the PARP family likely contributed to the slight increase in PARylation level observed in chronically infected PARP1-/- mice..