*3.1. HO-1 Expression in F4/80+ Peritoneal Cells Inversely Correlate with ROS/RNS Production*

In order to confirm the recruitment of PECs expressing HO-1 to the peritoneum of *F. hepatica*-infected mice, we identified HO-1*<sup>+</sup>* cells by flow cytometry at different time points of the infection. As seen in Figure 1A, the clinical score increased upon infection, although ALT in serum significantly increased only after 21 dpi, demonstrating liver dysfunction. In addition, HO-1*<sup>+</sup>* cells significantly increased in the peritoneal cavity during the infection (Figure 1B,C and Supplementary Figure S1). These cells were mainly composed by F4/80*<sup>+</sup>* cells (Figure 1D,E and Supplementary Figure S1), and their increase also correlated with the advanced stages of the infection (after 15 dpi). The expression of HO-1 in F4/80*<sup>+</sup>* cells slightly increased after 1 dpi, while it considerably increased during the infection (Figure 1F). On the other hand, the production of ROS/RNS was significantly increased only at 1 dpi, and decreased during infection (Figure 1G), suggesting that the expression of HO-1 in peritoneal F4/80*<sup>+</sup>* cells inversely correlated with the production of ROS/RNS. In order to provide more evidence in this regard, we incubated RAW 264.7 macrophages with parasite components (FhTE) in the presence of CoPP or SnPP, and analyzed the production of ROS/RNS by these cells. FhTE slightly increased the production of ROS/RNS, while CoPP and SnPP significantly decreased and increased the production of ROS/RNS by FhTEtreated macrophages, respectively (Figure 1H). Of note, FhTE *per se* induced ROS/RNS expression, which could be the result of an active respiratory burst, such as that seen in F4/80+ cells from PECs of infected mice at 1 dpi (Figure 1G). Altogether, these results might indicate that *F. hepatica* induces the expression of HO-1 in F4/80*<sup>+</sup>* cells recruited to the peritoneum, inhibiting ROS/RNS production during the course of the infection.
