ARG1 and infection: After triggering specific M1 or M2 polarization, we observed that both ISG15+/+ and ISG15-/- BMDM presented the same levels of inducible nitric oxide synthase (iNOS) (M1 marker) and arginase-1 (Arg-1; M2 marker) protein by western blotting, independently of infection and of the presence of ISG15 (S4 Fig).