Alveolar macrophages from patients with asbestosis showed ↑ MARCO, ARG1, and IL-10. Upon exposure to chrysotile, MARCO-/- mice had ↓ fibrosis than wild type; and alveolar macrophages from MARCO-/- mice were M1-like, but those from wild type mice showed M2 phenotypes. Here, ARG1 is linked to asbestosis.