Our data provide definitive confirmation of the recent findings obtained in an animal model of IFN-γ-knockout (GKO) mice exposed to the particulate antigen Saccharopolyspora rectivirgula (SR) (i.e., the etiologic agent involved in the immunopathogenesis of HP reaction in the majority of our patients) [11]. Here, IFNG is linked to hypersensitivity pneumonitis.