Based on this age-classified analysis, we defined the following disease stages to describe the progression of PF in Ifngr1-/-Rag2-/- mice: (i) intact phase (<10 weeks old), (ii) inflammatory phase (10–20-week-old, characterized by inflammatory cell infiltration in the BALF and mild to moderate collagen deposition in the lungs), and (iii) fibrotic phase (>20 weeks old, characterized by severe collagen deposition in the lungs) (Fig. 1g). Here, IFNGR1 is linked to pemphigus foliaceus.