Fig. 1

Uninfected (control) and Mycobacterium abscessus-infected murine precision-cut lung slices. a–c Uninfected PCLS cultured for 48 h show normal pulmonary histology, with empty alveolar spaces (as) and alveolar septa (S) constituted by fibrous connective tissue and congestive blood vessels. The walls of the septa are lined by type I pneumocytes (N-I) and type II pneumocytes (N-II). Some isolated macrophages are observed in the wall and in the lumen of the alveolus (M). d Uninfected PCLS (control), macrophages (M), and type I (NI) and type II (NII) pneumocytes are observed. The ZN staining is negative. e, f In PCLS infected with M. abscessus for 24 h, a chronic inflammatory reaction is observed, mainly composed by lymphocytes and foamy macrophages forming conglomerates (dotted area). g Representative photomicrograph of infected slices stained with ZN that are positive for the presence of mycobacteria; M. abscessus is found in the lumen of the alveoli (arrowheads) and intracellularly infecting the foamy macrophages (circle). H&E staining: (a–c, e, f), ZN staining: (d, g). Total magnification: ×5 (a), ×10 (b, e), ×40 (c, d, f, g)