Hematoxylin and eosin staining (Fig. 6B) demonstrated that infection with the wild-type strain caused the structure of lung tissue to be severely abnormal, including: (i) loss of distinct alveolar boundaries with marked hyperplasia of alveolar epithelial cells, (ii) alveolar collapse associated with thickened alveolar walls (red arrow), (iii) luminal accumulation of inflammatory cells in bronchioles (green arrow), and (iv) dense inflammatory cell infiltration within the alveolar septa (yellow arrow), whereas the Δ-ClpX mutant group exhibited relatively intact tissues with mild lesions. Here, CLPX is linked to infection.