Fig. 5

A Representative photomicrographs from H&E-stained lung sections showing a Control group: patent alveoli and thin interalveolar septa (arrow) lined by flat type I pneumocytes (arrow head) and cuboidal type II pneumocytes (short arrow). An alveolar capillary (c) is also seen. b Covid group: Extensive consolidation (double arrow) with obliterated alveolar lumens, thickened interalveolar septa, inflammatory cellular infiltration (if), and intra alveolar hemorrhage (asterisk). c MSCs-EVs group: with patent alveolar lumens and thin interalveolar septa (arrow) and residual area of consolidation (double arrow) and inflammatory cellular infiltration (if). d Graph showing the lung injury scoring system. Data are expressed as mean ± SEM.***p < 0.001 versus control, ###p < 0.001 versus covid group. B Representative photomicrographs from Masson trichrome stained lung sections showing a) Control group: with fine collagen fibers in the interalveolar septa (arrow). b Covid group: with abundant, intensely staining collagen fibers surrounding the bronchioles (arrowhead) and in the extensively consolidated lung tissue (curved arrow). c MSCs-EVs group: with fine, intensely stained collagen fibers in the thin interalveolar septa (arrow). d Graph showing collagen fiber mean area percentage in the experimental groups (Masson’s trichrome-stained sections). Data are expressed as mean ± SEM.***p < 0.001 versus control, ###p < 0.001 versus covid group