Mesenchymal stem cells and their derived exosomes for the treatment of COVID-19

Table 2 Coronavirus disease 2019 causes primary pathological changes

Organ system	Primary change
Lung tissue	Acute interstitial pneumonia occurs along with diffuse alveolar damage. The lung tissue shows macrophage infiltration, hyaline membrane formation, and alveolar wall edema. Microvascular involvement includes hyaline thrombosis, hemorrhage, vascular endothelial edema, and immune cell infiltration[134]	+
Cardiovascular system	Degeneration and necrosis of some cardiomyocytes, interstitial congestion and oedema, and infiltration by a few monocytes, lymphocytes, and neutrophils are observed. The nucleic acid test for novel coronavirus is occasionally positive. Endothelial cell detachment and endothelial or whole-layer inflammation are present in small blood vessels in significant parts of the body, accompanied by mixed intravascular thrombosis, thromboembolism, and infarction in the corresponding areas. The microvessels of major organs are prone to hyaline thrombosis[135]	+
Liver	The liver is enlarged with dark red hepatocyte degeneration and focal necrosis with neutrophil infiltration; hepatic sinusoids are congested, and lymphocyte and monocyte infiltration and microthrombosis are observed in the confluent area[136]	+
Gallbladder	The gallbladder is highly filled, and the mucosal epithelium is detached[137]	+
Kidney	The renal glomeruli exhibit congestion and occasional segmental fibrinoid necrosis; proteinaceous exudates can be observed within the glomerular lumens. Proximal renal tubular epithelial degeneration, partial necrosis, and desquamation are present, while casts can be found in the distal tubules. The renal interstitium is congested, with microthrombi formation noted[138]	+
Brain	Congestion, oedema, degeneration of some neurons, ischaemic changes and detachment, phagocytosis, and satellite phenomena are found. Infiltration of monocytes and lymphocytes in the perivascular space is observed[139]
Testicle	Varying degrees of reduction in the number of spermatogenic cells and degeneration of Sertoli and Leydig cells are observed[140]	+
Adrenal gland	Cortical cell degeneration, focal hemorrhage, and necrosis are observed[141]
Esophageal, gastric, and intestinal mucosal epithelium	There is variable degeneration, necrosis, and detachment observed, accompanied by the infiltration of monocytes and lymphocytes in the lamina propria and submucosa[142,143]	+

+: The nucleic acid test for novel coronavirus was positive.