RESUMEN
SARS-CoV-2 enters the respiratory tract where it infects the alveoli epithelial lining. However, patients have sequelae that extend well beyond the alveoli into the pulmonary vasculature and perhaps beyond to brain and other organs. Because of the dynamic events within blood vessels, histology fails to report on platelet and neutrophil dynamics. Because of the rapid non-transcriptional behaviour of these cells neither single-cell RNAseq nor proteomics report robustly on their critical behaviours. We used intravital-microscopy in level-3 containment to examine the pathogenesis of SARS-CoV-2 within three organs in mice expressing human-ACE-2 ubiquitously (CAG-AC-70) or on epithelium (K18-promoter). Using a neon-green-SARS-CoV-2, we observed both epithelium and endothelium infected in AC70 mice but only the epithelium in K18 mice. There was increased neutrophils in the microcirculation but not in the alveoli of the AC70 lungs. Platelets formed large aggregates in the pulmonary capillaries. Despite only neurons being infected within the brain, profound neutrophil adhesion forming the nidus of large platelet aggregates were observed in the brain microcirculation with many non-perfused microvessels. Neutrophils were seen breaching the brain endothelial layer associated with a significant disruption of the blood-brain-barrier. Despite ubiquitous ACE-2 expression, CAG-AC-70 mice had very small increases in blood cytokine, no increase in thrombin, no infected circulating cells and no liver involvement suggesting limited systemic effects. In summary, our imaging of SARS-CoV-2-infected mice gave direct evidence that there is a significant perturbation locally in the lung and brain microcirculation induced by local viral infection leading to increased inflammation and thrombosis in these organs.