The virus begins destroying lung tissue 60 hours after infection. In the new study, researchers used "Mini-lungs" grown from tissue donated to gather important insights into how COVID-19 damages the lungs. Researchers were able to describe the machanisms underlying SARS-CoV-2 infection and the early innate immune response in the lungs. Researchers extracted from the donated tissue a type of lung cell known as albeolar type 2 cells. They then reprogramed these cells back to their earlier "stem cell" stage.
They were able to grow self-organizing alveolar like 3D structures that mimic the behavior of key lung tissue. This approach has allowed researchers to grow 3D "Mini-lungs" in the lab and stud what happens when they become infected with SARS-CoV-2. The team infected the organoids with a strain of SARS-CoV-2 . Using a combination of fluorescence imaging and single cell genetic analysis they were able to study how the cell responded to the virus.
When the 3D models were exposed to SARS-CoV-2 , the virus began to replicate rapidly. The virus reached full cellular infection just 6 hours after infection. Around the same time, the cells began to produce interferous. Interferons are proteins that act as warning signals to neighboring cells. They tell cells to activate their antiviral defenses.
After 48 hours, the interferons triggered the innate immune response. This is the first line of defense that triggers cells to fight back 60 hours after infection a subset of aveolar cells began to disintegrate leading to cell death and damage to the lung tissue. Researchers observed changes to lung cells during the 3 days of infection. But clinical symptons of COVID-19 rarely occurs so quickly and come sometimes take more than 10 days after exposure to appear.
Researchers said there several possible reasons for this. It may take several days for virus to infiltrate from upper respiratory tract to the lungs alveoli. It may also require a greater proportion of alveolar cells to be infected before a patient displays symptoms of COVID-19.