Macrophages in lungs (IMAGE) Texas Biomedical Research Institute Caption Using fluorescent markers, Texas Biomed researchers and colleagues identified the cell populations active in the lung in the first few days of COVID-19 infection. Under the microscope, they observed immune cells called macrophages (the large multicolored circles) responding to SARS-CoV-2 infection, at three days following infection (center). These macrophages were not present in the lung before infection (left) and most were no longer detected two weeks after infection (right). Blue spots are nuclei of normal lung cells. Credit Texas Biomed Usage Restrictions Can be reused with credit. License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.