Heaton Flu (IMAGE) Duke University Caption Cells of the upper respiratory tract are where influenza virus infection occurs. Red marks basal cells, green marks ciliated cells, and blue marks cell nuclei. Credit Rebekah Dumm, Duke University Usage Restrictions None License Licensed 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.