Blue T-Cell (IMAGE) NASA/Johnson Space Center Caption This is a scanning electron micrograph of a human T lymphocyte (also called a T-cell) from the immune system of a healthy donor. Credit NIAID Usage Restrictions NIAID 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.