T cell expresses PD-1 (IMAGE) University of California - San Diego Caption A 3-D image shows a T cell expressing the immune checkpoint receptor PD-1 (green) interacting with an antigen presenting cell expressing the ligand PD-L1 (magenta). Credit Hui Lab, UC San Diego Usage Restrictions Must be used in conjunction with Science Immunology paper on PD-1 research. 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.