T cells (IMAGE) University of Basel Caption If the upper threshold density of T cells is reached, cell death is initiated. Credit Biozentrum, University of Basel Usage Restrictions Only to be used in reporting on the related press release. 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.