Whole section of human thymus (IMAGE) The Francis Crick Institute Caption Whole section of a human thymus from a few-months-old patient. Polykeratin stem cells are sparsely located, expressing marker genes in red, white and green. Credit Mary Green and Roberta Ragazzini, the Francis Crick Institute, Developmental Cell. Usage Restrictions Only use with this press release and 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.