Medulla region of human thymus (IMAGE) The Francis Crick Institute Caption The medulla region of a human thymus from a 1-year-old patient, showing epithelial cells (cyan and yellow), fibronectin, a protein of the extracellular matrix (magenta), and Polykeratin stem cells are those positive for all the three colours. Credit 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.