Hassall's corpuscle in thymus (human, puberty)

Stain: Hematoxylin. A larger magnification of the thymic medulla reveals the purple-stained structures in the centre of a so-called Hassall's (or thymic) corpuscle consisting of keratinized (*) epithelial cells. It is surrounded by recognizable flattened cells showing keratohyalin granules (-->). The outer shell consist of more layers of close packed concentrically arranged cells with light-stained nuclei characteristic for these specialized epithelioreticular cells. (1) lymphocytes with small dark nuclei. (2) reticular (dendritic) cell type with distinct nucleolus.