Epithelial reticular cell
Epithelial reticular cells (or epithelioreticular cells) are a structure in both the cortex and medulla of the thymus. However, histologically, they are more easily identified in the medulla. These cells contain secretory granules which are thought to contain the thymic hormones.
There are six different types: Types 1-3 are in the cortex, and types 4-6 are in the medulla.
Epithelial reticular cells are the primary cell involved with making sure that no T cells are allowed to survive that will attack the body's own cells. It does this by expressing a very large proportion of its genome, and expressing as many 'self' proteins on its cell membrane as possible. As the T cells migrate from the cortex of the thymus to the medulla, they come into contact with many epithelial reticular cells, and if they recognise self proteins as a pathogen, then the epithelial cells destroy them.