Thymic medulla

Medulla thymi

Lymphatic & immuneLymphaticsThoraxLeft and right

View left in 3D View right in 3D

What it is

The paler inner zone of each thymic lobule, surrounded by the dark, lymphocyte-packed cortex. It holds mature T cells, epithelial cells and Hassall's corpuscles, whorled keratinised bodies found nowhere else.

Function

Site of negative selection: T cells that react against the body's own proteins are deleted here before release into the blood.

Size

Each lobule 0.5-2 mm across; the medulla is continuous from lobule to lobule

Clinical note

Medullary epithelial cells use the AIRE gene to display tissue-specific proteins (insulin, thyroglobulin...) to developing T cells; AIRE mutations cause autoimmune polyendocrine syndrome type 1.