Hassall's corpuscles--a site of thymocyte death.

Cortical thymocytes incorporated tritiated thymidine within ½-4 hours after injection and retained decreasing amounts of the isotope for 5-7 days. In contrast with the remainder of the medulla, Hassall's corpuscles selectively included tritiated nuclear material one day after injection. Corpuscular labelling reached a maximum by the 4th day, then became fragmented and disappeared by the 7th day. It is deduced that some of the DNA generated in the cortex is transported to the medulla and disintegrates in Hassall's corpuscles. The biological significance of the apparently wasteful DNA synthesis remains unexplained.