The dynamic behaviour of Hassall's corpuscles and the transport of particulate matter in the thymus of the guinea-pig.

Young immature guinea-pigs, 7–10 weeks old, were exposed to X-rays directed solely to the thymus gland which received a tissue dose of 300 r. An equal number of animals were not irradiated. All the animals had an intracardiac injection of 0.3 ml of Indian ink containing 10 per cent carbon of uniform particle diameter. An increase in number and size of Hassall's corpuscles was noted in irradiated thymus glands. Simultaneously, there was an increase in the uptake of carbon in the walls of blood vessels and in perivascular macrophages. Within 12 hours of irradiation Hassall's corpuscles contained carbon, at first in a finely stippled form in polymorphonuclear leucocytes and, later, in larger aggregates in macrophages. After an interval of 14 days Hassall's corpuscles disappeared and the lobules were re-populated with thymocytes. Migration outwards of carbon laden macrophages occurred between the 14th and 21st days. By contrast the entry of carbon in control glands took place more slowly but retention of particulate matter in Hassall's corpuscles was still present at the end of the experimental period of 56 days. It is suggested that Hassall's corpuscles are a `graveyard' for dead thymocytes, possibly for some effete circulating lymphocytes and in some circumstances for polymorphonuclear leucocytes. It is also suggested that antigens localize in Hassall's corpuscles. Furthermore, since γ-globulin is known to localize there, these antibodies may be mobilized and returned to the circulation by macrophage activity.