S-100 immunoreactive interdigitating cells in normal and in Down's syndrome human thymuses.

The present research deals with the localization of the interdigitating cells (IDCs) in normal and in Down's human thymuses. Eight thymic biopsy samples of normal children from 16 months to 10 1/2 years and six samples of Down's children from 2 months to 6 1/2 years were stained by the indirect immuno-peroxidase method using an anti-S-100 protein serum. IDCs are localized in the medullary zones, always numerous in all the Down's thymuses and in an age-related decreasing number in normal thymuses. The interrelationships between the physiological and pathological role of IDCs in inducing self-tolerance and T-cell activation and the numerical distribution in normal and in Down's human thymuses are discussed.