The ultrastructure of the normal human thymus: A study of 36 cases

Electron microscopy of the normal human thymus demonstrates a supporting framework of epithelial‐reticular cells with long branching cytoplasmic processes joined by desmosomes. In the interstices of the epithelial‐reticular cell processes lie lymphocytes, macrophages, and rare myoid cells. Both small and large lymphocytes are evident. No desmosomes are observed between the lymphocytes and the epithelial‐reticular cells. Macrophages are most numerous in the cortex where they often contain phagocytized nuclear debris. The possible functional significance of the above‐described fine structural features is discussed.