A fine structure study of human thymus.

A study of the fine structure of human thymus, including normal hyperplastic and with thymoma, is reported in this paper. There is increasing experimental evidence that thymic epithelial cells are a source of hormone. It is, therefore, of interest that we found epithelial cells containing intravesicular cytoplasmic material that reacted with silver methenamine as do mucoproteins. Similar material, possibly extracellular, was seen in close contact with lymphocytes and macrophages in the thymus. The results suggest a possible mechanism for epithelial cell/lymphocyte interaction. Some epithelial cells also showed phagocytic features and all appear to play a structural role. The presence of nuclear pockets was noted within lymphocyte nuclei.