Immunohistochemical studies in human thymomas

Forty five human thymomas were studied immunohistochemically using antibodies to thymosin a-1, thymosinβ-3, cortical epithelium of human thymus (UH-1), mouse thymic nurse cells (Th-3) and Leu-7. Most thymomas were found to contain thymosin α-1 (80%) and thymosinβ-3 (89%). Also used in the study were a new monoclonal antibody (UH-1), which reacts with the epithelial cells forming a meshwork in the cortex of the normal newborn thymus and Leu 7, which reacts with subcapsular epithelial cells in the outer thymic cortex. The combined use of UH-1 and Leu-7 was found to identify neoplastic epithelial cells of thymic cortical origin in thymomas. Approximately 80% (37/45) of the thymomas in the present study reacted with Leu-7, UH-1 or both antibodies, and were thus considered to be derived from cortical thymic epithelium. Of the eight thymomas which were negative with both Leu-7 and UH-1, four were histologically of the mixed type characterized by the formation of epithelial cell islands. All four of these thymomas were positive with thymosin and were therefore considered to be of medullary origin. Ten of the thymoma were associated with myasthenia gravis; all were positive with UH-1 and were considered to be of cortical origin.