The cytoarchitecture of the human thymus detected by monoclonal antibodies.

Seven monoclonal antibodies were produced against human thymic stromal cells. The monoclonal antibodies were put into two groups depending on whether the cells they detected were keratin-positive or -negative. Demonstrated in the keratin-negative group were a granular reticular meshwork, a stellate population predominantly in the medulla, and secretory cells associated with Hassall's corpuscles. In the keratin-positive group we showed two extensive epithelial networks, a trabecular and rare medullary epithelial population, and thymus-specific epithelium restricted to the subcapsule and the medulla. A novel finding was that some of the monoclonal antibodies and also OKM1 identified keratin-negative cells within Hassall's corpuscles, which implies that there are macrophages associated with these structures. The monoclonal antibodies should prove useful for separating and classifying subpopulations of stromal cells and also for monitoring changes in the thymic architecture in different thymic pathologies.