Differential expression of LAMPs and ubiquitin in human thymus

Lysosome‐associated membrane proteins 1 and 2 (LAMP‐1 and LAMP‐2) are implicated in a variety of normal and pathological processes. LAMP‐2 is proposed to participate in chaperone‐mediated autophagy. Autophagy regulates T‐lymphocyte homeostasis by promoting both survival and proliferation. The biological importance of this process in the thymic gland and especially the involvement of LAMPs are far from being elucidated. The aim of the study was to examine the parallel expression of LAMPs and ubiquitin, a key molecule in autophagy, in normal human thymic glands and thymomas. The immunohistochemical expression of both markers was compared with that of cyclin D1 – an important regulator of cell cycle progression. Novel evidence for differential expression of LAMPs and ubiquitin is presented. Most Hassal's corpuscules in thymoma were negative for LAMPs, but positive in normal thymus. Both lymphocytes and epithelial cells in pathological thymus showed higher intensity for LAMP‐2 compared with LAMP‐1. In thymoma, ubiquitin was more intensively positive in these cell types compared with the normal thymus, suggesting activated autophagy in the course of this pathological state. A deregulation in cyclin D1 expression in thymoma is also reported. The functional importance of these molecules in autoghagy accompanying normal and pathological processes in the thymic gland is reviewed.