ULTRASTRUCTURAL LOCALIZATION OF 5'-NUCLEOTIDASE IN MOUSE THYMIC CORTEX / 解剖学报

ABSTRACT

The thymic cortex is the important site for thymocyte differentiation, maturation and selection. Direct cell-cell interactions between thymocytes and distinct stromal cells are an important pattern to demonstrate the essential role in T-cell development. In order to approach the mechanism of their interactions, ultrastructural cytochemical localization of 5'-nucleotidase activity in the thymic cortex of BALB/c mice were investigated by means of Robinson and Karnovsky method using 5'-AMP or 5'-IMP as the substrate, cerium as the capture agent, and levamisol (an inhibitor of nonspecific alkaline phosphatase) was also used. The cytochemical distribution of the reaction products from both the 5'-AMPase and 5'-IMPase activity was essentially similar. The enzyme activity was localized on the extracellular side of the plasma membrane of the epithelial reticular cells and some thymocytes, especially on their contact faces with each other. 5'-nucleotidase activity was also found in the lysosomes of macrophages and in the vacuoles, and vesicles near the plasma membrane and some lysosomes of epithelial reticular cells. The biological significance of the 5'-nucleotidase in thymic cortex was discussed.