The mouse T-lymphocyte-activating molecule THAM is associated to ECTO-aminopeptidase activity

In the mouse there are three non-CD3/T-cell receptor T cell-activating molecules, Thy-1, Ly-6 antigens, and the CD28 homologue. Using a mitogenic rat monoclonal antibody, we identified a novel thymocyte-activating molecule (THAM). Here we review the main characteristics of this heterodimeric glycoprotein with respect to its expression on lymphoid and non-lymphoid cells, and its biochemical and T-cell-activating properties. THAM shares a number of structural features with surface peptidases of epithelial cell brush borders, and is in fact associated with a neutral aminopeptidase activity. The biologic significance of this observation is discussed in the context of recent data on the involvement of several ecto-enzymes in T-cell activation and differentiation.