ACTIVATION OF CORD T-LYMPHOCYTES .4. ANALYSIS OF SURFACE EXPRESSION AND FUNCTIONAL-ROLE OF 1F7 (CD26) MOLECULE

A role for CD26 surface antigen (Ag) in both CD3- and CD2-mediated T c ell activation has been previously demonstrated. To analyze the functi onal role of CD26 in the CD3- and CD2-induced activation pathways of c ord T cells, which represent the most reliable source of Ag-unprimed T cells, eve employed a newly developed anti-CD26 monoclonal antibody, termed anti-1F7, which is able to modulate the molecule on the cell me mbrane and synergize with anti-CD3 and anti-CD2 in activating T lympho cytes. The results showed that CD26 Ag is expressed on the surface of almost all resting cord T cells and that its fluorescence intensity is enhanced by activation. The binding of anti-1F7 induced a decrease in CD26 membrane expression, with no detectable effect on the surface ex pression of other cord T cell-related molecules. Moreover, the modulat ion of CD26 resulted in an increase in anti-CD3-mediated cord T cell a ctivation through an enhancement in intracellular calcium levels, IL-2 receptor expression, and IL-2 synthesis, whereas it had no effect on cord T cell activation induced by anti-CD2 or anti-CD2 plus exogenous IL-2. The fact that the selective involvement of CD26 in the activatio n pathway triggered by anti-CD3, but not anti-CD2, could be reversed b y prior stimulation of cord T cells with anti-CD3 suggests that this f unctional feature, which resembles that of mature thymocytes, may be l inked to the Ag-unprimed cell phenotype of cord T lymphocytes. (C) 199 4 Academic Press, Inc.