ADA plays an important role in the development of the immune system and the enzyme is probably associated with T-lymphocyte differentiation. ADA has been shown to exist in different molecular weight forms. In man the major forms are the red cell ADA or ADA-S and the tissue specific ADA or ADA-L. ADA-S can be converted to ADA-L by complexing with ADCP. Intact human peripheral T lymphocytes and human thymocytes were first incubated with rabbit anti-ADA and anti-ADCP antisera, followed by incubation with FITC-labeled swine anti-rabbit IgG. Since only cell surface ADA and ADCP would be exposed to the antisera, fluorescence indicates ADA and ADCP expression on the outer cell membrane.
Labeled cells were analyzed by fluorescence microscopy and FACS analysis. ADCP is present at the cell membrane of about 50% of the T lymphocytes; 10-20% of the cells contain membrane-bound ADA. When these cells were incubated with a lysate of human erythrocytes (as source of ADA-S) about 50% of the cells were found to display ADA at the membrane. Human thymocyte suspensions contained 20-30% membrane-ADA positive cells and 10-20% membrane-ADCP positive cells. The physiological significance of ADA and ADCP expression at the extracellular surface of human T-lymphoid cells will be resolved.
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Dinjens, W., Boon, J., Ten Kate, J. et al. IMMUNOHISTOCHEMICAL DEMONSTRATION OF ADA AND ADCP ON THE CELL SURFACE OF HUMAN T-LYMPHOID CELLS: 54. Pediatr Res 19, 752 (1985). https://doi.org/10.1203/00006450-198507000-00074