Surface expression of adenosine deaminase in mitogen-stimulated lymphocytes

Adenosine deaminase (ADA) expression on the surface of mitogen-stimulated lymphocytes was studied by flow cytometry. The gate for lymphocytes was located by cell size (forward scatter), cytoplasmic complexity (side scatter) and by expression of the markers CD2, CD4, CD8 and CD19. After mitogenic proliferation two populations appeared, one corresponding to non-stimulated cells, and the other consisting of larger cells which showed relatively high expression of adenosine deaminase on their surface. The increase was similar to that observed for CD71 expression, and paralleled the increase in 3H-thymidine incorporation. There was a correlation between ADA and CD71 expression (r = 0.92 for phytohaemagglutinin (PHA) and 0.97 for pokeweed mitogen (PWM)). These results suggest a role for ecto-adenosine deaminase in lymphocyte proliferation and/or triggering.