5'-nucleotidase activity of murine T-cell subpopulations separated according to their Lyt2 and L3T4 phenotypes.

Murine T lymphocytes were separated by "panning" into four subpopulations, according to their Lyt2 and L3T4 phenotypes: Lyt2+L3T4+, Lyt2-L3T4-, Lyt2+L3T4-, and Lyt2-L3T4+. The activity of ecto-5'-nucleotidase in each subpopulation was measured. 5'-Nucleotidase activity was undetectable in Lyt2+L3T4+ cortical cells but was expressed in medullary Lyt2-L3T4+ and Lyt2+L3T4- T lymphocytes. The small cortical subpopulation of thymocyte precursors with the Lyt2-L3T4- phenotype expressed levels of 5'-nucleotidase comparable to the levels of medullary, mature lymphocytes. These results suggest that the use of ecto-5'-nucleotidase as a marker of the degree of T-cell maturation is questionable.