Phenotypic characterization of human CD19⁺ B cells relative to CD4⁺CD39⁺ and CD4⁺CD73⁺ T cells. Freshly isolated PBMC were stained for flow cytometry and examined for surface expression of ectonucleotidases, CD39 and CD73, ADO deaminase–associated protein, CD26, and CD25. (A) Representative expression data for CD4⁺ T and CD19⁺ B cells of a normal donor. (B) Percentages of positive cells in each cell subset shown as means ± SD for 6 different normal donors tested. B cells are CD39⁺ and CD73⁺ but negative for CD26.