RÉSUMÉ
<p><b>OBJECTIVE</b>To characterize the phenotypic and biological properties of CD56(+) natural killer cells from human peripheral blood mononuclear cells (PBMCs).</p><p><b>METHODS</b>Surface markers and intracellular cytotoxic molecules were stained with multi-color-labeled monoclonal antibodies and analyzed at the single cell level the relation between NK subsets and biological characteristics by flow cytometry.</p><p><b>RESULTS</b>NK cells in PBMCs could be divided into two major populations, CD56(bright) and CD56(dim), based upon the expression of CD56 molecules. Both CD56(bright) and CD56(dim) expressed CD95 (Fas) with CD95(bright) and CD95(dim) subsets. CD56(dim) subsets had higher percentage of CD8, granzyme B and perforin expression compared to those of CD56(bright) subsets. In CD56(bright) and CD56(dim) subpopulations, CD95(bright) and CD8(+) subsets had higher percentage of granzyme B and perforin expression.</p><p><b>CONCLUSION</b>CD56(+) NK cells in PBMCs are composed of distinct subpopulations, CD56(dim) and CD56(dim) CD8(+) NK subsets have higher percentage of granzyme B and perforin and may play an important role in the killing of target cells.</p>