The phenotypic heterogeneity of human natural killer cells: Presence of atleast 48 different subsets in the peripheral blood

Peripheral blood natural killer (NK) cells are usually defined as a homogen eous cell population. However, NK cells show heterogeneous expression of a diversity of cell surface molecules, which might reflect the diversity of N K-cell functions. Therefore, a more specific phenotypic definition of NK ce lls is necessary. In this study, we made an inventory of phenotypic subsets that are present within the peripheral blood NK-cell population of healthy donors based on differential expression of nine cell-surface markers. Usin g three-colour flow cytometric analysis we were able to define at least 48 different CD56(+) NK-cell subsets within the peripheral blood. This phenoty pic heterogeneity appeared to be stable among healthy individuals, and was also steady within CD56(dim) and CD56(bright) NK populations, indicating a possible role for these subsets in NK-cell function or differentiation.