MSCs alter IL-2–induced upregulation of activating NK receptors. Expression of NKp46, NKp30, NKp44, CD69, and NKG2D on freshly isolated NK cells derived from a representative donor and on the same NK cells after 6-day culture in IL-2 in the presence or in the absence of MSCs. Cells were analyzed by gating on CD56⁺ lymphocytes. Gray profiles represent expression of activating receptors; open histograms represent negative control. Numbers indicate percentages of positive cells; numbers in parentheses represent MFI.