Figure 1: Schedule of the interaction between MSC and NKcells. MSC inhibit NK cell proliferation upon IFN-γ activation via amongst others IDO activity and PGE-2 secretion. IL2/IL15 activated NK cells upregulate granzyme and perforin expression and can lyse allogenic as well as autologous MSC. Lysis depends on the balanced expression of activating and inhibitory NK cell receptor ligands on MSC. Serpin-B9on MSC can inhibit the granzyme activity and there by protects MSC from NK cell lysis. Abbreviations: IDO: Indolamine2,3-Dioxygenase; KIR: killer Cell Immunoglobulin-like Receptor; MICA: MHC class I Polypeptide-related Sequence A; PGE-2: Prostaglandin-E2; PVR: Poliovirus Receptor; Serpin-B9: Serineprotease b9.