Decreased killing of MSCs by NK cells when MSCs were co-cultured with monocytes prior to the addition of NK cells.

<p>Monocytes were purified from PBMCs and irradiated as indicated in the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0009874#s2" target="_blank">Material and Methods</a> section. MSCs (1×10⁶ cells/plate) were cultured with the irradiated monocytes (monocyte: MSC ratio of 1∶1) for 24–48 hours before they were removed from the plates, washed and labeled with ⁵¹Cr and used as targets in the cytotoxicity assays against NK cells. The NK samples were either left untreated (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0009874#pone-0009874-g002" target="_blank"><b>Fig. 2A</b></a>) or treated with anti-CD16 mAb (3 µg/ml) (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0009874#pone-0009874-g002" target="_blank"><b>Fig. 2B</b></a>), IL-2 (1000 u/ml) (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0009874#pone-0009874-g002" target="_blank"><b>Fig. 2C</b></a>), or a combination of IL-2 (1000 u/ml) and anti-CD16 mAb (3 µg/ml) (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0009874#pone-0009874-g002" target="_blank"><b>Fig. 2D</b></a>) for 24–48 hours before they were added to ⁵¹Cr labeled MSCs at different effector to target (E:T) ratios. Supernatants were removed after 4 hours of incubation and the released radioactivity counted by a γ counter. % cytotoxicity was determined as indicated in the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0009874#s2" target="_blank">Material and Methods</a> section. One of three representative experiments is shown in this figure.