NK Cells Kill Stem Cells Figure 3. Total monocytes or those depleted of CD16+ subsets of monocytes protect MSCs and DPSCs against NK cell mediated cytotoxicity. MSCs (Fig. 3A) or DPSCs (Fig. 3B) each at 16106 cells/plate were co-cultured with highly purified and irradiated total monocytes or CD162 subsets of monocytes at 1:1 MSCs to monocyte ratio for 24–48 hours before they were detached, washed and labeled with 51Cr and added to untreated or IL-2 (1000 u/ml) pre-treated or anti-CD16mAb (3 mg/ml) pre-treated, or a combination of IL-2 (1000 u/ml) and anti-CD16 mAb (3 mg/ml) pre-treated NK cells at different E:T ratios. NK cells were pre-treated as indicated for 24–48 hours before they were added to the co-cultures of monocytes with MSCs. After 4 hours of incubation the supernatants were removed and the released radioactivity counted by a c counter. % cytotoxicity was determined at different E:T ratio, and LU30/106 cells were calculated using the inverse of the number of effectors needed to lyse 30% of the MSCs or DPSCs X100. Both autologous and allogeneic DPSCs (Fig. 3C) at 16106 cells/plate were cultured with highly purified and irradiated PLoS ONE | www.plosone.org 5 March 2010 | Volume 5 | Issue 3 | e9874