Chromium 51 51cr

The spleens were collected and processed into single‐cell suspensions. NK cells were isolated from splenocytes to >90% purity, starting with cells from two pooled spleens, using the EasySep Mouse NK Cell Isolation Kit (Stemcell Technologies, Vancouver, CA) following the manufacturer's instructions. Target YAC‐1 cells were labeled with 100 μCi of Chromium‐51 (⁵¹Cr; Perkin Elmer, Waltham, MA, USA) for 75 min. A total of 10 000 labeled target cells were added to the wells of V‐bottomed plates, followed by effector NK cells at various effector‐to‐target ratios. Spontaneous ⁵¹Cr release was determined in YAC‐1 cultures (six wells) incubated in the medium alone. Hydrochloric acid (1 M) was added to three wells to maximize ⁵¹Cr release. After 4 h of incubation at 37°C and 5% CO₂, supernatants were collected and ⁵¹Cr release was measured on the Wallac Wizard gamma Counter (Perkin Elmer, Waltham, MA, USA). We determined the percentage of labeled target cells that were lysed specifically by NK cells with the following formula: $$\text{Specific lysis}=\left[\left(\text{experimental release}–\text{spontaneous release}\right)/\left(\text{maximum release}–\text{spontaneous release}\right)\right]\times 100.$$