In vitro migration assays were performed by placing bulk populations of lymphocytes containing predetermined numbers of NK cells (verified by FACs analysis) from the indicated tissues on the top insert of a 5 mm chemotaxis transwell (Fisher Scientific, Waltham, MA) in which the bottom well contained warm media alone or supplemented with 100 ng/mL IL-15c. IL-15c was generated by incubating 100 ng of IL-15 with 500 ng IL-15Ra Fcchimeric protein at 37u for 20 minutes and 4u for 10 minutes. Plates containing transwells were then incubated at 37uC with CO 2 exchange, and 90 minutes after plating, cells were harvested from bottom chambers and the percent migration of NK cells was calculated as the ratio of the number of NK cells in the bottom chamber compared to the number of NK cells determined in the input sample.