IL-15 is not directly chemotactic but induces expression of molecules associated with leukocyte trafficking. (A) SD-1 cells were placed in the top section of a bare filter transwell (5 μM pore size) and exposed to IL-15 (1, 10, 100, 300, or 1000 ng/mL) in the bottom section of the transwell. Transmigration was assessed following a 3-hour incubation period. The migration index was calculated by counting the total number of cells transmigrated in response to IL-15 as a proportion of the total number of cells that transmigrated in response to chemotaxis buffer alone (spontaneous migration). Data shown are from 1 experiment performed in triplicate. (B) SD-1 cells (n = 3 independent cultures) were treated with IL-15 (25 ng/mL) for 72 hours and levels of mRNA encoding PSGL-1 and CXCR3 measured by qPCR. Results are expressed as relative quantities with the level in media alone arbitrarily set to 1.0. (C) SD-1 cells (n = 3 independent cultures) were treated as in panel B, and the surface expression of PSGL-1 and CXCR3 was analyzed by fluorescence-activated cell sorter. Corrected mean fluorescence intensity (cMFI) represents MFI-specific antibody − MFI isotype control. (D) Following IL-15 treatment as in panel B above, expression of 95 genes associated with tumor metastasis was assessed using a commercially available RT2 PCR profiler array. Data are represented as a scatterplot (relative quantification log10), and solid lines represent twofold down- or upregulation. The 7 genes showing >twofold change with IL-15 treatment are listed. (E) Validation of hits from panel D by qPCR of SD-1 cells (n = 3 independent cultures) treated with media ±IL-15 (25 ng/ml) for 72 hours confirmed modest upregulation of Serpine1 by IL-15. Data show the number of copies of Serpine1 per 1000 copies of the housekeeping control gene TBP. All data are mean ± standard error of the mean and were analyzed by unpaired Student t tests. *P < .05, **P < .01, ***P < .001.
