Exposure to TSN redirected monocytes to develop into immunosuppressive Mφ. Human monocytes were cultured for 6 days in medium alone (solid lines) or with 15% TSN from various tumor cells (dashed lines). (A and B) Expression of surface markers and production of cytokines were determined by flow cytometry and enzyme-linked immunosorbent assay, respectively. (C and D) Thereafter, the Mφ were left untreated (Med) or were stimulated with LPS or IFN-γ for 18 hours and were subsequently analyzed. (C) Results for Mφ that were exposed to TSN from U251 cells. The histograms in (A) and (C) are representative of 10 separate experiments, and the mean fluorescence intensity (MFI) values for control and TSN-treated cells (mean ± standard deviation [SD]) are indicated in Table S2. The data on cytokine production represent the mean (± standard error [SE]) of 10 experiments. Statistical differences between groups was calculated by Student t test. *P < .05 and **P < .01, compared with Mφ that were cultured in medium alone.