Tumor cell–derived SCF is responsible for the infiltration of mast cells into tumor. (A) Assay of SCF expression in H22 tumor or tumor cells. SCF expression was detected by RT-PCR and Western blot, respectively. SCF in the supernatants of the cultured tumor tissue or tumor cells was assayed by ELISA. Mouse monocyte system cell line RAW246.7 was used as the negative control. (B) Assay of SCF expression in tumor cells and tumor tissues. SCF expression in murine tumor cell lines and human tumor cell lines, corresponding murine tumor and specimens from human tumor, and normal tissue adjacent to tumor was detected by RT-PCR and Western blot, respectively. (C) SCF on the surface of different tumor cells was analyzed by flow cytometry. (D) Assay of soluble SCF produced by different tumors. Tumor cell lines, the corresponding tumor tissues, and the adjacent tissues around the tumor were cultured in vitro. SCF in the supernatants was detected by ELISA. (E) Silence of SCF expression in H22 tumor cells by SCF siRNA. SCF expression was detected by RT-PCR and Western blot, respectively. The soluble SCF released from tumor tissue was assayed by ELISA. (F) SCF-knockdown tumor cannot efficiently induce the migration of MCs. SCF-knockdown or control tumor tissues were used for transwell assay of MC migration (left). The infiltration of circulating MCs into SCF-knockdown or control tumor tissue (right) was analyzed using the same protocol as that in Figure 1B. *P < .05, compared with control tumor. Error bars represent SD.