SCF/c-Kit signal activates mast cells to exacerbate the immunosuppression in tumor microenvironment. When tumor size reached approximately 5 × 5 mm2, the mice bearing WT H22 tumor received the intravenous injection of mast cells (MCs) and anti–c-Kit antibody as indicated, and the mice bearing SCF-knockdown tumor received the intratumor injection of MCs. (A) The expression of Foxp3 and cytokine genes in tumor. The levels of Foxp3, IL-10, TGF-β, and IL-2 mRNAs in tumor tissues were detected by real-time PCR 72 hours after the injection of mast cells. (B) Treg cells (Foxp3+) in T cells (gated CD3+ cells) from tumor were analyzed by flow cytometry. Numbers on plots are percentages of total cells gated. (C,D) Mast cells intensify the suppression of T cells and NK cells in tumor. Seventy-two hours after the injection of mast cells, T cells and NK cells were isolated from the tumor. The proliferation of T cells (C) and the production of IFN-γ by NK cells (D) were determined as described in “Assay of soluble SCF and IFN-γ by enzyme-linked immunosorbent assay.” T cells and NK cells isolated from normal spleen were used as control. *P < .05, compared with WT tumor control. Error bars represent SD.
