IL-9 strengthens the survival and protumor effect of mast cells in tumor microenvironment.

<p>(A and B) Mast cells upregulated the expressions of IL-9 by Treg cells. BMMCs were injected into tumor-bearing mice with IL-17 antibody or control antibody. Seven days later, the tumor-infiltrating Treg cells were isolated for the analysis of IL-9 by real time RT-PCR (A). Or the isolated Treg cells were cultured for 48 hours. The supernatant was used for IL-9 ELISA assay (B). (C and D) The interference of IL-9 signaling affected mast cell-mediated MDSC infiltration and mast cell-promoted tumor growth. 5×10⁶ BMMCs were injected into tumor-bearing mice (n = 6) by i.v. injection. IL-9 neutralizing antibody or CD25 depleting antibody was i.p. injected to the mice 1 h, 2 days and 5 days after BMMCs injection. On day 12, the tumor-infiltrating lymphocytes were used to analyze Gr-1⁺CD11b⁺ MDSCs by flow cytometry (C), and the tumor growth was monitored by measuring the length (L) and width (W) of tumors. The volume (V) of the tumor was calculated by the formula V = (L×W2)/2 (D). (E) IL-9 affected the survival of mast cells in tumor microenvironment. 1×10⁶ CFSE-labeled BMMCs were directly injected into tumor tissue with multiple injection sites. IL-9 neutralizing antibody was i.p. injected to the mice 1 h, 2 days and 5 days after BMMCs injection. The tumor tissues were surgically excised on day 7 for fluorescent analysis of frozen sections.