Intestinal Expression of Interleukin 9 (IL-9) Induces Mast Cell-Mediated Intestinal Permeability

RATIONALE: IL-9 is a Th2-cytokine implicated in allergic responses, but not yet investigated in gastrointestinal allergy. We hypothesize that IL-9 induces mastocytosis and increased intestinal permeability.METHODS: Intestinal permeability [mucosal to serosal paracellular flux of FITC-dextran and transcellular flux of HRP, and the inversely correlating transepithelial resistance (TER)] was measured using an Ussing Chamber system in wildtype (WT) and IL-9 intestinal transgenic (iFABP-IL-9-Tg) mice. Intestinal mast cell levels were determined by staining for chloroacetate esterase activity and serum levels of histamine and the mast cell activation marker, mouse mast cell protease-1 (mMCP-1), were measured using ELISA. To attenuate mast cell function, mice received intraperitoneal injections of 10 mg/kg cromolyn or PBS every 12 hours for 60 hours.RESULTS: Ectopic overexpression of IL-9 in the intestine was associated with intestinal mastocytosis (7.20±0.327 vs 0.68±0.075 mast cells/hpf; p<0.0001), elevated serum levels of mMCP-1 (4193±905 vs 30.5±12.0 ng/ml; p<0.02), and increased intestinal permeability (2064±482 vs 263±100 ng/ml FITC-dextran, p<0.05; 65.7±11.1 vs 6.8±2.0 ng/ml HRP, p<0.02; and 0.982±0 vs 1.473±0.054 kΩ/cm2, p<0.005) compared to WT mice. Cromolyn treatment of iFABP-IL-9-Tg mice reduced serum levels of mMCP-1 (1371±211 vs 4193±905 ng/ml, p<0.05) and histamine (169±30 vs 484±60 nM, p<0.008) compared to PBS treated mice. The reduction in mast cell mediators was associated with a significant decrease in intestinal permeability (498±31 vs 2064±482 ng/ml FITC-dextran, p<0.05; 18.4±13.0 vs 65.7±11.1 ng/ml HRP, p<0.05; and 1.56±0.27 vs 0.982±0 kΩ/cm2).CONCLUSIONS: Collectively, these data establish that IL-9 overexpression in the intestine induces increased intestinal permeability, likely by a mast cell-dependent mechanism. RATIONALE: IL-9 is a Th2-cytokine implicated in allergic responses, but not yet investigated in gastrointestinal allergy. We hypothesize that IL-9 induces mastocytosis and increased intestinal permeability. METHODS: Intestinal permeability [mucosal to serosal paracellular flux of FITC-dextran and transcellular flux of HRP, and the inversely correlating transepithelial resistance (TER)] was measured using an Ussing Chamber system in wildtype (WT) and IL-9 intestinal transgenic (iFABP-IL-9-Tg) mice. Intestinal mast cell levels were determined by staining for chloroacetate esterase activity and serum levels of histamine and the mast cell activation marker, mouse mast cell protease-1 (mMCP-1), were measured using ELISA. To attenuate mast cell function, mice received intraperitoneal injections of 10 mg/kg cromolyn or PBS every 12 hours for 60 hours. RESULTS: Ectopic overexpression of IL-9 in the intestine was associated with intestinal mastocytosis (7.20±0.327 vs 0.68±0.075 mast cells/hpf; p<0.0001), elevated serum levels of mMCP-1 (4193±905 vs 30.5±12.0 ng/ml; p<0.02), and increased intestinal permeability (2064±482 vs 263±100 ng/ml FITC-dextran, p<0.05; 65.7±11.1 vs 6.8±2.0 ng/ml HRP, p<0.02; and 0.982±0 vs 1.473±0.054 kΩ/cm2, p<0.005) compared to WT mice. Cromolyn treatment of iFABP-IL-9-Tg mice reduced serum levels of mMCP-1 (1371±211 vs 4193±905 ng/ml, p<0.05) and histamine (169±30 vs 484±60 nM, p<0.008) compared to PBS treated mice. The reduction in mast cell mediators was associated with a significant decrease in intestinal permeability (498±31 vs 2064±482 ng/ml FITC-dextran, p<0.05; 18.4±13.0 vs 65.7±11.1 ng/ml HRP, p<0.05; and 1.56±0.27 vs 0.982±0 kΩ/cm2). CONCLUSIONS: Collectively, these data establish that IL-9 overexpression in the intestine induces increased intestinal permeability, likely by a mast cell-dependent mechanism.