HMGB1 increases IL-33 expression and acts as an autocrine factor in enhancing IL-33 expression in a partial TLR-4 dependent fashion during cyclic stretch.

(A) MLE-12 cells were treated with 3 μg/ml HMGB1 or control solution before 6h cyclic stretch and IL-33 production was measured by ELISA. (B) MLE-12 cells were treated with 10 μg/ml HMGB1 neutralizing antibody (2G7) or control solution before 6h cyclic stretch and IL-33 production was detected by Western blot. β-actin served as loading control. (C) MLE-12 cells transfecting with non-specific control siRNA or TLR-4-specific siRNA were treated with 3 μg/ml HMGB1 or control solution before stretch. IL-33 production in each group was measured with ELISA. **P<0.01, ***P<0.001 when compared between groups denoted by horizontal lines. Each stretching group collected at least from three wells and represented a single experiment, the bar graphs illustrate data representative of three independent experiments.