Intercellular interactions between mast cells and fibroblasts promote pro-inflammatory signaling

The mechanisms that mediate acute exacerbations in chronic inflammatory diseases are not understood. As IL-8 is a potent chemoattractant for neutrophils in acute inflammatory lesions, we investigated the role of fibroblast-mast cell interactions in short-term IL-8 release. Human gingival fibroblasts were co-cultured with human mast cells (HMC). The concentration of IL-8 in co-culture medium was measured by ELISA. HMC-fibroblast co-cultures showed >8-fold higher IL-8 secretion than fibroblasts or HMC alone. Increased IL-8 secretion required HMC-fibroblast intercellular contact, was enhanced by serum and was blocked by the gap junction inhibitor β-glycyrrhetinic. Calcein-dye transfer showed intercellular, gap junction communication between HMC and fibroblasts that was dependent in part on hyaluronic acid on the cell surface of fibroblasts. IL-8 secretion by fibroblasts was strongly promoted by hyaluronic acid. Pre-treatment of HMC with thapsigargin provoked 15-fold higher IL-8 production by fibroblasts in co-cultures. Chemotaxis of mouse neutrophils was enhanced 2-fold in response to conditioned medium from HMC-fibroblast co-cultures. We conclude that mast cells adhere to fibroblasts and promote IL-8 secretion, which enhances neutrophil chemotaxis and the inflammatory response.