Human lung fibroblasts express interleukin-6 in response to signaling after mast cell contact

Asthma is a chronic inflammatory disease of the airways. Mast cell-derived cytokines may mediate both airway inflammation and remodeling. It has also been shown that fibroblasts can be the source of proinflammatory cytokines. In the human airways, mast cell-fibroblast interactions may have pivotal effects on modulating inflammation. To study this further, we cocultured normal human lung fibroblasts (NHLF) with a human mast cell line (HMC-1) and assayed for production of interleukin (IL)-6, an important proinflammatory cytokine. When cultured together, NHLF/HMC-1 contact induced IL-6 secretion. Separation of HMC-1 and NHLF cells by a porous membrane inhibited this induction. HMC-1-derived cellular membranes caused an increase in IL-6 production in NHLF. Activation of p38 MAPK was also seen in cocultures by Western blot, whereas IL-6 production in cocultures was significantly inhibited by the p38 inhibitor SB203580. IL-6 production in cocultures was minimally inhibited by a chemical inhibitor of nuclear factor-kappaB (Bay11), indicating that nuclear factor-kappaB may have a minimal role in signaling IL-6 production in mast cell/fibroblasts cocultures. Blockade of inter-cellular adhesion molecule-1, tumor necrosis factor-RI, and surface IL-1beta with neutralizing antibodies failed to significantly decrease IL-6 production in our coculture, indicating that other receptor-ligand associations may be responsible for this activation. These novel studies reveal the importance of cell-cell interactions in the complex milieu of airway inflammation.