Production of TNF-α by Murine Bone Marrow Derived Mast Cells Activated by the Bacterial Fimbrial Protein, FimH

Production of tumor necrosis factor α (TNF-α) by mast cells is an important aspect of host defense against gram negative bacteria. In order to define the intracellular pathways utilized by mast cells in this physiological, protective role, we have studied the production of TNF-α in bone marrow derived mast cells from the C3H/HeJ (LPS-insensitive) strain following exposure to bacteria expressing the fimbrial protein, FimH. Mast cells exposed to FimH produce TNF-α (300–1200 pg/106cells) over 1–3 h compared with 1800–15,000 pg/106cells produced by cells triggered via IgE/antigen. This low level of TNF-α productionin vitrois compatible with the protectivein vivorole of mast cells to produce modest amounts of TNF-α in contrast to the large amounts of mediators released during maximal activation. A second difference between the two signals is sensitivity to cyclosporin A (CsA). The IgE/antigen pathway is inhibited by 90–95% at 0.02 to 0.5 μM cyclosporin A whereas the FimH pathway is inhibited by only 40%. These data demonstrate that the intracellular pathway activated by FimH is different from that activated by IgE/antigen both in terms of amount of TNF-α produced and in sensitivity to CsA. This is the first evidence that FimH activates mast cells via a pathway that is distinct from that used by IgE/antigen.