Production of TNF-α by murine bone marrow derived mast cells activated by the bacterial fimbrial protein, FimH

Production of tumor necrosis factor alpha (TNF-alpha) 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-alpha 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-alpha (300-1200 pg/10(6) cells) over 1-3 h compared with 1800-15,000 pg/10(6) cells produced by cells triggered via IgE/ antigen. This low level of TNF-alpha production in vitro is compatible with the protective in vivo role of mast cells to produce modest amounts of TNF-alpha 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 mu M cyclosporin A whereas the FimH pathway is inhibited by only 40%. These data demonstrate that the intracellular pathway activated by FimH is dif'ferent from that activated by IgElantigen both in terms of amount of TNF-alpha produced and in sensitivity to Csk This is the first evidence that FimH activates mast cells via a pathway that is distinct from that used by IgE/antigen. (C) 1999 Academic Press.