PROMOTION OF MOUSE FIBROBLAST PROLIFERATION BY IGE-DEPENDENT ACTIVATION OF MOUSE MAST-CELLS - ROLE FOR MAST-CELL TUMOR-NECROSIS-FACTOR-ALPHA AND TRANSFORMING GROWTH-FACTOR-BETA-1

Pathologic fibroblast proliferation or tissue fibrosis develops in cer tain chronic allergic diseases and in a wide array of other inflammato ry disorders in which mast cell activation is also a prominent feature . In this study we investigated a number of potential mechanisms by wh ich IgE-dependent activation of mouse mast cells might influence the p roliferation of mouse fibroblasts in vitro. We found that supernatants from in vitro-derived mast cells that had been activated by IgE and s pecific antigen (but not those from quiescent mast cells) promoted the proliferation of mouse embryonic skin or 3T3 fibroblasts, and we show ed that this effect was detectable in the absence of fetal calf serum. We analyzed the kinetics with which the fibroblast-proliferative acti vity was secreted from bone marrow-derived cultured mast cells and fou nd that it was released both rapidly (i.e., in 30 minutes or less) and for a more prolonged period (i.e., for more than 2 hours) after IgE-d ependent mast cell activation. We then measured the levels at which th e mast cells produce a number of cytokines that are known to affect fi broblasts (IL-1, IL-6, transforming growth factor-beta 1 [TGF-beta 1], and tumor necrosis factor-alpha [TNF-alpha]) and assessed their relat ive effects, as recombinant cytokines, on fibroblast proliferation. Ou r mast cells secreted high levels of TGF-beta 1 and TNF-alpha, interme diate amounts of IL-6, and low levels of IL-1. We titrated the fibropr oliferative effects of each of these cytokines and determined that at a dose of 50 pg/ml their rank order of activity was TGF-beta 1 > TNF-a lpha > IL-1 > IL-6, with all but IL-6 having significant effects. The ability of supernatants from activated bone marrow-derived cultured ma st cells to promote fibroblast proliferation was partially diminished by absorption with neutralizing antibodies against either TNF-alpha or TGF-beta 1, and absorption of the supernatants with a combination of antibodies against TNF-alpha and TGF-beta 1 reduced their ability to i nduce fibroblast proliferation by approximately 50% (p less than or eq ual to 0.001, n = 5). These findings show that IgE-dependent activatio n of mouse mast cells can result in the release of mediators that prom ote fibroblast proliferation in the absence of any other cell type and suggest that mast cell-derived TNF-alpha and TGF-beta 1 contribute su bstantially to this effect. They also suggest that these cytokines exe rt their effects through synergistic interactions with other mast cell mediators.