MAST-CELL GRANULES POTENTIATE ENDOTOXIN-INDUCED INTERLEUKIN-6 PRODUCTION BY ENDOTHELIAL-CELLS

Mast cells are constituent cells of vascular tissue and their numbers are increased in atherosclerotic vessels. To gain insight into the rol e of mast cells iu vascular inflammation, the effect of mast cell gran ules (MCG) on endothelial cell production of interleukin-6 (IL-6) was examined. Human umbilical vein endothelial cells (HUVEC) were cultured with lipopolysaccharide (LPS) in the presence or absence of rat perit oneal MCG and IL-6 production was assayed by enzyme-linked immunosorbe nt assay. The interaction of MCG with HUVEC in culture was examined by electron microscopy (EM). The EM studies revealed that MCG are intern alized by HUVEC and appear intact even after 24 h in culture. Unactiva ted HUVEC produced little or no IL-6 either in the presence or absence of MCG. Treatment of HUVEC with LPS stimulated IL-6 production in a d ose- and time-dependent fashion. Addition of MCG to LPS-activated HUVE C resulted in the potentiation of IL-6 production at all LPS doses, MC G-induced enhancement of IL-6 production was evident even at a mast ce ll-to-endothelial cell ratio of 1:32. The enhancement of IL-6 producti on by MCG was also seen when tumor necrosis factor a was used as an ac tivator. Although potentiation was evident when MCG were added 6 h bef ore or after LPS stimulation, the maximum effect was noted when MCG an d LPS were added simultaneously, MCG-mediated enhancement of IL-6 prod uction was abrogated by pretreating MCG with protease inhibitors. Alth ough MCG proteases potentiate IL-6 production by HUVEC, they do not de grade secreted IL-6, These results demonstrate that MCG interact with endothelial cells and modulate the production of an important inflamma tory cytokine.