Modulation Of Mast Cell Proteinase Activated Receptor Expression And IL-4 Release By IL-12

It has been recognized that proteinase activated receptors (PARs), interleukin (IL)-4 and IL-6 are involved in the pathogenesis of allergic diseases, and that IL-12 plays a role in adaptive immune response. However, little is knownof the effect of IL-12 on proteinase induced cytokine release from mast cells, and also the role of cytokine in modulating mast cell PAR expression and the actionof Th1 cytokine, IL-12, on mast cells, particularly on Th2 cytokine release frommast cells remain unclear. Therefore, we examined potential influence of IL-12on mast cell PAR expression and IL-4, IL-6 and histamine release as well as thepotential signal transduction pathways of IL-12 induced IL-4 release from mastcell P815.After being challenged, some of P815 cells were treated and analyzed byflowcytometry to detect expression of PPAs at protein level, some of cells weretreated and analyzed by real time RT-PCR to detect expression of PRAs at mRNA level, and other cells were treated and analyzed by cellular activation of signaling ELISA(CASE) to detect phosphorylation of ERK, Akt, p38 and STAT3, and the supernatantwere analysed by ELISA to detect the release of IL-4, IL-6 and histamine.The results showed that P815 cells expressed all four PARs both at proteinlevel and at mRNA level. IL-12 downregulated mast cell PAR-2 expression andupregulated PAR-4 expression both at protein level and at mRNA level as well asupregulated PAR-1 and PAR-3 mRNA expression. When P815 cells were primed with 1ng/ml of IL-12 for 60 minutes, trypsin and tryptase induced PAR-2 expression wereenhanced significantly both at protein level and at mRNA level, and this modulatoryaction of IL-12 were blocked by administration of IL-12 blocking antibody. IL-12 induced concentration dependent release of IL-4 from P815 cells following 16 hincubation. However, after the cells were primed with 1 ng/ml of IL-12 for 60 min, trypsin and tryptase induced IL-4 secretion were significantly reducedrespectively. FSLLRY-NH₂, an antagonist peptide of PAR-2 diminished trypsin andtryptase elicited IL-4 release, but did not affect IL-12 induced IL-4 release.PD98059, U0126 and LY294002 not only abolished IL-12 induced IL-4 release, butalso inhibited IL-12 induced phosphorylation of ERK and Akt.In conclusion, IL-12 can modulate mast cell PAR expression and IL-4 release.The IL-12 induced IL-4 release from P815 cells is most likely through activationof Akt and ERK signaling pathways, whereas tryptase and trypsin induced IL-4release appeared to depend on activation of mast cell PAR-2. These findingsimplicate that IL-12 may serve as a regulator in keeping the balance of Th1 andTh2 cytokine production in allergic inflammation through its ability in alteratingPAR-2 expression on mast cells and induction of IL-4 release from mast cells.Induction of IL-4 release from mast cells by tryptase may suggest a novelself-amplification mechanism of mast cell activation.