Elucidation of cytokines producing mechanism from basophils by the house dust mite major allergen, Der f 1

Abstract

House dust mite (HDMs) is one of the prevalent producers of allergens which can trigger inflammatory diseases such as allergic asthma, rhinitis and atopic dermatitis.1,2 More than thirty house dust mite proteins have been described from two predominant dust mite species, Dermatophagoides pteronyssinus and Dermatophagoides farinae. Group 1 major allergens (Der p 1, Der f 1), a papain-like cysteine protease, are the potent inducers of allergic inflammation by disruption of tight junction proteins and increasing the permeability of epithelial cells 3,4 In addition, they can destroy an inhibitory feedback mechanism that normally limits IgE synthesis by cleaving CD23 in B cells and increase production of Th2 cytokines by cleaving CD25 in T cells.5,6 It also able to cleave N-terminal ‘tethered ligand’ of proteinase-activated receptors (PARs) subsequently activating the immune cells expressing PARs.7 A recent study has proved that a naive T cells respond to the allergen containing protease activity through a PAR-2 and can produce various cytokines and chemokines. It implies that PARs are activated by proteolytic cleavage, which might be mediated by cysteine protease.8 Thus, these enzymatic functions of the mite group 1 allergens may play a role in immune responses.Basophils are the least common granulocytes in the peripheral blood and account for less than 1% of all leukocytes. Basophils have morphological and functional resemblance to tissue-resident mast cells: both cells express FcεRI and produce histamine, leukotriene and cytokines9, which imply their involvement in immune responses. Despite of sharing these phenotypic characteristics, basophils and mast cells have apparent differences.10 Basophils are circulating granulocytes that mature in the bone marrow and barely present in tissues.11 In addition, they may be recruited to inflammatory sites where induce

immediate hypersensitivity reaction and IgG1-mediated systemic anaphylactic shock.12 Many studies also clarified that basophils play critical roles in Th2 immune response to generate a large amount Th2 cytokines such as IL-4 and IL-13 in both humans and mice.13 Thus, basophils-derived inflammatory mediators play important role in the development of acute and chronic allergic responses. A recent study has suggested that basophils able to infiltrate rapidly into the inflamed skin and subsequently attract eosinophils for the development of inflammation lesions using murine models.14 Sokol et al. have reported that cysteine protease allergens directly target basophils in the absence of IgE-allergen complex, such as the production of Th2-promoting cytokines and induction of Th2 cell differentiation in vivo.15 Another study suggested that basophils are thought to induce the expression of cytokines by proteolytic activities of proteins, contributing to the development of a cytokine milieu.16 However, the mechanisms by which of protease allergens mediate basophil activation remain undefined.This study wanted to see whether the basophils are activated by the stimulation of protease allergen, Der f 1, in IgE-independent way.First chapter shows that rDer f 1 can act directly to activate human basophilic cell line KU812 and increase inflammatory chemokine IL-8 levels independent on IgE-mediated mechanism. rDer f 1 increased the DNA binding activity of activator protein-1 (AP-1), which suggested that the AP-1 binding might be involved in rDer f 1-induced IL-8 production. Furthermore, results implied that rDer f 1 induced IL-8 expression was sensitive to pharmacological inhibition of ERK and p38 mitogen-activated protein kinase (MAPK) signaling pathways and partially associated with the generation of reactive oxygen species (ROS). Second chapter suggests how cysteine protease

allergen rDer f 1 triggers Th2 cytokine such as IL-4 and IL-13 from mouse bone marrow derived basophils (BMBs). BMBs derived-Th2 cytokines could be induced by active rDer f 1, independent on IgE and TLR 2 and 4. BMBs express protease activated receptors (PAR-1, -3 and -4), and their expression was shown to be affected by enzymatic activity of allergen. However, but not PAR, G protein coupled receptors were found to be associated with production of IL-4 and IL-13 from BMBs upon Der f 1 treatment. In addition, the secretion of Th2 cytokines from basophils activated by Der f 1 was mediated by G protein βγ, PI3K and ERK, JNK MAPK pathways.