title: Mast cell alpha-chymase reduces IgE recognition of birch pollen profilin by cleaving antibody-binding epitopes.
abstract: In sensitized individuals birch pollen induces an allergic response characterized by IgE-dependent mast cell degranulation of mediators, such as alpha-chymase and other serine proteases. In birch and other plant pollens, a major allergen is profilin. In mammals, profilin homologues are found in an intracellular form bound to cytoskeletal or cytosolic proteins or in a secreted form that may initiate signal transduction. IgE specific to birch profilin also binds human profilin I. This cross-reactivity between airborne and endogenous proteins may help to sustain allergy symptoms. The current work demonstrates that cultured mast cells constitutively secrete profilin I, which is susceptible to degranulation-dependent proteolysis. Coincubation of chymase-rich BR mastocytoma cells with Ala-Ala-Pro-Phe-chloromethylketone (a chymase inhibitor) blocks profilin cleavage, which does not occur in degranulated HMC-1 mast cells, which are rich in tryptase, but chymase deficient. These data implicate chymase as the serine protease cleaving secreted mast cell profilin. Sequencing of chymase-cleaved profilins reveals hydrolysis at Tyr(6)-Val(7) and Trp(35)-Ala(36) in birch profilin and at Trp(32)-Ala(33) in human profilin, with all sites lying within IgE-reactive epitopes. IgE immunoblotting studies with sera from birch pollen-allergic individuals demonstrate that cleavage by chymase attenuates binding of birch profilin to IgE. Thus, destruction of IgE-binding epitopes by exocytosed chymase may limit further mast cell activation by this class of common plant allergens, thereby limiting the allergic responses in sensitized individuals.
authors.affiliation: Cardiovascular Research Institute, University of California, San Francisco, CA 94143, USA.
authors.forename: Matthew B
authors.initials: MB
authors.lastname: Mellon
authors.forename: Brendon T
authors.initials: BT
authors.lastname: Frank
authors.forename: Kenneth C
authors.initials: KC
authors.lastname: Fang
mesh_terms: D000485:Allergens / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D029662:Betula / Q000276:immunology*; D001666:Binding Sites, Antibody; D015550:Cell Degranulation; D002460:Cell Line; D053818:Chymases; D003285:Contractile Proteins; D004285:Dogs; D000939:Epitopes / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D007073:Immunoglobulin E / Q000276:immunology*; D008407:Mast Cells / Q000201:enzymology / Q000276:immunology*; D008840:Microfilament Proteins / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011058:Pollen / Q000276:immunology*; D051304:Profilins; D012697:Serine Endopeptidases / Q000378:metabolism / Q000502:physiology*; D014407:Tumor Cells, Cultured
chemical_list: D000485:Allergens; D003285:Contractile Proteins; D000939:Epitopes; D008840:Microfilament Proteins; D051304:Profilins; D007073:Immunoglobulin E; D012697:Serine Endopeptidases; D053818:Chymases