Allergen cleavage by effector cell-derived proteases regulates allergic inflammation.

The key event of allergic inflammation, allergen-induced crosslinking of mast cell-bound IgE antibodies, is accompanied by release of inflammatory mediators, cytokines, and proteases, in particular beta-tryptase. We provide evidence that protease-mediated cleavage of allergens represents a mechanism that regulates allergen-induced mast cell activation. When used in molar ratios as they occur in vivo, purified beta-tryptase cleaved major grass and birch pollen allergens, resulting in defined peptide fragments as mapped by mass spectrometry. Tryptase-cleaved allergens showed reduced IgE reactivity and allergenic activity. The biological relevance is demonstrated by the fact that lysates from activated human mast cells containing tryptase levels as they occur in vivo cleaved allergens. Additionally, protamine, an inhibitor of heparin-dependent effector cell proteases, augmented allergen-induced release of mediators from effector cells. Protease-mediated allergen cleavage may represent an important mechanism for terminating allergen-induced effector cell activation.

IFN-gamma-enhanced allergen penetration across respiratory epithelium augments allergic inflammation.

BACKGROUND: Respiratory allergen contact is the critical event in the elicitation and boosting of allergen-specific immune responses, as well as in the induction of immediate and late inflammatory reactions. OBJECTIVE: We sought to investigate the influence of various factors of allergic inflammation on the integrity and barrier function of respiratory epithelium for allergens. METHODS: We cultured the human bronchial epithelial cell line 16HBE14o- in a transwell culture system as a surrogate of intact respiratory epithelium and used purified iodine 125-labeled recombinant major birch pollen allergen (rBet v 1) to study the extent, kinetics, and factors influencing transepithelial allergen penetration. RESULTS: Culture supernatants from activated allergen-specific T H 1 clones decreased transepithelial resistance. A screening of various factors (histamine, IFN-gamma, IL-1beta, IL-2, IL-3, IL-4, IL-5, IL-8, IL-12, and TNF-alpha) identified IFN-gamma as a potent factor capable of reducing epithelial barrier properties and enhancing transepithelial allergen penetration. Increased submucosal allergen concentrations caused by IFN-gamma-mediated reduction of epithelial barrier function provoked a more than 7-fold augmentation of histamine release from sensitized basophils. CONCLUSION: These results demonstrate that the T H 1 cell-derived cytokine IFN-gamma facilitates allergen penetration through the respiratory epithelium and thereby can aggravate allergic inflammation.