Hirono Ochi

Epicutaneous Allergic Sensitization by Cooperation between Allergen Protease Activity and Mechanical Skin Barrier Damage in Mice

Allergen sources such as mites, insects, fungi, and pollen contain proteases. Airway exposure to proteases induces allergic airway inflammation and IgE/IgG1 responses via IL-33-dependent mechanisms in mice. We examined the epicutaneous sensitization of mice to a model protease allergen, papain; the effects of tape stripping, which induces epidermal barrier dysfunction; and the atopic march upon a subsequent airway challenge. Papain painting on ear skin and tape stripping cooperatively promoted dermatitis, the skin gene expression of proinflammatory cytokines and growth factors, up-regulation of serum total IgE, and papain-specific IgE/IgG1 induction. Epicutaneous sensitization induced T helper (Th) 2 cells and Th17 differentiation in draining lymph nodes. Ovalbumin and protease inhibitor-treated papain induced no or weak responses, whereas the co-administration of ovalbumin and papain promoted ovalbumin-specific IgE/IgG1 induction. Wild-type and IL-33-deficient mice showed similar responses in the epicutaneous sensitization phase. The subsequent airway papain challenge induced airway eosinophilia and maintained high papain-specific IgE levels in an IL-33-dependent manner. These results suggest that allergen source-derived protease activity and mechanical barrier damage such as that caused by scratching cooperatively promote epicutaneous sensitization and skin inflammation and that IL-33 is dispensable for epicutaneous sensitization but is crucial in the atopic march upon a subsequent airway low-dose encounter with protease allergens.

Subcutaneous Allergic Sensitization to Protease Allergen Is Dependent on Mast Cells but Not IL-33: Distinct Mechanisms between Subcutaneous and Intranasal Routes

Protease activity of papain, a plant-derived occupational allergen homologous to mite major allergens, is essential to IgE/IgG1 production and lung eosinophilia induced by intranasal papain administration in mice, and IL-33 contributes to these responses. In this work, we investigate skin and Ab responses induced by s.c. papain administration into ear lobes and responses induced by subsequent airway challenge with papain. Subcutaneous papain injection induced swelling associated with increased epidermal thickness, dermal inflammation, serum IgE/IgG1 responses, and Th2 cytokine production in draining lymph node cells restimulated in vitro. These responses were markedly less upon s.c. administration of protease inhibitor-treated papain. Results obtained by using mast cell–deficient mice and reconstitution of tissue mast cells suggested the contribution of mast cells to papain-specific IgE/IgG1 responses and eosinophil infiltration. The responses were equivalent between wild-type and IL-33−/− mice. After the subsequent airway challenge, the s.c. presensitized wild-type mice showed more severe lung eosinophilia than those without the presensitization. The presensitized IL-33−/− mice showed modest lung eosinophilia, which was absent without the presensitization, but its severity and IgE boost by the airway challenge were markedly less than the presensitized wild-type mice, in which protease activity of inhaled papain contributed to the responses. The results suggest that mechanisms for the protease-dependent sensitization differ between skin and airway and that cooperation of mast cell–dependent, IL-33–independent initial sensitization via skin and protease-induced, IL-33–mediated mechanism in re-exposure via airway to protease allergens maximizes the magnitude of the transition from skin inflammation to asthma in natural history of progression of allergic diseases.

Airway inflammation after epicutaneous sensitization of mice requires protease activity of low-dose allergen inhalation

To the Editor: Epicutaneous exposure to allergens through the skin is considered to be an important route of sensitization. Allergen sources, such as mites, insects, fungi, and pollen, contain proteases, which are frequently allergens themselves. Recent studies using murine models of sensitization via skin or airways revealed that the protease activity of a model protease allergen, papain, is essential to the induction of inflammation at the sensitization sites and serum IgE/IgG1 responses. However, the role of allergen protease activity in effector-phase responses against lowdose antigen encounters after epicutaneous sensitization currently remains unknown. We herein examine the dependency of the onset of airway inflammation on the protease activity of antigens inhaled after epicutaneous presensitization in mice. We compared the dose dependency of responses to the intranasal administration of papain between epicutaneously presensitized (Fig 1, A-C) and naive mice (Fig 1,D-F) (for further information, see this article’s Online Repository at www. jacionline.org). The epicutaneous sensitization to papain induced elevations in total IgE and papain-specific IgE/IgG1 levels (Fig 1, C, Before; see Fig E1, A, in this article’s Online Repository at