Mast cells are required for full expression of allergen/SEB-induced skin inflammation

Abstract

Atopic dermatitis (AD) is a chronic pruritic inflammatory skin disease. We recently described an animal model in which repeated epicutaneous applications of a house dust mite extract and Staphylococcal enterotoxin B induced eczematous skin lesions. In this study we showed that global gene expression patterns are very similar between human AD skin and allergen/staphylococcal enterotoxin B-induced mouse skin lesions, particularly in the expression of genes related to epidermal growth/differentiation, skin barrier, lipid/energy metabolism, immune response, or extracellular matrix. In this model, mast cells and T cells, but not B cells or eosinophils, were shown to be required for the full expression of dermatitis, as revealed by reduced skin inflammation and reduced serum IgE levels in mice lacking mast cells or T cells (TCRβ(-/-) or Rag1(-/-)). The clinical severity of dermatitis correlated with the numbers of mast cells, but not eosinophils. Consistent with the idea that T helper type 2 (Th2) cells play a predominant role in allergic diseases, the receptor for the Th2-promoting cytokine thymic stromal lymphopoietin and the high-affinity IgE receptor, FcɛRI, were required to attain maximal clinical scores. Therefore, this clinically relevant model provides mechanistic insights into the pathogenic mechanism of human AD.

Figure 1. T cells, but not B cells, are indispensable for maximal skin inflammation

Dermatitis induction by epicutaneous applications of Der f and SEB was performed as described in the Materials and Methods. Each symbol represents one mouse. (A) Clinical skin scores. (B) H&E staining of naïve (upper rows) and lesional (lower rows) skin tissues. Bar, 200 µm. (C) Thicknesses of epidermis, dermis, and total skin (epidermis + dermis) layers, as measured in H&E-stained tissues. (D) Relationships between clinical scores and skin layer thicknesses. Linear regression lines are shown. *, p<0.05; **, p<0.01; ***, p<0.001; ****, p<0.0001; n.s., not significant.

Figure 2. Eosinophils are dispensable for allergen-induced skin inflammation

(A,B) Eosinophils stained with Congo red were enumerated in the skin sections derived from experiments shown in Fig. 1. Each symbol represents one mouse. There was no significant correlation between eosinophil numbers and clinical scores. (C,D) Dermatitis induction by epicutaneous applications of Der f and SEB was performed on eosinophil-deficient PHIL (C) and ΔdblGATA (D) mice. Clinical scores are shown.

Figure 3. Mast cells are indispensable for maximal skin inflammation

(A) Mast cell-deficient Kit^W-sh/W-sh mice exhibited lower clinical scores than WT mice. The scores similar to WT mice were restored by engraftment of BMMC (W-sh + BMMC). (B) H&E staining of naïve and lesional skin tissues. Enlarged images of the areas indicated by rectangles are shown below. Bar, 200 µm. (C) Thicknesses of epidermis, dermis, and total skin layers. (D) Immunofluorescence microscopy was performed on naïve and lesional skin tissues. Numbers of eosinophil (E) and neutrophil (F) before and after AD induction. *, p<0.05; **, p<0.01; ***, p<0.001; n.s., not significant.

Figure 4. FcεRI, but not TNF-α, is required for maximal skin inflammation

Der f/SEB induction experiments were performed on FcεRIα^−/− (A–E) and TNF-α^−/− (F) mice. (A, F) Clinical skin scores. Thicknesses of epidermis, dermis, and total skin layers (B, C, D), and inflammatory cell infiltration (E) for these mice are also shown. (B) H&E staining and (D) immunofluorescence microscopy were performed on naïve and lesional skin tissues in FcεRIα^−/− mice. *, p<0.05; n.s., not significant.

Figure 5. The Th2-promoting cytokine TSLP contributes to skin inflammation

(A) Expression of TSLP (red) before (Upper) and after (Lower) dermatitis induction with Der f/SEB in WT mice was revealed by immunofluorescence microscopy. Also shown are enlarged images of the areas indicated by rectangles as well as negative control without primary antibody. Bar, 100 µm. (B–F) Der f/SEB induction experiments were performed on TSLPR^−/− mice. (B) Clinical skin scores, (C,D) thicknesses of epidermis, dermis, and total skin layers, and (E) inflammatory cell infiltration are shown. (C) H&E staining and (F) immunofluorescence microscopy were performed on naïve and lesional skin tissues in TSLPR^−/− mice. **, p<0.01; ***, p<0.001 by Student’s t -test.