Hirotaka Yamashita

Mast Cells Are Required for Full Expression of Allergen/SEB-Induced Skin Inflammation

Atopic dermatitis 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 atopic dermatitis skin and allergen/staphylococcal enterotoxin B-induced mouse skin lesions, particularly in 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 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, FcεRI, were required to attain maximal clinical scores. Therefore, this clinically relevant model provides mechanistic insights into the pathogenic mechanism of human atopic dermatitis.

Critical Role for Mast Cell Stat5 Activity in Skin Inflammation

SUMMARY Atopic dermatitis (AD) is a chronic inflammatory skin disease. Here, we show that phospholipase C-β3 (PLC-β3)-deficient mice spontaneously develop AD-like skin lesions and more severe allergen-induced dermatitis than wild-type mice. Mast cells were required for both AD models and remarkably increased in the skin of Plcb3−/− mice because of the increased Stat5 and reduced SHP-1 activities. Mast cell-specific deletion of Stat5 gene ameliorated allergen-induced dermatitis, whereas that of Shp1 gene encoding Stat5-inactivating SHP-1 exacerbated it. PLC-β3 regulates the expression of periostin in fibroblasts and TSLP in keratinocytes, two proteins critically involved in AD pathogenesis. Furthermore, polymorphisms in PLCB3, SHP1, STAT5A, and STAT5B genes were associated with human AD. Mast cell expression of PLC-β3 was inversely correlated with that of phospho-STAT5, and increased mast cells with high levels of phospho-STAT5 were found in lesional skin of some AD patients. Therefore, STAT5 regulatory mechanisms in mast cells are important for AD pathogenesis.

Dermal mast cells play a central role in the incidence of scratching behavior in mice induced by multiple application of the hapten, 2,4,6‐trinitrochlorobenzene

Abstract:  Repeated application of 1% 2,4,6‐trinitrochlorobenzene (TNCB) in acetone solution causes chronic skin inflammation in BALB/c mice. Associated scratching behavior gradually appeared, and chronic scratching behavior was established over 40 days after the initial application of TNCB. In order to explore the possible involvement of T cells and mast cells in the appearance of pruritus, we examined the response of athymic nude mice and genetically mast‐cell‐deficient mice. We could not detect either severe skin inflammation or immunoglobulin (Ig)E production in T‐cell‐deficient BALB/c nu/nu mice even after 80 days of TNCB treatment, whereas typical severe skin inflammation and IgE production were observed in mast‐cell‐deficient WBB6F1‐W/Wv and WBB6F1‐Sl/Sld mice. Furthermore, we observed persistent scratching behavior in WBB6F1‐W/Wv mice, but not in BALB/c nu/nu and WBB6F1‐Sl/Sld mice. Histological examination of TNCB‐treated animals revealed the development of dermal mast cells in W/Wv mice but not in Sl/Sld mice. Degranulation of dermal mast cells was observed in the WBB6F1‐W/Wv genotype, but most mast cells remained intact in TNCB‐treated BALB/c nu/nu mice. These results suggest that mast cells play a pivotal role in the incidence of scratching behavior in this chronic pruritus model.

The role of IgE and repeated challenge in the induction of persistent increases in scratching behavior in a mouse model of allergic dermatitis

Previously, we indicated that athymic BALB/c-nu/nu (nude) mice that had been repeatedly treated with 2,4,6-trinitrochlorobenzene (TNCB) failed to exhibit chronic scratching behavior in spite of the accumulation of dermal mast cells in the lesion. The mice also failed to produce specific IgE or potent dermatitis. In the present study, therefore, we aimed to examine the role of IgE and repeated hapten treatment in the induction of scratching behavior and dermatitis using nude mice and trinitrophenol (TNP)-specific IgE-transgenic mice. The ears of nude mice were treated with TNCB 6 times at intervals of 48 h, and TNP-specific IgE was administered to the mice intravenously before the sixth TNCB treatment. The nude mice that had been supplemented with IgE exhibited a persistent increase in scratching behavior and continuous degranulation of mast cells. Furthermore, a potent immediate ear swelling was induced, although no biphasic dermatitis pattern was observed. On the other hand, the IgE-transgenic mice failed to exhibit persistent increases in scratching behavior after a single TNCB treatment, although biphasic ear swelling was observed. These results indicate that specific IgE plays an essential role in the induction of persistent increases in scratching behavior and continuous degranulation of mast cells. Furthermore, repeated challenge with the hapten also plays an important role in persistent increases in scratching behavior through accumulation and continuous activation of mast cells.

Histamine-releasing factor enhances food allergy

Food allergy occurs due to IgE- and mast cell–dependent intestinal inflammation. Previously, we showed that histamine-releasing factor (HRF), a multifunctional protein secreted during allergy, interacts with a subset of IgE molecules and that the HRF dimer activates mast cells in an HRF-reactive IgE-dependent manner. In this study, we investigated whether HRF plays any role in food allergy. Specifically, we determined that prophylactic and therapeutic administration of HRF inhibitors that block HRF-IgE interactions reduces the incidence of diarrhea and mastocytosis in a murine model of food allergy. Food allergy–associated intestinal inflammation was accompanied by increased secretion of the HRF dimer into the intestine in response to proinflammatory, Th2, and epithelial-derived cytokines and HRF-reactive IgE levels at the elicitation phase. Consistent with these data, patients with egg allergy had higher blood levels of HRF-reactive IgE compared with individuals that were not hypersensitive. Successful oral immunotherapy in egg-allergy patients and food-allergic mice reduced HRF-reactive IgE levels, thereby suggesting a pathological role for HRF in food allergy. Together, these results suggest that antigen and HRF dimer amplify intestinal inflammation by synergistically activating mast cells and indicate that HRF has potential as a therapeutic target in food allergy.

Eppikajutsuto Protects against Food Allergy Induced by Ovalbumin in a Murine Model

Background: Currently, there are no efficient medications available for the prevention and treatment of food allergy (FA). Herbal medicines, including traditional Japanese Kampo medicines (TJKMs), are promising therapeutic drugs. Methods: We screened 18 TJKMs for treatment of FA symptoms in a mouse FA model induced by ovalbumin (OVA). BALB/c mice were sensitized intraperitoneally by an OVA/aluminum hydroxide gel mixture followed by 4 booster doses of oral OVA and FA symptom induction by 50 mg of OVA. TJKMs were orally administered for 28 days from the day of sensitization to the day before FA symptom induction. Evaluated FA symptoms included a decrease in body temperature and allergic diarrhea. Allergic sensitization was determined by plasma OVA-specific IgE levels. Cytokine mRNA levels in mesenteric lymph nodes, plasma mouse mast cell protease-1, and the number of mast cells in the small and large intestines were analyzed. Additionally, the therapeutic effect of the TJKM eppikajutsuto (EJT) on mast cell degranulation was determined in active anaphylaxis and passive cutaneous anaphylaxis models. Results: EJT effectively prevented FA symptoms. Although OVA-specific IgE levels and the intestinal mast cell numbers were not different between the EJT-treated and untreated FA mice, plasma mMcpt1 and IL-4 levels were lower in EJT-treated FA mice than untreated FA mice. EJT could alleviate symptoms in both active and passive anaphylaxis models. Conclusion: EJT prevented OVA-induced FA symptoms in a mouse model, suggesting that EJT might exert its therapeutic activity via IL-4 suppression and the inhibition of mucosal mast cell degranulation.

Immunomodulatory effects of lovastatin on ovalbumin-induced bronchial asthma in mice

Objectives: Lovastatin (LOV) is a cholesterol-lowering agent with immunomodulatory and anti-inflammatory effects. The present study evaluated the immunomodulatory effects of LOV in a mouse model of bronchial asthma. Methods: Mice were sensitized by giving 50 μg ovalbumin (OVA) i.p. with 1 mg alum on days 0 and 12. From day 22, mice were exposed to OVA (1% (w/v) in saline for 30 min, three times every 4th day. Negative control received saline similarly. Oral LOV, given 31 days, was starting from day 0 to day 30 and at sensitization day; it was given 30 min before the treatment. The number of inflammatory cells, levels of interleukin (IL)-4, IL-5, IL-13 and interferon (IFN)- in bronchoalveolar lavage fluid (BALF), serum IgE, OVA-specific IgE, IgG1 and IgG2a levels, in addition to histopathological and immunohistochemical examination of the lung were investigated. Results: LOV showed significant decrease in the number of leukocytes, macrophages and eosinophils, levels of IL-4, IL-5 and IL-13 in BALF, serum levels of IgE, OVA-specific IgE and IgG1, but no significant effect on BALF level of IFN- and serum level of OVA-specific IgG2a, in addition to the improvement of the histopathological and immunohistochemical changes. Conclusion: These results suggest that LOV could be beneficial for the treatment of bronchial asthma.