Atopic dermatitis (AD) usually develops in patients with an individual or family history of allergic diseases, and is characterized by chronic relapsing inflammation seen especially in childhood, association with IgE hyperproduction and precipitation by environmental factors. However, the exact etiology of AD has been unclear. To further explore the pathogenesis and treatment of AD, a suitable animal model is required. We found that skin lesions, which were clinically and histologically very similar to human AD, spontaneously appeared on the face, neck, ears and dorsal skin of inbred NC/Nga mice when they were raised in non-sterile (conventional) circumstances, but not under specific pathogen-free conditions. Plasma levels of total IgE in conventional NC/Nga mice were markedly elevated from 8 weeks of age, correlating with clinical skin severity of dermatitis. Immunohistochemical examination of the skin lesion showed increased numbers of mast cells and CD4+ T cells containing IL-4 necessary for IgE synthesis. Thus, NC/Nga mice suffered from dermatitis very similar to human AD with IgE hyperproduction, which may be triggered by some environmental factor(s).

Summary: The mast cell is one of the major effector cells in inflammatory reactions and can be found in most tissues throughout the body. During inflammation, an increase in the number of mast cells in the local milieu occurs, and such accumulation requires directed migration of this cell population. As it has previously been reported that the human cathelicidin‐derived antibacterial peptide, LL‐37, stimulates the degranulation of mast cells, we hypothesized that LL‐37 could be a mast cell chemotaxin. The present study shows that LL‐37 is a potent chemotactic factor for mast cells. The chemotactic response was dose‐dependent and bell‐shaped, reaching an optimal concentration of 5 µg/ml. In addition, checkerboard analysis showed that cell migration towards this peptide was chemotactic rather than chemokinetic. Moreover, Scatchard analysis using ¹²⁵I‐labelled LL‐37‐derived peptide revealed that LL‐37 has at least two classes of receptors, namely high‐ and low‐affinity receptors, on mast cells. Furthermore, the competitive binding assay suggested that LL‐37 is unlikely to utilize formyl peptide receptor‐like 1 (FPRL1), a functional LL‐37 receptor for neutrophil and monocyte migration, on mast cells. In addition, the treatment of cells with pertussis toxin and phospholipase C inhibitor, U‐73122, inhibited LL‐37‐mediated migration, indicating that LL‐37 induces mast cell chemotaxis through a Gi protein‐phospholipase C signalling pathway. These results show that besides its antibacterial activities, LL‐37 may have the potential to recruit mast cells to inflammation foci.

Atopic dermatitis (AD) is a common pruritic disease that occurs primarily in infancy and childhood. AD is characterized by itching and the patient having an individual or family history of atopic diseases. Although AD is also frequently associated with elevated serum IgE levels and with common environmental factors contributing to its pathogenesis, the etiology of AD is still unknown. We examined NC/Nga mice (NC mice) that showed AD-like skin lesions with aging as a possible mouse model for AD. NC mice were maintained under conventional (Conv) or specific pathogen-free (SPF) conditions. Clinical symptoms, serum IgE levels and histopathology of the skin were compared between these 2 groups, and we explored their application as a model of human AD. It was found that the skin lesions of inbred NC mice were clinically and histologically very similar to human AD when the mice were raised under Conv conditions, but not under SPF conditions, and we assumed that some kinds of environmental factors might trigger AD-like signs and symptoms in NC mice. To further investigate the pathophysiology and treatment of AD, a suitable animal model is absolutely required, and NC mice are very useful for this purpose.

The effect of nerve growth factor (NGF) on proliferation/differentiation of mast cells was investigated in vitro. Although NGF alone neither supported colony formation of bone marrow-derived cultured mast cells (BMCMC) nor induced development of mast cell colonies from nonadherent bone marrow cells (NBMC), addition of NGF to the suboptimal dose of interleukin 3 (IL-3) significantly increased the numbers of mast cell colonies produced by BMCMC or NBMC in methylcellulose. When stimulated by IL-3 alone, cells in mast cell colonies were not stained by berberine sulfate, a fluorescent dye. In contrast, mast cells developing in methylcellulose cultures obtaining both IL-3 and NGF were stained by berberine sulfate. The fluorescence was abolished by the treatment of heparinase but not of chondroitinase ABC, suggesting that mast cells stimulated by IL-3 and NGF produced and stored heparin proteoglycan. The histamine content of BMCMC maintained by IL-3 was also increased by addition of NGF. Since BMCMC showed mucosal mast cell-like phenotype, NGF appeared to induce the phenotypic change to connective tissue-type mast cells (CTMC). In the culture containing BMCMC, 3T3 fibroblasts, and IL-3, the phenotypic change of BMCMC to CTMC was observed as well. Since NGF was detected in this coculture and since addition of anti-NGF monoclonal antibody suppressed the phenotypic change, NGF produced by fibroblasts appeared to induce the phenotypic change. Neither BMCMC alone nor IL-3 alone increased the concentration of NGF. Therefore, there is a possibility that BMCMC stimulated by IL-3 may induce the production and/or release of NGF by fibroblasts.

Mast cells are known to accumulate at the sites of inflammation in response to chemoattractants generated in the local milieu. Since human β‐defensin‐2 (hBD‐2) is generated in several epithelial tissues where mast cells are present and because we have recently reported that this human antibacterial peptide induces mast cell degranulation, we thus hypothesized that hBD‐2 could be a mast cell chemotaxin. Here we report that hBD‐2 directly and specifically induces mast cell migration with an optimal concentration of 3 µg/ml. Checkerboard analysis showed that the migration was more chemotactic rather than chemokinetic. Moreover, Scatchard analysis using ¹²⁵I‐labeled hBD‐2 revealed that mast cells have at least two classes of receptors, high‐ and low‐affinity receptors, for this peptide. Moreover, the competitive binding assay suggested that hBD‐2 is unlikely to utilize CCR6, a functional receptor for hBD‐2‐mediated dendritic and T cell migration, on mast cells. In addition, treatment of mast cells with G protein inhibitor, pertussis toxin, and phospholipase C inhibitor, U‐73122, abolished the cell chemotaxis in response to hBD‐2, indicating that the G protein–phospholipase C signaling pathway is involved in hBD‐2‐induced mast cell activation. Thus, we suggest that hBD‐2, which was originally believed to be involved in innate host defense, may participate in the recruitment of mast cells to inflammation foci.

Four full-thickness skin wounds made in normal mice led to the significant increase in levels of nerve growth factor (NGF) in sera and in wounded skin tissues. Since sialoadenectomy before the wounds inhibited the rise in serum levels of NGF, the NGF may be released from the salivary gland into the blood stream after the wounds. In contrast, the fact that messenger RNA and protein of NGF were detected in newly formed epithelial cells at the edge of the wound and fibroblasts consistent with the granulation tissue produced in the wound space, suggests that NGF was also produced at the wounded skin site. Topical application of NGF into the wounds accelerated the rate of wound healing in normal mice and in healing-impaired diabetic KK/Ta mice. This clinical effect of NGF was evaluated by histological examination; the increases in the degree of reepithelialization, the thickness of the granulation tissue, and the density of extracellular matrix were observed. NGF also increased the breaking strength of healing linear wounds in normal and diabetic mice. These findings suggested that NGF immediately and constitutively released in response to cutaneous injury may contribute to wound healing through broader biological activities, and NGF improved the diabetic impaired response of wound healing.