Atopic dermatitis is a biphasic inflammatory skin disease, provoked by an imbalance between Th1 and Th2 immune responses [4
]. Th2 immune responses are mediated by interleukin (IL)-4, IL-5, and IL-13 while Th1 immune responses are modulated by IFN-γ
]. In particular, Th2 responses are key elements to the pathogenesis of atopic disorders. NC/Nga mice were the first mouse model of AD reported by Matsuda et al. [21
], and the mice treated with DFBN, DNCB, or picryl chloride have also been used as an animal model for human AD [22
]. Elevated levels of serum total IgE have been reported to correlate with the appearance of the AD-like lesions in NC/Nga mice, with massive infiltration of IL-4- and IL-13-producing Th2 cells and the degranulation of mast cells and eosinophils [4
]. HC is a potent topical corticosteroid used to alleviate rash, eczema, and dermatitis. However, HC is a steroidal agent with adverse effects such as facial hypertrichosis, folliculitis, miliaria, and genital ulcers [23
], which has inspired to investigations of nonsteroidal agents for relieving AD. Recently, several studies have reported that Herbal Oriental Medicine therapy may be effective in AD patients [24
]. The present study showed that CIL dose dependently reduced the severity of AD-like skin lesions by decreasing serum IgE and IgG1 levels and infiltration of mast cells and eosinophils in DNCB-treated NC/Nga mice. The results also indicate that the effects of CIL were probably due to a decrease in IFN-γ
, IL-4, and IL-13 production by activated Th1 and Th2 cells. CIL-High was found to be as effective as HC for alleviating AD.
Mast cells are known as key effector cells in IgE-mediated allergic disorders and are activated by cross-linking of a high affinity IgE receptor [3
]. Upon activation, mast cells undergo degranulation and release a variety of biologically active substances, which play an important role in host defense and allergic reactions including AD. Infiltration of mast cells into the dermis is a necessary characteristic for defining an appropriate animal model for AD [25
]. We investigated the efficacy of CIL for preventing AD-like skin lesions in DNCB challenged NC/Nga mice and its mechanism for preventing and alleviating AD was explored since CIL has been widely used as an anti-inflammatory agent in Southeast Asian folk medicine. We found that CIL-High significantly suppressed the numbers of mast cells infiltrating in the skin lesions of the atopic dermatitis mice, suggesting that the activation and migration of mast cells may be an immunopharmacological target of CIL-High.
It is known that mast cell activation is tightly modulated by IgE from B cells, and increased total serum IgE levels are a hallmark of AD [24
]. AD induced by DNFB application activates B cells in NC/Nga mice by a Th2 reaction through IL-4 that elevates IgE production [25
]. IgE expression is known to cause both acute and chronic phase skin symptoms. Consistent with these reports, we found that serum IgE levels were significantly increased by repeated DNCB application in NC/Nga mice, as was IL-4 and IL-13 production by activated Th2 cells. These cytokines are known to play important roles in the inflammation and hypertrophy of the skin in AD [25
]. We also found that higher IgE, IL-4, and IL-13 levels were associated with more severe skin lesions. Topical application of CIL-High significantly improved the severity of AD-like skin lesions by suppressing serum IgE, IL-4, and IL-13 levels. The improvement by CIL-High was as effective as with HC.
In addition to cytokines released from Th2 cells, Th1 cytokines such as INF-γ
are involved in AD development [4
]. Under normal conditions, the differentiation of naive T cells to Th1 and Th2 lineages is regulated by cytokines that are secreted from various cells, including themselves, and the Th1/Th2 balance is maintained [6
]. However, in atopic dermatitis, the balance shifts to Th2 dominance; this eventually leads to excessive Th2 cytokine production [6
]. Some studies have found that increased INF-γ
levels alleviate AD-like symptoms, but those results remain controversial. In the present study, repeated DNCB application increased both IFN-γ
and IL-4 production from activated CD4+
T cells of draining lymph nodes in NC/Nga mice. CIL dose dependently decreased both Th1 (INF-γ
) and Th2 cytokines (IL-4 and IL-13) as effectively as HC. Furthermore, the ratio of Th1 to Th2 cytokines was increased by CIL treatment.
In conclusion, CIL-High reduced the development of AD-like skin lesions resulting from repeated DNCB application in NC/Nga mice by suppressing total serum IgE levels and IFN-γ and IL-4 production by activated CD4+ T cells. CIL-High ameliorated AD symptoms as effectively as HC. Sesquiterpenes and flavonoids in CIL may be the active components exerting anti-AD-like effects; further study is needed to identify the primary active components.