The present study was undertaken to evaluate the efficacy of GC oil alleviating atopic dermatitis-like immune alterations in mice. Even though GC oil has been historically used for the treatment of pruritic skin disorder [2
], there has been no scientific study investigating GC oil on the treatment or prevention of atopic dermatitis. Our study is the first to demonstrate GC oil's immunoregulatory potential for alleviating atopic dermatitis through influencing of Th2 cell activation. Overall, we found that GC oil possessed an ability to influence Th2 cell activation involved with the onset or progression of atopic dermatitis, in that dermal application of GC oil resulted in the suppression of IgE or IgG1 over-production, downregulation of IL-4 production from Th2 cells, and demonstrated a reduction in histamine release. In addition, frequent scratching due to itchy sensations was alleviated following GC oil application onto the damaged skin involved with the pathogenesis of atopic dermatitis.
Histamine release from activated mast cells or basophils is a hallmark of the occurrence of allergic diseases such as atopic dermatitis, and cause itching, increased vascular permeability, and the wheal and flare response of immediate hypersensitivity [1
]. Pruritus is a symptom found in a variety of skin disorders like atopic dermatitis and contact allergic dermatitis. For atopic dermatitis cases, it has been reported that scratching due to itchy sensations causes skin damage, promotes inflammation and thereby further aggravates pruritus [1
]. Therefore, it is important to reduce itchy sensations and scratching frequency to prevent aggravation of skin lesions due to pruritic disorders and improving quality of life.
Kobayashi et al. [19
] reported that the oral administration of GC extract combined with histamine receptor antagonists was more effective for the suppression of scratching behavior in mice than administration of histamine receptor antagonists alone. GC oil may inhibit the binding of histamine to its receptor, which will eventually control histamine mediated clinico-pathologic effects such as itching [20
]. Concerning our results showing the downregulation of serum histamine levels 2 weeks after the start of GC oil application following atopic dermatitis induction, this compound may also exhibit its anti-histamine effect by directly suppressing histamine release from mast cells through downregulation of IL-4 production from Th2 cells and following by suppression of IgE or IgG1 over-production.
The most important aspect to be discussed is GC oil's systemic effect on the modulation of the in vivo
type-2 response. The type-2 response becomes predominant when differentiation or activation of Th2 cells is preferred, but development or stimulation of Th1 cells is suppressed [13
]. Considering that the skewedness toward type-2 responses is a background mechanism for the occurrence of atopic dermatitis [1
], dermal application of GC oil could systematically block the pathogenesis of atopic dermatitis through correcting the immune homeostasis skewed in favor of Th2. Considering our experimental results, it could be concluded that the application of GC oil on the skin of atopic dermatitis cases could alter production of IL-4 from Th2 cells and also alter IgE, IgG1 and histamine production, performing a series of immunoregulatory functions to alleviate the occurrence or progression of atopic dermatitis. Hence, it is believed that the application of GC oil on atopic dermatitis cases will be significantly meaningful for public health and alternative medicine.
Although it is known that α-bisabolol has the strongest anti-inflammatory effects of all the constituents of GC oil, it is not clear which constituent(s) of GC oil contribute to the GC oil-mediated alleviation of atopic dermatitis-like immunologic and skin alterations in mice at the moment. Future studies will be directed towards identifying which components of GC oil are responsible for its immunomodulatory effects. Furthermore, whether GC oil exerts its immunomodulatory effects independently, sequentially, or concomitantly on each of the immune component cells involved in the pathogenesis of atopic dermatitis such as Th, B, and mast cells needs to be answered. Further investigations are necessary to identify target immune cells for GC oil-mediated alleviation of atopic dermatitis-like immunologic and skin alterations.