The bark of Betula platyphylla var. japonica inhibits the development of atopic dermatitis-like skin lesions in NC/Nga mice

The bark of Betula platyphylla Sukat. var. japonica Hara (Asian White Birch, AWB) is one of the herbs used in Eastern countries for the treatment of various inflammatory diseases including atopic dermatitis (AD). The present study was performed to examine if and how the bark of AWB inhibits the development of AD-like skin lesions in NC/Nga mice induced by repeated application of picryl chloride (PC). With this aim, we examined the skin symptom severity, itching behavior, serum immunoglobulin (Ig) E level and mRNA expression of cytokines at iliac and cervical lymph nodes in the mice. Oral administration of AWB extracts (25, 100 and 250 mg/kg) to the PC-treated mice inhibited the development of AD-like skin lesions as exemplified by a significant decrease in the total skin severity scores, itching behavior and a decrease in hypertrophy and infiltration of inflammatory cells into dermis. The serum IgE level was also significantly reduced by AWB extract. In the RT-PCR results, the expression of interleukin-4 mRNA was reduced by AWB extract, whereas the expression of interferon-γ mRNA was not changed. These results suggest that AWB inhibits the development of AD-like skin lesions in NC/Nga mice through the suppression of the T-helper 2 cell response.