Aggravation of atopic dermatitis-like symptoms by consecutive low concentration of formaldehyde exposure in NC/Nga mice.

Formaldehyde (FA) has been known to be associated with development of asthma (AS) and atopic dermatitis (AD). In this study, we investigated whether FA inhalation would affect the provocation or exacerbation of AD-like symptoms. Atopic-prone NC/Nga mice were exposed to low (0.2 ppm) and high (1.0 ppm) concentration of FA by inhalation. Combined exposure to low concentration of FA inhalation and topical house dust mite (HDM) stimulation significantly upregulated HDM-induced total plasma IgE and IgG2a production, Th1-, Th2-, Th17-related cytokine as well as COX-2 mRNA expressions in the skin. Interestingly, independent FA inhalation, especially at low concentration (0.2 ppm), increased the skin mRNA expressions of IL-13, IL-17E/IL-25 and COX-2, even though it failed to induce AD-like skin inflammation. In conclusion, we suggest that increased skin mRNA expressions of IL-13, IL-25/IL-17E and COX-2 by independent low concentration of FA exposure might be a key factor to exacerbate HDM-mediated AD-like skin inflammation.