Itch-associated scratching contributes to the development of dermatitis and hyperimmunoglobulinaemia E in NC/Nga mice

Atopic dermatitis (AD) is related to immunoglobulin E (IgE) production, and a type-1 and type-2 helper T cell (Th1/Th2) imbalance has been hypothesized as the aetiology. While itching and scratching are important factors in the development of dermatitis, the mechanisms underlying these phenomena are poorly understood. We investigated the relationship between scratching, transepidermal water loss (TEWL), signs of dermatitis and serum Ig levels in NC/Nga mice, a model of AD. We also sensitized specific pathogen-free (SPF)NC/Nga mice and BALB/c mice to mite antigen to determine the effects of IgE overproduction on scratching and investigated the involvement of mast cells and T/B cells in the induction of scratching using WBB6F1-W/W-v mice and C.B.17/Icr-scid mice. Under conventional conditions, the scratch counts increased, followed by increases in TEWL and the inflammation score in NC/Nga mice that were not kept under SPF conditions. However, no change was observed in scratching, TEWL, or signs of dermatitis in mite antigen-sensitized SPF-NC/Nga and BALB/c mice, although the serum total IgE, IgG(1) and IgG(2a) levels increased. The scratch count increased significantly in both the WBB6F1-W/W-v mice and C.B.17/Icr-scid mice when they were co-housed with skin-lesioned NC/Nga mice, raised under conventional conditions. These results show that IgE overproduction results from itch-associated scratching-induced dermatitis in NC/Nga mice.