In a study by Kobayashi et al., matrix metalloproteinase-9 (MMP-9, gelatinase B) was reported to be elevated in the blister fluid using zymography, and MMP-9, secreted by PMN on the dermal side of the dermoepidermal junction, was postulated to migrate from the lesion of intensive vasculitis and to cause blister formation by degrading basement membrane components such as type VII collagen [10]. Here, MMP9 is linked to vasculitis.