S100A9 and pustular psoriasis: SAA reflects inflammation, which may be caused by locally and/or systematically produced IL-1β and IL-6, as well as IL-36 [29]. Additionally, S100A8, A9, and A15 may be upregulated in response to the inflammatory milieu in pustular psoriasis. In the current study, immunohistochemistry revealed the expression of both S100A8 and S100A9 in the epidermis, as well as mononuclear cell infiltration in the upper dermis, suggesting that mechanical stimuli induce the expression of S100A8 and S100A9.