Skin-infiltrating neutrophils following exposure to solar-simulated radiation could play an important role in photoageing of human skin

Summary Background  The pathophysiology of photoageing of the skin has been studied extensively. Matrix metalloproteinases (MMPs) originating from keratinocytes and fibroblasts are thought to play a primary role in this process. Although neutrophils are potent producers of a wide array of proteolytic substances and are present in sunburned skin, their contribution to the pathophysiology of photoageing has been described only in murine studies. Objectives  To determine the role of neutrophils in photoageing of human skin. Methods  Healthy white-skinned volunteers were recruited and their sun-protected buttock skin was exposed to solar-simulated radiation (SSR) in dose–response and time-course studies. Punch biopsies were taken and the influx of neutrophils and the expression of neutrophil elastase and MMPs was studied using immunohistochemical techniques and in situ zymography. Results  Neutrophil elastase and MMPs were detected only in skin irradiated with erythemogenic doses (≥ 1 minimal erythema doses) of SSR. Immunohistochemical double staining demonstrated neutrophils to be the major source of MMP-1, MMP-8 and MMP-9. In situ zymography showed elastase, collagenase and gelatinase enzyme activity in those cells. Conclusions  Our study suggests that neutrophils participate in the process of photoageing of human skin as they infiltrate the skin and release enzymatically active elastase (neutrophil elastase), collagenase (MMP-1) and gelatinase (MMP-9).