FIGURE 3 Involvement of matrix metalloproteinases (MMPs) and interleukin (IL)-8 during human airway epithelial regeneration in the nude mouse xenograft model. During the different steps of human airway epithelium regeneration, a progressive decrease in IL-8 expression and secretion, associated with a progressive increase in MMPs' expression and secretion, can be observed. When the airway epithelium is fully differentiated, MMPs exhibit an exclusive expression at the apical part of the epithelium, and incubation with MMP inhibitors leads to an abnormal epithelial differentiation attested by immature and mature squamous metaplasia with areas of basal cell hyperplasia. TIMP: tissue inhibitor of matrix metalloproteinase. Scale bars = 35 µm. Reproduced with modification from [19] with permission from the publisher.