Fig. 4.

Directional cell migration along pH gradients. a In a normal wound (left half), epidermal keratinocytes and dermal fibroblasts migrate towards the more alkaline pH_e in the center of the wound in order to close it. In a chronic wound (right half), a quite acidic pH at the wound margin prevents keratinocytes and fibroblasts from migrating into the wound. Instead, neutrophils are attracted by the low pH. Once inside the wound area, their presence including the local secretion of inflammatory mediators fuels the inflammatory process and thus prevents wound healing. b In general, neutrophils migrate towards inflammatory sites that typically are acidic (left). Microvascular endothelial cells also migrate to tissue areas with an acidic pH value, while metastatic tumor cells migrate away from the acidic tumor tissue to regions with a physiological pH value near blood and lymph vessels. Please see the section on pH taxis for further details and references