Extracellular pH Controls Chemotaxis of Neutrophil Granulocytes by Regulating Leukotriene B Production and Cdc42 Signaling.

Neutrophil granulocytes are the first and robust responders to the chemotactic molecules released from an inflamed acidic tissue. The aim of this study was to elucidate the role of microenvironmental pH in neutrophil chemotaxis. To this end, we used neutrophils from male C57BL/6J mice and combined live cell imaging chemotaxis assays with measurements of the intracellular pH (pH) in varied extracellular pH (pH). Observational studies were complemented by biochemical analyses of leukotriene B (LTB) production and activation of the Cdc42 Rho GTPase. Our data show that pH of neutrophils dose-dependently adapts to a given pH of the extracellular milieu. Neutrophil chemotaxis toward C5a has an optimum at pH ∼7.1, and its pH dependency is almost parallel to that of LTB production. Consequently, a shallow pH gradient, resembling that encountered by neutrophils during extravasation from a blood vessel (pH ∼7.4) into the interstitium (pH ∼7.2), favors chemotaxis of stimulated neutrophils. Lowering pH below pH 6.8, predominantly affects neutrophil chemotaxis, although the velocity is largely maintained. Inhibition of the Na/H exchanger 1 (NHE1) with cariporide drastically attenuates neutrophil chemotaxis at the optimal pH irrespective of the high LTB production. Neutrophil migration and chemotaxis are almost completely abrogated by inhibiting LTB production or blocking its receptor (BLT1). The abundance of the active GTP-bound form of Cdc42 is strongly reduced by NHE1 inhibition or pH 6.5. In conclusion, we propose that the pH dependence of neutrophil chemotaxis toward C5a is caused by a pH-dependent production of LTB and activation of Cdc42. Moreover, it requires the activity of NHE1.