Acidic pH promotes degranulation and reduces oxidative stress in human primary neutrophils

Chronic wounds represent an increasing global health burden for both patients and healthcare systems. These non-healing lesions frequently result in amputation and are particularly prevalent among individuals with diabetes. Hallmarks of chronic wounds include a prolonged inflammatory phase characterized by sustained neutrophil infiltration, excessive formation of neutrophil extracellular traps (NETs), and an elevated alkaline tissue pH. Emerging evidence suggests a link between pH and wound healing, with acidic conditions being more favorable for tissue repair. Here, we investigated the pH-dependent modulation of primary neutrophil functions, including viability, reactive oxygen species (ROS) production, NET formation, and exocytosis. Neutrophils cultured in media with pH values ranging from 6.1 to 8.4 exhibited no significant differences in viability. In contrast, acidic conditions suppressed ROS production and NET formation in a pH-dependent manner, whereas alkaline conditions caused responses comparable to those observed at physiological pH (7.4). Furthermore, levels of antioxidant enzymes were markedly increased under acidic conditions following phorbol 12-myristate 13-acetate (PMA) stimulation. Notably, alkaline pH promoted granule polarization in neutrophils, thereby impairing exocytosis. In contrast, acidic conditions (pH < 7.0) reduced granule polarization and enhanced the release of granule-associated proteins upon PMA stimulation. Pharmacological inhibition of degranulation confirmed that these effects were mediated by neutrophil exocytosis. In summary, extracellular pH critically modulates neutrophil effector functions and may contribute to the distinct healing dynamics observed in acute versus chronic wounds. See also the graphical abstract(Fig. 1).