Differences Between Oral Neutrophils and Neutrophils Isolated From the Blood of Healthy Donors

The morphological and viscoelastic properties of blood neutrophils and neutrophils isolated from the oral cavity of the same donor were compared using scanning ion conductance microscopy. It was found that cell morphology, including morphometric parameters (height, diameter, and cell volume), did not differ significantly. However, the elasticity of the membrane-cytoskeletal complex was primarily determined by the cell compartment and its functional state (e.g., migration or adhesion) rather than the neutrophils' ecological niche (blood or oral cavity). The ability of blood neutrophils and oral neutrophils to produce reactive oxygen species (ROS) was assessed using luminol-dependent chemiluminescence. Neutrophils isolated from the oral cavity demonstrated a significantly higher ROS-producing activity compared to blood neutrophils from the same donor. Additionally, oral neutrophils exhibited high variability in ROS production levels, even within the same donor on different days of collection. When comparing the stimulation of ROS production in blood and oral neutrophils exposed to S. aureus 2879M, the cells displayed opposing responses: blood neutrophils were stimulated by Staphylococci, whereas oral neutrophils were inhibited. This response persisted when cells were stimulated by Staphylococci preincubated with saliva. The sequential addition of unfiltered saliva to neutrophils and Staphylococci enhanced this trend, while filtered oral fluid attenuated it. For the first time, it was established that saliva without bacteria (filtered through bacterial filters) suppresses the production of ROS by both blood neutrophils and oral neutrophils, most likely indicating an anti-inflammatory effect of saliva.