Dysfunction of neutrophils in patients with cystic fibrosis (CF) is best characterized in bronchoalveolar lavage (BAL), whereas peripheral blood neutrophils are less examined, and the results are contradictory, especially in younger populations. Therefore, this work aimed to study functional and phenotypic changes in circulating neutrophils in children with CF. The study included 19 CF children (5–17 years) and 14 corresponding age-matched healthy children. Isolated neutrophils were cultured either alone or with different stimuli. Several functions were studied: apoptosis, NET-osis, phagocytosis, and production of reactive oxygen species (ROS), neutrophil elastase (NE), and 11 cytokines. In addition, the expression of 20 molecules involved in different functions of neutrophils was evaluated by using flow cytometry. CF neutrophils showed reduced apoptosis and lower production of NE and IL-18 compared to the healthy controls, whereas IL-8 was augmented. All of these functions were further potentiated after neutrophil stimulation, which included higher ROS production and the up-regulation of CD11b and IL-10 expression. NET-osis was higher only when neutrophils from moderate–severe CF were treated with Pseudomonas aeruginosa, and the process correlated with forced expiratory volume in the first second (FEV1). Phagocytosis was not significantly changed. In conclusion, circulating neutrophils from children with CF showed fewer impaired changes in phenotype than in function. Functional abnormalities, which were already present at the baseline levels in neutrophils, depended on the type of stimuli that mimicked different activation states of these cells at the site of infection.

Sitagliptin is a dipeptidyl peptidase-4 (DPP-4) inhibitor used to treat type 2 diabetes. However, several studies have demonstrated its anti-inflammatory and immunomodulatory properties. The aim of this study was to investigate the effect of sitagliptin on the functional and phenotypic properties of human neutrophils under normal (NG, 5.5 mM)- and high (HG, 22 mM)-glucose conditions in vitro. Neutrophils were pretreated with varying concentrations of sitagliptin and stimulated with phorbol-12-myristate-13-acetate (PMA), N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP), calcium ionophore (CaI), or opsonized zymosan (OpZym). Survival, phenotypic, and functional characteristics were then assessed. Our results showed that sitagliptin was non-cytotoxic to neutrophils even at very high concentrations. It decreased the production of reactive oxygen species (ROS) and neutrophil extracellular traps (NETs), generally following a stimulus- and concentration-dependent pattern. The effect was more pronounced under HG conditions. Furthermore, sitagliptin showed a significant ROS-scavenging effect in a cell-free system. It also rapidly altered the expression of surface markers in both resting and fMLP-stimulated neutrophils, typically upregulating CD10, CD16, CD62L, CD63, CD88, CD89, and PD-L1, and downregulating CD11b/CD18, CD66b, and CD182, a phenotype consistent with a dampened, less-primed activation state of these cells. In conclusion, sitagliptin exhibited marked antioxidative/ROS-scavenging activity in neutrophil cultures and induced a coordinated shift in neutrophil phenotype, accompanied by suppression of NETosis under both NG and HG conditions. Collectively, these data support the view that neutrophils may constitute an additional cellular target contributing to sitagliptin’s anti-inflammatory and immunomodulatory profile.