LILRB1 Modulates Neutrophil Migration, NETosis, and Inflammation in Drug-Resistant Pseudomonas aeruginosa-Associated Bronchiectasis

Background: Patients with drug-resistant Pseudomonas aeruginosa ( P. aeruginosa )-associated bronchiectasis often exhibit persistent neutrophilic airway inflammation. The immunomodulatory receptor leukocyte immunoglobulin-like receptor B1 (LILRB1) is known to function as an inhibitory checkpoint in immune responses, yet its specific role in regulating neutrophil function in drug-resistant P. aeruginosa -associated bronchiectasis remains incompletely understood. This study aimed to characterize the function of LILRB1 in this clinical context. Methods: Clinical samples were obtained from bronchiectasis patients with drug-resistant P. aeruginosa infection and control subjects. LILRB1 mRNA expression was quantified by reverse transcription-quantitative polymerase chain reaction (RT-qPCR), and soluble HLA-G (sHLA-G) levels were assessed by enzyme-linked immunosorbent assay (ELISA). Neutrophils isolated from peripheral blood were stimulated with a clinical isolate of drug-resistant P. aeruginosa . NETosis was evaluated using myeloperoxidase (MPO)/citrullinated histone H3 (CitH3) immunofluorescence staining and quantified via PicoGreen dsDNA assay. The modulatory effect of recombinant LILRB1 protein was examined in a Transwell co-culture system composed of neutrophils and P. aeruginosa -infected BEAS-2B bronchial epithelial cells, with neutrophil migration and inflammatory cytokine secretion assessed as outcome measures. Results: LILRB1 expression was significantly lower in patients with drug-resistant P. aeruginosa infection than in controls (P = 0.0384) and was inversely associated with disease severity, as indicated by the Bronchiectasis Severity Index (P = 0.0089), and with peripheral neutrophil counts (r = − 0.35, P = 0.044). Levels of sHLA-G in bronchoalveolar lavage fluid were elevated and showed an inverse correlation with LILRB1 expression. Treatment with recombinant LILRB1 protein significantly attenuated P. aeruginosa -induced neutrophil migration in the co-culture model, reducing the number of migrated cells from 4.43± 0.26× 10 4 to 2.75± 0.19× 10 4 . Furthermore, LILRB1 protein suppressed NETosis and significantly decreased the concentrations of IL1β, IL6, and IL8 in the co-culture supernatants. Conclusion: Our findings indicate that LILRB1 acts as a significant regulator of neutrophilic inflammation in drug-resistant P. aeruginosa -associated bronchiectasis. By dampening neutrophil migration, NETosis, and pro-inflammatory cytokine release, LILRB1 may represent a potential target for mitigating inflammation in this patient population.