B33-21 Immune Cell Profiling Of Bronchiectasis Patients With Chronic Infection By Single-cell Sequencing

Rationale

Bronchiectasis is characterized by chronic airway inflammation and recurrent infections, yet the immunologic mechanisms underlying persistent bacterial colonization remain poorly defined. In particular, the interplay between chronic bacterial infection and host innate immune dysfunction has not been fully elucidated. This pilot study aimed to investigate how chronic bacterial presence in sputum influences systemic immune responses by comparing peripheral blood immune cell profiles using single-cell RNA sequencing (scRNA-seq). We hypothesized that chronic infection would induce distinct alterations in innate immune cell composition and apoptotic signaling pathways, potentially contributing to bacterial persistence.

Methods

This single-center prospective study included adults with CT-confirmed bronchiectasis: three with chronic bacterial presence in sputum and three controls without bacterial detection. Chronic infection was defined as isolation of the same bacteria at least twice ≥3 months apart within one year. Peripheral blood mononuclear cells were analyzed by single-cell RNA sequencing to assess immune cell gene expression differences.

Results

Of six enrolled patients, one with chronic infection was excluded due to insufficient specimen cellularity, leaving five for analysis. The case group (n = 2) had persistent Pseudomonas aeruginosa detection in sputum, while the control group (n = 3) had no history of bacterial detection. Single-cell RNA sequencing revealed significantly higher proportions of natural killer (NK) cells and monocytes—key innate immune components—in the case group, suggesting enhanced innate immune activation by bacterial exposure. However, expression of interferon-stimulated genes and chemokines, essential for bacterial clearance, was markedly reduced. Notably, analysis of the FAS ligand (FASLG)-FAS pathway, critical for NK cell-mediated apoptosis, showed significantly decreased FAS expression in CD14⁺ monocytes and dendritic cells (DCs) in the case group (Figure 1). This reduction may impair apoptotic clearance of infected cells, potentially facilitating persistent bacterial colonization.

Conclusion

In bronchiectasis, chronic bacterial colonization was associated with impaired innate immunity and reduced FAS expression, suggesting deficient apoptosis in response to bacteria. These results implicate impaired apoptotic signaling in persistent infection and may inform biomarker discovery and therapeutic strategies.

Figure 1. The involvement of the FASLG-FAS pathway in immune cell-mediated apoptosis. A. The inferred FASLG-FAS signaling pathway network at control group. B. Violin plot of the gene encoding FASLG in NK cells, C. Violin plot of the gene encoding FAS in CD14 monocytes, D. Violin plot of the gene encoding FAS in DC

This abstract is funded by: None