Stromal and immune cell interplay promotes neutrophilic inflammation in chronic rhinosinusitis with nasal polyps.

PURPOSE OF REVIEW: Chronic rhinosinusitis with nasal polyps (CRSwNP) is a heterogeneous inflammatory disorder, with neutrophilic inflammation representing a clinically challenging endotype due to its resistance to corticosteroids and biologics targeting type 2 responses. Single-cell RNA sequencing (scRNA-seq) studies are providing novel insights into the pathogenesis of CRSwNP, particularly the roles of neutrophils and stromal cells. This review discusses how scRNA-seq has inspired a new focus on stromal-immune cell crosstalk as a driver of neutrophilic inflammation. We emphasize the pathogenic contributions of fibroblasts, granzyme K-expressing (GZMK+) CD8+ T cells, and dysregulated cytokine networks such as interleukin (IL)-1β and C-X-C motif chemokine ligand (CXCL). Understanding these interactions is critical for developing endotype-specific therapies for refractory CRSwNP characterized by neutrophilic inflammation.

RECENT FINDINGS: ScRNA-seq has revealed a significant heterogeneity in neutrophils and stromal cell populations within CRSwNP, with distinct subpopulations exhibiting unique functional profiles. The IL-1β-activated indoleamine 2,3-dioxygenase 1-expressing (IDO1+) fibroblast subset drives neutrophilic inflammation in CRSwNP through secreting a number of CXCL chemokines. Lymphocyte antigen 6 family member D-expressing (LY6D+) club cells in nasal epithelium express high levels of S100 calcium binding protein A (S100A) 8 and S100A9, known as chemoattractants for neutrophils, under IL-1β stimulation. Fibroblast-derived CXCL12 recruits C-X-C motif chemokine receptor (CXCR) 4+GZMK+CD8+ T cells, establishing a feed-forward inflammatory loop. This cycle is driven by GZMK-mediated stromal activation, resulting in the secretion of potent neutrophil chemokines. Therapeutics targeting of IL-1β and CXCL12-CXCR4 signaling show potential for suppressing neutrophilic inflammation in CRSwNP.

SUMMARY: Stromal and immune cell interactions drive neutrophilic inflammation in CRSwNP. Targeting these cells and their signaling networks offers promising avenues for precision therapy, aiming to control neutrophilic inflammation, reduce associated polyp recurrence, and improve long-term disease outcomes.