Integrin-mediated entry and fibroblast-supported retention in memory B cell residency in allergic lungs

Introduction/Rationale: Allergic asthma is a chronic inflammatory disease of the airway driven by allergen-specific IgE antibodies. We recently identified lung-resident memory B cells (MBCs) as a major source of allergen-specific IgE in the airway. Compared to circulating MBCs, lung MBCs upregulate integrin subunits a4 and aL. Thus, we hypothesize that integrins mediate MBC entry into the lung where the lung stroma supports MBC residency and survival.

Methods: To disrupt integrin-mediated interactions, we i.v. administered blocking antibodies against integrins a4 and aL during sensitization in a mouse model of airway hypersensitivity. Lung B cells were identified by flow cytometry and i.v. CD45-labeling. Allergen-specific IgE was quantified by ELISA. To analyze the lung stroma, we performed single cell RNA-seq on FAC-sorted CD45- cells from sensitized and unsensitized lungs. Gene expression and cell-cell communication analyses were performed using Seurat v5 and CellChat, respectively.

Results: Blocking both integrins a4 and aL, but not a4 or aL alone, significantly reduced MBCs in the lung and increased MBCs in the lung vasculature, suggesting MBCs are stuck in the lung vasculature. Notably, integrin blockade also reduced antigen-specific IgE in the airway to undetectable levels. Cell-cell communication analyses on bioinformatically paired single cell RNA-seq data on the lung stroma and MBCs predicted interactions between MBCs and lung fibroblasts expressing extracellular matrix (ECM) proteins and MBC survival factors such as BAFF. Top upregulated gene pathways in fibroblasts after allergen sensitization also included ECM synthesis and integrin-mediated cell-cell interactions.

Conclusion: Altogether, these results support that MBCs enter the allergic lung via upregulation of select integrins and may be retained in an ECM-rich survival niche provided by activated fibroblasts. These findings provide a mechanism for lung-resident MBC formation in allergic asthma and potential targets for disrupting pathogenic IgE responses.