Abstract
T cells play a central role in host protection against respiratory pathogens, but a maladaptive T cell response can lead to pulmonary diseases. Previous studies have examined T cells from the lungs captured via bronchoalveolar lavage (BAL), endobronchial brushings, or biopsies. However, whether these different approaches are capturing distinct T cell phenotypes and/or clonotypes remains unclear. Here, using single cell RNA- and T cell receptor (TCR)-sequencing, we report unique phenotypes and clonotypes of T cells isolated via BAL versus endobronchial brushings in healthy controls (HCs) and allergic asthmatics (AAs). The most significant difference in T cell subset abundance between AAs and HCs was the enrichment of CD4 T helper type 2 (TH2) cells when comparing endobronchial brush samples (OR = 20.8, P = 0.004), but not when examining BAL (OR = 1.8, P = 0.38), indicating differences in the T cell subsets captured from the BAL versus airway mucosa. In further support of this observation, comparing the BAL and brush T cells across all subjects revealed an up-regulation of resident-memory T (TRM) cell markers (i.e. ITGAE, CD69) in brush T cells in both CD4 and CD8 lineages. In contrast, BAL CD8 and CD4 T cells exhibited an enriched type I and II interferon signature compared to brush T cells. We validated these findings by generating an independent cohort from publicly available single cell RNA-sequencing data of BAL and brush T cells. Lastly, leveraging the paired samples from our derivation cohort, we performed TCR repertoire analysis, revealing that brush T cells contained expanded TCR clones that were in low abundance or absent in the BAL. Expanded T cell clones from the brush expressed high levels of TRM cell markers, suggesting the airway mucosa is enriched for TRM cells with unique TCR specificity. In sum, sampling T cells via BAL versus airway brushings yielded distinct T cell phenotypes and clonotypes with important implications for future research in lung immunology.