HLA-DRA-Mediated Inhibition of T-Cell Proliferation by Differentiated Airway Epithelium and Its Disruption in Smoking- Associated Airway Inflammation

Background: HLA-DRA molecule is expressed in human airway epithelial cells (HAECs), but its specific functions remain unclear. This study mainly concentrated on HLA-DRA molecule's contribution to the effect of airway epithelium on T cell proliferation. Methods: We examined the expression of HLA-DRA molecule and its trend over time via staining of human in-vivo samples, multi-dimensional analysis including TaqMan assays, Western blotting and staining of in-vitro airway epithelial organoid model. Next, we examined the regulatory effect of HAECs on T cell proliferation via co-culture model. Then, HLA-DRA molecule was blocked by neutralizing antibodies to determine whether HLA-DRA could play a role in above effect. After that, cigarette smoking extract (CSE) induced changes in HLA-DRA expression level and T cell proliferation was assessed to explore the role of HLA-DRA in smoking-associated airway inflammation and identify potential therapeutic targets. Besides, Single-cell RNA sequencing data from GEO were analyzed to validated above issues at a unicellular level. Results: The expression of HLA-DRA in airway epithelium and its up-regulation during differentiation were validated both in-vivo and in-vitro. Well-differentiated HAECs could inhibit pre-activated T cell proliferation, and HLA-DRA molecule partially mediated the inhibitory effect. CSE downregulated HLA-DRA expression, and attenuated the inhibitory effect of HAECs for T cell proliferation. Overexpression of POU2AF1, a known transcription factor of HLA-DRA, partly rescued CSE-induced HLA-DRA down-regulation. Conclusions: We identify an HLA-DRA-mediated pathway whereby HAECs physiologically inhibit active T cell proliferation. Smoking subverts this checkpoint via POU2AF1-HLA-DRA axis disruption, promoting T cell hyperproliferation and unwanted airway inflammation.