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 focused on HLA-DRA molecule’s contribution to the effect of airway epithelium on T-cell proliferation. METHODS: HLA-DRA expression and its dynamics during airway epithelial differentiation were assessed in human tissues (immunohistochemistry/immunofluorescence) and air-liquid interface (ALI) cultures (TaqMan qPCR, Western blotting, immunofluorescence). We employed a co-culture model to evaluate the regulatory effect of differentiated airway epithelium on T-cell proliferation, with HLA-DRA’s role tested via neutralizing antibodies. The impact of cigarette smoke extract (CSE) on HLA-DRA and T-cell proliferation was examined. We further explored the therapeutic potential of restoring HLA-DRA by overexpressing its transcriptional regulator, POU domain class 2–associating factor 1(POU2AF1, also known as OCA-B or BOB.1/OBF.1). We also validated key findings using public single-cell RNA sequencing data. FINDINGS: Both in vivo and in vitro analyses confirmed that HLA-DRA expression is significantly upregulated during HAEC’s differentiation, with high levels detected in apical ciliated and secretory cells but minimal in basal cells. In the co-culture model, well-differentiated HAECs (ALI-day 21) potently suppressed the proliferation of pre-activated T cells, whereas undifferentiated cells (ALI-day 0) did not. This immunosuppressive effect was contact-dependent and was partially but significantly reversed by pre-treating HAECs with anti-HLA-DRA blocking antibodies. Exposure to CSE downregulated HLA-DRA expression in differentiated HAECs and, concurrently, attenuated their capacity to inhibit T cell proliferation. CSE reduced the expression of the transcription factor POU2AF1, and lentiviral overexpression of POU2AF1 partially rescued HLA-DRA expression in smoke-exposed epithelium. CONCLUSIONS: Our findings indicate a novel immunoregulatory function of airway epithelium, wherein HLA-DRA partially mediates the contact-dependent suppression of activated T cell proliferation, which may contribute to mucosal immune balance. Cigarette smoke disrupts this “epithelial brake” mechanism via downregulation of the POU2AF1–HLA-DRA axis, promoting excessive T cell expansion. These results implicate the POU2AF1–HLA-DRA axis in smoking-associated airway inflammation and highlight its potential as a therapeutic target for immune modulation in chronic airway diseases.