Introduction: Using an air-liquid interface (ALI) model to culture primary human bronchial epithelial cells (phBECs), the avian-type flu receptor was expressed at the highest level in phBECs from a very severe COPD patient in which differentiation was impaired compared to those from COPD patients of less severe stages and non-COPD controls (Nakayama M et al. Front Microbiol 2023). Thus, we hypothesized that immature phBECs had increased expression of virus receptors, leading to increased viral replication. Aims: Evaluate the correlation between the degree of differentiation of phBECs and i) expression levels of avian-type flu/SARS-CoV-2 receptor, and ii) virus replication. Materials and Methods: PhBECs from 9 donors (healthy n=2, COPD n=4, asthma n=3), passage 5, were cultured at ALI for 28 days. Immunohistochemistry of the avian-type flu receptor (?2,3-linked sialic acid), angiotensin converting enzyme 2 and transmembrane serine protease 2 (ACE2 and TMPRSS2, essential for SARS-CoV-2 entry), and nucleus staining were performed. PhBECs were infected with H5N1 avian flu/SARS-CoV-2 (alpha), and apical washes were collected on the next day. Results: Differentiation defined by higher nuclear density had an inverse correlation with the percentage of cells positive for the avian-type flu receptor, ACE2 and TMPRSS2 (l r l>0.6; p=0.096, 0.026 and 0.0004, respectively). Virus titers did not have a strong correlation (l r l<0.5). Conclusion: Immature phBECs may facilitate the attachment of avian influenza viruses and SARS-CoV-2. However, virus replication was not directly affected by higher expression of viral receptors.