In addition, the polymeric immunoglobulin receptor (pIgR)/secretory component (SC) system, which ensures the transcytosis and release of polymeric immunoglobulins into mucosal secretions, witnessing epithelial polarization, is also defective in COPD (Gohy et al, 2014; Carlier et al, 2020), with decreased epithelial pIgR expression (Gohy et al, 2014) and local S-IgA deficiency in small airways (Polosukhin et al, 2011, 2017). Here, PIGR is linked to hyperinsulinemic hypoglycemia, familial, 4.