PIGR and chronic obstructive pulmonary disease: The intriguing finding that upon SIgA-deficiency airway microbiota directly contribute to the pathogenesis of lung inflammation together with the aforementioned advancing loss of SIgA during disease progression in the airways of COPD patients directly suggest a so far underappreciated role of the pIgR/SIgA axis and related SIg-mediated immune exclusion of not only pathogens but as well commensals in the pathophysiology of CRD.