PIGR and chronic obstructive pulmonary disease: Several studies have also investigated the role of mucosal secretory IgA (SIgA) and COPD severity.[5,17–19] Abnormalities in the epithelial morphology have been shown to be associated with diminished SIgA levels through alterations in expression of the polymeric immunoglobulin receptor leading to increased risk for bacterial invasion, chronic inflammation and ultimately fibrotic remodeling,[17,18] particularly within the small airways.[17,19] It is possible that subnormal total IgA serum levels could be indicative of depressed SIgA levels elsewhere throughout the body.