Tracheal and bronchial polymeric immunoglobulin secretory immune system (PISIS) development in a porcine model

Polymeric immunoglobulins (pIgs) mucosal secretion is mediated by the pIg secretory immune system (PISIS), which is composed of J-chain (JC) and antibody (IgM/IgA) producing cells (JC-AbPC), pIg receptor (pIgR) epithelial cell expression and the efficient release of secretory Igs (SIgs) to the mucosal lumen. A poor development or disturbances in this system may cause higher infection susceptibility, as observed in young and elderly people. In spite of this system's importance, few detailed studies regarding its development have been described in the lower respiratory tract of humans. Because the porcine model has been reported as an option for translational medicine to humans, we studied the tracheal and bronchial PISIS development in healthy, non-vaccinated, SPF, miniature Vietnamese pigs from birth to adulthood using immunohistochemistry and ELISAs. Our results demonstrated that pIgR was present at birth, and its expression increased with age. In contrast, JC-AbPC were low in neonatal pigs; however, colostrum was a source of IgM, SIgA, total IgA and IgG in respiratory secretions (trachea and bronchoalveolar lavages, nasal secretion and saliva) in piglets. JC-AbPC steadily increased in post-weaned, young and adult pigs, correlating with considerable increases in secretory and total Igs in the trachea and bronchi. These data suggest a compensatory role of maternal Igs at the respiratory mucosa in the absence of a structured PISIS before weaning. Furthermore, monomeric Igs (IgG and IgA) may also play an important role in respiratory protection and deserves a more thorough study.