Abstract
To date few studies have addressed the development and function of the porcine gastric mucosal immune system and this is a major limitation to understanding the immunopathogenesis of infections occurring in young pigs. The polymeric immunoglobulin receptor (pIgR) mediates the transport of secretory immunoglobulins until luminal surface of the gut mucosa and the aim of this study was to investigate the time course of pIgR expression and to determine its localization in three functionally different porcine gastric sites during the suckling period and after weaning. An additional goal was to investigate the time course expression of toll-like receptors (TLRs) in relation to pIgR expression. Gastric samples were collected from the cardiac-to-oxyntic transition (Cd), the oxyntic (Ox), and the pyloric (Py) regions in 84 pigs, slaughtered before weaning (14, 21 and 28 days of age; 23, 23 and 19 pigs, respectively) and 14 days post-weaning (42 days of age, 23 pigs). PIgR was expressed in the mucosa of all the three gastric sites, and its transcript levels were modulated during suckling and after weaning, with regional differences. PIgR expression increased linearly during suckling (P=0.019) and also increased post-weaning (P=0.001) in Cd, it increased post-weaning in Py (P=0.049) and increased linearly during suckling in Ox (P=0.036). TLRs expression was also modulated during development: in Cd, TLR2 increased linearly during suckling (P=0.003); in Ox, TLR2 decreased after weaning (P=0.038) while TLR4 increased linearly during suckling(P=0.008). The expression of TLR2, 3 and 4 in Ox was positively correlated with pIgR expression (P<0.001).Importantly, both pIgR protein and mRNA were localized, by immunohistochemistry and in situ hybridization, respectively, in the gastric glands of the lamina propria. These results indicate that pIgR is actively synthesized in the gastric mucosa and suggest that pIgR could play a crucial role in gastric mucosal immune defense of growing pigs.
Highlights
The mucosal immune system of the gastrointestinal tract plays a primary role in the interaction between the host and both commensal and potentially pathogenic microorganisms [1]
To gain insight into the role of the stomach in the defense against pathogens in young piglets, we hypothesized that the gastric mucosa is provided with the basic machinery of the innate and adaptive mucosal immune system
This hypothesis was supported by a previous report that described the distribution of the gastric-associated lymphoid tissue in conventional piglets [10]
Summary
The mucosal immune system of the gastrointestinal tract plays a primary role in the interaction between the host and both commensal and potentially pathogenic microorganisms [1]. A key element of the adaptive mucosal immune system is the polymeric immunoglobulins (pIgs). They are produced by plasma cells in the lamina propria and are actively transcytosed to the lumen through the epithelial cell by the polymeric immunoglobulin receptor (pIgR) [4]. Mucosal immune responses in the stomach have been largely neglected, often as they were considered to be of minor importance in relation to gut diseases, due to the inhospitable microbial environment and to the shorter exposure time to the feed, in comparison with other regions of the gastrointestinal tract. To the best of our knowledge, no previous studies have characterized the expression of pIgR during gastric mucosa development in the suckling period and after weaning in pigs
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