The gut as a lymphoepithelial organ: The role of intestinal epithelial cells in mucosal immunity

Abstract

Mucosal surfaces covered by a layer of epithelial cells represent the largest and most critical interface between the organism and its environment. The barrier function of mucosal surfaces is performed by the epithelial layer and immune cells present in the mucosal compartment. As recently found, epithelial cells, apart from their participation in absorptive, digestive and secretory processes perform more than a passive barrier function and are directly involved in immune processes. Besides the well known role of epithelial cells in the transfer of polymeric immunoglobulins produced by lamina propria B lymphocytes to the luminal content of mucosals (secretory Igs), these cells were found to perform various other immunological functions, to interact with other cells of the immune system and to induce an efficient inflammatory response to microbial invasion: enzymic processing of dietary antigens, expression of class I and II MHC antigens, presentation of antigens to lymphocytes, expression of adhesive molecules mediating interaction with intraepithelial lymphocytes and components of extracellular matrix, production of cytokines and probable participation in extrathymic T cell development of intraepithelial lymphocytes. All these functions were suggested to influence substantially the mucosal immune system and its response. Under immunopathological conditions, e.g. during infections and inflammatory bowel and celiac diseases, both epithelial cells and intraepithelial lymphocytes participate substantially in inflammatory reactions. Moreover, enterocytes could become a target of mucosal immune factors. Mucosal immunosurveillance function is of crucial importance in various pathological conditions but especially in the case of the most frequent malignity occurring in the intestinal compartment, i.e. colorectal carcinoma. Proper understanding of the differentiation processes and functions of epithelial cells in interaction with other components of the mucosal immune system is therefore highly desirable.

Change of intestinal mucosa barrier function in the progress of non-alcoholic steatohepatitis in rats

“…Intestinal mucosa barriers include mechanical barrier, chemical barrier, immunologic barrier and biology barrier [18][19][20][21] , any damage of these barriers will damage intestinal mucosa barrier function. In this study, we used plasma D-xylose, endotoxin and intestine mucus sIgA to evaluate the intestinal mucosa barrier function in rats with NASH and to observe its change in NASH rats.…”

Molecular and Cellular Basis of Microflora-Host Interactions1,

“…The gut epithelium, apart from its participation in absorptive, digestive, and secretory processes, does not just act as a passive barrier but plays a major role in protection through interactions with the immune system (5). The small intestinal epithelium consists of 4 cell types, the absorptive enterocytes, the goblet cells, the enteroendocrine cells, and the Paneth cells in the crypts, whereas in the large intestine, Paneth cells are lacking.…”

“…Mucosal surfaces of the gut represent the main sites in which environmental microorganisms and antigens (Ag) 5 interact with the host. Sentinel cells including epithelial cells, macrophages, and intraepithelial dendritic cells (DCs) continuously sense the environment and coordinate defenses for the protection of mucosal tissues.…”

Mucosal Immunity: Its Role in Defense and Allergy

“…Epithelial cells respond to proinflammatory cytokines by synthesizing or producing immunologically active proteins. Epithelial line cells, constitutively or after stimulation, produce various cytokines (TGF-β, IL-1, IL-6, IL-8, IL-10 and others), trefoil factors and antimicrobial peptides (tables 2, 3) [5, 10, 12, 13]. …”

“…The mucosal immunity system fulfills the following basic tasks: (1) protection from harmful microbial pathogens (anti-infectious role), (2) barrier against penetration of infectious and immunogenic components present on the mucosas into the circulation and thus into the inner environment of the organism (barrier function), (3) low reactivity to harmless antigens present on mucosal surfaces (‘oral or mucosal tolerance’), (4) maintenance of mucosal homeostasis (immunoregulatory function) [2, 3, 4, 5]. …”