First line of defense: the role of the intestinal epithelium as an active component of the mucosal immune system

Abstract

of the monolayer. Intestinal epithelial cells can be defined as playing an important role in both innate and adaptive immune responses. This review attempts to outline some of the mechanisms by which IECs participate in both these forms of defense. Role of IECs in innate mucosal immunityThe intestinal lumen, particularly that of the colon, contains a large variety of bacteria and bacterially derived products. 1,2 A number of "broadly-specific" defense mechanisms have evolved to guard against the risk of attack from invasive microorganisms. These mechanisms can be classified as intrinsic or extrinsic in nature. Intrinsic mechanisms of immunity are derived from the physical presence of an epithelial barrier and are dependent upon the unique structural properties exhibited by the IEC. Extrinsic defenses are defined as those processes which act outside the monolayer to resist microbial interaction with the mucosa. Intrinsic immunity: barrier functionThe formation of a selectively permeable epithelial barrier is essential in preventing the uncontrolled passage of pathogenic antigens from the external environment to the internal tissue. Establishment of the epithelial monolayer by contributing IECs is dependent upon a considerably high degree of intracellular and intercellular organization (for a review, see 3 ). Within each epithelial cell, structural integrity is maintained by the presence of a complex cytoskeletal network of microfilaments. These filaments vary in their composition and location. Actin-based filaments, for example, form rings at both the apical and basolateral poles of the cell, while intermediate filaments course through the cytoplasm and anchor at points of the plasma membrane. 4,5 Together, these structures are crucial in maintaining cellular polarity and in supporting points of cell-cell contact.

Porcine epidemic diarrhea virus infection induces NF-κB activation through the TLR2, TLR3 and TLR9 pathways in porcine intestinal epithelial cells

“…Data from previous studies have shown that differences occur in the immune functions of porcine epithelial cells and their interactions with other immune cell populations, compared with those from other species (Schierack et al, 2006). Epithelial cells play a pivotal role in coordinating host immune responses via production of several essential signalling molecules (such as cytokines and chemokines, as well as cell surface molecules), the expression of which is also regulated by NFkB (Moynagh, 2005;Pitman & Blumberg, 2000).…”

CCR6 has a non‐redundant role in the development of inflammatory bowel disease

“…In addition to its function as a physical barrier, the intestinal epithelium influences local immune responses through expression of adhesion molecules, costimulatory factors, chemokines and cytokines [44]. Constitutive CCL20 expression in the intestine can be up-regulated by inflammatory stimuli [25,26,43].…”

BOARD-INVITED REVIEW: Porcine mucosal immunity of the gastrointestinal tract1

“…However, before antigens reach the GALT, antigens must breach the IEC monolayer that separates the GALT from the intestinal lumen. The IEC monolayer provides both intrinsic and extrinsic barriers to potentially harmful pathogens and antigens (reviewed by Pitman and Blumberg, 2000). The intrinsic mechanism hinges on the establishment of a physical barrier via the highly organized IEC monolayer, which facilitates selective transfer of lumenal contents to the underlying GALT.…”