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Always one step ahead: How pathogenic bacteria use the type III secretion system to manipulate the intestinal mucosal immune system.

Vossenkämper A, Macdonald TT, Marchès O - J Inflamm (Lond) (2011)

Bottom Line: The intestinal immune system and the epithelium are the first line of defense in the gut.Constantly exposed to microorganisms from the environment, the gut has complex defense mechanisms to prevent infections, as well as regulatory pathways to tolerate commensal bacteria and food antigens.The organisms that employ a type III secretion system use a molecular syringe to deliver effector proteins into the cytoplasm of host cells.

View Article: PubMed Central - HTML - PubMed

Affiliation: Centre for Immunology and Infectious Disease, Blizard Institute of Cell and Molecular Science, Barts and the London School of Medicine and Dentistry, London, UK. a.vossenkaemper@qmul.ac.uk.

ABSTRACT
The intestinal immune system and the epithelium are the first line of defense in the gut. Constantly exposed to microorganisms from the environment, the gut has complex defense mechanisms to prevent infections, as well as regulatory pathways to tolerate commensal bacteria and food antigens. Intestinal pathogens have developed strategies to regulate intestinal immunity and inflammation in order to establish or prolong infection. The organisms that employ a type III secretion system use a molecular syringe to deliver effector proteins into the cytoplasm of host cells. These effectors target the host cell cytoskeleton, cell organelles and signaling pathways. This review addresses the multiple mechanisms by which the type III secretion system targets the intestinal immune response, with a special focus on pathogenic E. coli.

No MeSH data available.


Related in: MedlinePlus

Follicles and PP are the inductive site for the mucosal immune response. Micrograph of a human ileal lymphoid follicle stained with hematoxylin & eosin. The follicle is covered by M-cells which form the follicle-associated epithelium (FAE). Underneath the dome area which holds dendritic cells, is a B cell follicle, surrounded by a T cell-rich zone. Adjacent to the follicle are microvilli. LP = lamina propria.
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Figure 1: Follicles and PP are the inductive site for the mucosal immune response. Micrograph of a human ileal lymphoid follicle stained with hematoxylin & eosin. The follicle is covered by M-cells which form the follicle-associated epithelium (FAE). Underneath the dome area which holds dendritic cells, is a B cell follicle, surrounded by a T cell-rich zone. Adjacent to the follicle are microvilli. LP = lamina propria.

Mentions: GALT is comprised of the appendix, single lymphoid follicles (Figure 1) in the small and large intestine, and the Peyer's patches (PP). The latter are clusters of follicles and have a distinct architecture with germinal centers containing B cells and follicular dendritic cells (DCs) which are surrounded by areas with T cells and macrophages [2]. PP are covered by specialized micro-folded epithelial cells, the M-cells, which make up the follicle-associated epithelium (FAE). This epithelium forms the interface between the luminal microorganisms and the immune cells of the GALT [4]. PP have no afferent lymph vessels and antigens are received directly from the intestinal lumen. After the uptake of luminal material by endocytosis and phagocytosis, the M-cells deliver antigens and microbes to antigen-presenting cells in the subepithelial dome of the PP, which subsequently present them to PP T cells [2]. PP DCs also directly sample bacteria from the intestinal lumen by sending protrusions through the epithelial layer without disrupting epithelial integrity [5]. Therefore, follicles and PP are an inductive site where microorganisms are sensed and the appropriate immune response is initiated [4]. In contrast, the lamina propria is an effector site; after activation in PP, DCs migrate to the mesenteric lymph nodes where they present antigens to B and T cells and the immune response is amplified. Via expression of homing molecules, mainly the integrin alpha4beta7 and CCR9, the lymphocytes are then able to re-enter the mucosal site where they contribute to immune defense along the entire length of the intestine [6].


Always one step ahead: How pathogenic bacteria use the type III secretion system to manipulate the intestinal mucosal immune system.

Vossenkämper A, Macdonald TT, Marchès O - J Inflamm (Lond) (2011)

Follicles and PP are the inductive site for the mucosal immune response. Micrograph of a human ileal lymphoid follicle stained with hematoxylin & eosin. The follicle is covered by M-cells which form the follicle-associated epithelium (FAE). Underneath the dome area which holds dendritic cells, is a B cell follicle, surrounded by a T cell-rich zone. Adjacent to the follicle are microvilli. LP = lamina propria.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3094202&req=5

Figure 1: Follicles and PP are the inductive site for the mucosal immune response. Micrograph of a human ileal lymphoid follicle stained with hematoxylin & eosin. The follicle is covered by M-cells which form the follicle-associated epithelium (FAE). Underneath the dome area which holds dendritic cells, is a B cell follicle, surrounded by a T cell-rich zone. Adjacent to the follicle are microvilli. LP = lamina propria.
Mentions: GALT is comprised of the appendix, single lymphoid follicles (Figure 1) in the small and large intestine, and the Peyer's patches (PP). The latter are clusters of follicles and have a distinct architecture with germinal centers containing B cells and follicular dendritic cells (DCs) which are surrounded by areas with T cells and macrophages [2]. PP are covered by specialized micro-folded epithelial cells, the M-cells, which make up the follicle-associated epithelium (FAE). This epithelium forms the interface between the luminal microorganisms and the immune cells of the GALT [4]. PP have no afferent lymph vessels and antigens are received directly from the intestinal lumen. After the uptake of luminal material by endocytosis and phagocytosis, the M-cells deliver antigens and microbes to antigen-presenting cells in the subepithelial dome of the PP, which subsequently present them to PP T cells [2]. PP DCs also directly sample bacteria from the intestinal lumen by sending protrusions through the epithelial layer without disrupting epithelial integrity [5]. Therefore, follicles and PP are an inductive site where microorganisms are sensed and the appropriate immune response is initiated [4]. In contrast, the lamina propria is an effector site; after activation in PP, DCs migrate to the mesenteric lymph nodes where they present antigens to B and T cells and the immune response is amplified. Via expression of homing molecules, mainly the integrin alpha4beta7 and CCR9, the lymphocytes are then able to re-enter the mucosal site where they contribute to immune defense along the entire length of the intestine [6].

Bottom Line: The intestinal immune system and the epithelium are the first line of defense in the gut.Constantly exposed to microorganisms from the environment, the gut has complex defense mechanisms to prevent infections, as well as regulatory pathways to tolerate commensal bacteria and food antigens.The organisms that employ a type III secretion system use a molecular syringe to deliver effector proteins into the cytoplasm of host cells.

View Article: PubMed Central - HTML - PubMed

Affiliation: Centre for Immunology and Infectious Disease, Blizard Institute of Cell and Molecular Science, Barts and the London School of Medicine and Dentistry, London, UK. a.vossenkaemper@qmul.ac.uk.

ABSTRACT
The intestinal immune system and the epithelium are the first line of defense in the gut. Constantly exposed to microorganisms from the environment, the gut has complex defense mechanisms to prevent infections, as well as regulatory pathways to tolerate commensal bacteria and food antigens. Intestinal pathogens have developed strategies to regulate intestinal immunity and inflammation in order to establish or prolong infection. The organisms that employ a type III secretion system use a molecular syringe to deliver effector proteins into the cytoplasm of host cells. These effectors target the host cell cytoskeleton, cell organelles and signaling pathways. This review addresses the multiple mechanisms by which the type III secretion system targets the intestinal immune response, with a special focus on pathogenic E. coli.

No MeSH data available.


Related in: MedlinePlus