Flashcards in Mucosal Immunology of the GI tract Deck (30):
What lymphoid tissues are contained in the GI tract?
Peye's Patches in Small intestine
What are the physiological function of the GI tract?
Food digestion and absorption
Describe the structure of the cells of the gut barrier and what types of cells there are?
Polarised columnar monolayer of cells that separate the microbiota from the lamina propria
1. Enteroabsorptive cells
2. Goblet cells
3. Neuroendocrine cells
4. Paneth cells
5. M cells
What are the features of the small intestine?
Villi and crypts
Goblet cells- mucus
Paneth cells- defensins
Peyer’s Patches- antigen sampling and immune activation
What are the features of the large intestine?
Higher bacterial load
Only crypts no villi
No paneth cells
Enterocytes do defense
Lots of goblet cells and mucus
No Peyer’s patches
Where does the lymphatic system of the intestines go to?
To the Mesenteric Lymph node.
What is the layer between the epithelium called and what type of cells are found here?
The Lamina Propria. Immune cells are found here in Peyer's Patches.
What is the function of goblet cells?
To produce mucus
What is the function of Paneth cells?
Produce anti-microbial peptides such as Defensins
What is the function of Peyer's Pathces?
Antigen sampling and immune activation sites
What cell would be found in a Peyer's patch?
Lamina Propria effector T cells
IgA secreting plasma cells
Describe the structure of the colon?
Crypts present with no villi or Paneth cells. High presence of goblet cells
Describe the structure of the small intestine?
Arranged into crypts with villi. Immune cell present in the lamina propria in Peyer's patches. Panted cells cane found at the base of the crypts alongside goblet cells.
Describe how dendritic cells can capture the antigen in the gut?
Dendritic cells can extend their processes from the Peyer's path or across the epithelium to capture the antigen.
What type of cell covers the epithelial layer?
M cells - these cells have characterise membrane ruffles. Allows them to take up antigens from the gut.
The dendritic cels sit membrane to membrane with the M cells and allows them to capture antigen.s
Describe the process by which an M cell takes up an antigen and how it leads to activation of T cells?
M cells take up the anitgen by endocytosis and phagocytosis
The antigen is transported across the M cell to the basal surface and to the dendritic cell which sits membrane to membrane with the M cell.
The antigen is bound to the dendritic cell that activates T cells
Describe the organisation of the Lymphoid tissue in the gut?
Large number of B cell follicles in the gut.
The gut is exposed to microorganisms by the M cells
Lymphoid tissue ins the initiation site of the immune response.
Lymphoid tissues drain to the Mesenteric lymph nodes from were the intestinal immune response is initiated.
What receptor is on T cells and B cells that allow them to circulate the body?
What occurs when the T cells and B cells when they become activated?
They lose the CCR7 receptor and gain other receptors.
This prevents them from circulating the body
What is the adhesion molecule expressed on the T cells and the B cells which allows them to join onto the endothelium of the enterocytes?
Alpha 4 Beta 7
What is the antigen expressed by the endothelium that the Cell attach onto to allow cellular adhesion?
What chemokine is used in the small intestine to attach cell to it?
What does an activated T cell or B cell express?
Describe how the T cell or B cell moves from the blood vessel through to the Lamina propria?
The cell expresses alpha 4 Beta 7 which binds to MADCAM 1 - this allows movement thrgouh to the lamina propria
The cell is attacked to the lamina propria due to the use of chemokine CCL25
The cell them interacts with the epithelial cells via CCR10 and CCR9
What is the most common antibody in a healthy gut?
IgA is the highest and IgG is the lowest - this is the reverse of the systemic immune response.
Describe the action of IgA in the go tract and its structure?
IgA is a dimeric antibody, two antibodies are held together via a J chain.
The antibody coats the gut lumen and acts as an immune barrier to the gut.
Describe the process which IgA undergoes to coat the gut lumen?
IgA is secret from a plasma cell.
The IgA moves to the epithelial cells, where it interacts with a Poly-IgA receptor,
This accepts the cell into a vesicle via endocytosis
The receptor is cleaved to form the secretory component
IgA is released with a secretory component on the apical face of the epithelial cell.
What does the gut have within the epithelium to protect it?
Intraepithelial lymphocytes. These express Alpha 4 beta 7 intern which anchors them to the epithelium.
What is the mechanism of mucosal hypo responsiveness?
Anergy of antigen specific T cells (switching off)