GI Immunology Flashcards
How does the small intestine differ from the large intestine?
SI - villi and crypts, goblet cells, paneth cells, peyers patches for nutrient absorption.
LI- higher bacterial load, only crypts no villi, no paneth cells, enterocytes do defence, lots of goblet cells and mucus and no peyers patches.
What is the function of the intestinal immune system?
Mixture of specialised immune structures and cells that capture antigens, initiate the local immune response and carry out effector functions to clear any infection.
What do peyers patches and lymphoid follicles do?
Capture antigens and initiation of immune system.
How can dendritic cells capture antigens from the gut lumen?
They extend processes across the epithelium and grab them.
What is the anatomy of a peyers patch?
There is a subepithelial dome, holding a terminal centre and follicles. There are efferent lymphatics leading out from it. The gut epithelial covering of the peyers patch contains M cells with characteristic membrane ruffles.
What do gut M cells do?
Take up an antigen from the lumen by endocytosis and phagocytosis. The antigen is then transported across the cell in vesicles and released at the basal surface. The antigen then binds to dendritic cells which present them to activate T cells.
What two types of lymphoid tissue do we have in the gut?
What do both contain?
Where do they drain?
Organised and isolated lymphoid follicles.
Organised - large number of B cells and M cells.
Isolated - B cells only.
Both drain to mesenteric lymph nodes.
How do T cells enter peyers patches?
They enter from the blood guided by the homing receptors CCR7 and L-selectin.
When they encounter antigen in the The peyers patches and become activated by dendritic cells.
What happens to CCR7 when T cells enter peyers patches?
Once activated in the GALT, T cells lose CCR7 and so can no longer recirculate.
What happens to T cells that have been activated in the mesenteric lymph nodes?
Drain via mesenteric lymph nodes into the thoracic duct and return to the gut via the blood stream. Activated T cells expressing alpha4beta7 integrins and CCR9 home to the lamina propria and intestinal epithelium.
What is the humoral intestinal response?
IgA makes up the vast majority of the antibodies, then IgM and then IgG, this is a reversal of the systemic humoral response.
What is the gut epithelium?
What cells does the gut epithelia consist of?
Polarised columnar monolayer, spreading the microbiota from the lamina propria?
Consist of: enteroabsorptive cells, goblet cells, Neuroendocrine cells, M cells and paneth cells with tight junctions in between them.
