Immunology Flashcards
(81 cards)
Why are mucosal tissues highly vulnerable?
Due to their fragility and permeability.
What type of lymphoid tissue is important in mucosal immunity?
Secondary.
Where do dendritic cells enter a lymph node?
Through afferent lymphatic vessels.
Where do T cells enter a lymph node?
Through blood.
What does it mean when it is said that the gut epithelium has an intimate relationship between mucosal epithelia and lymphoid tissue?
That they are very close and there are organised lymphoid structures unique to the mucosal site.
What are the main type of T cells present?
Activated/memory T cells predominate, also natural effector/regulatory T cells.
What 2 types of cells make the mucosa an immunoregulatory environment?
Inhibitory macrophages and tolerising dendritic cells.
What are the equivalents of lymph nodes in the small and large intestine?
Small: Peyer’s patch.
Large: isolated lymphoid follicle.
Other than these structures, where else are lymphocytes located in the mucosa?
Lamina propria and in the epithelium.
What are M cells and what do they cover?
They are specialised cells with characteristic membrane ruffles that let antigens in. They are part of the epithelial layer that covers Peyer’s patches.
Describe the 3 steps involving M cells and dendritic cells which cause activation of T cells.
- M cells take up antigen by endocytosis and phagocytosis.
- Antigen is transported across the M cells in vesicles and are released at the basal surface.
- Antigen is bound by dendritic cells, which activate T cells.
How is it possible for dendritic cells to capture antigens from the lumen of the gut?
They can extend their processes across the epithelial layer.
What are the 2 receptors on T cells that allow them to enter Peyer’s patches?
Homing receptors CCR7 and L-selectin.
After T cells have been activated by dendritic cells, where do they then go?
They drain via mesenteric lymph nodes to the thoracic duct and return to gut via the bloodstream.
What do gut-homing effector T cells bind to on endothelium?
MAdCAM-1.
How are T cells moved from the endothelium to the epithelium of the gut?
Through the chemokines that gut epithelial cells express specific for gut-homing T cells.
What allows lymphocytes primed in the gut to migrate to other mucosal sites?
MAdCAM is also found in the vasculature of other mucosal sites.
What is an example of the common mucosal immune system involving mothers and children?
There is passive immunity transfer in breast milk as the T cells for the gut pathogen encountered will be present in the mucosa of the breast tissue.
What is a downside to the common mucosal immune system?
It makes vaccine development difficult for some reason.
What is the predominant Ig in the gut?
IgA (then IgM then IgG).
What is the difference between IgA in the gut and in the systemic immune response?
IgA in gut is dimeric, in systemic immune response is monomeric.
What does IgA bind to that allows it to be endocytosed through the epithelial cells into the lumen of the gut?
Poly-Ig receptor.
What happens to the poly-Ig receptor as the IgA transfers to the gut lumen?
Enzymes cleave it to form a secretory components on the IgA which protects the connected bit of both IgA molecules.
What are the 3 ways that IgA helps mucosal immunity?
- Secreted IgA on the gut surface can bind and neutralise pathogens and toxins.
- IgA is able to bind and neutralise antigens internalised in endothelial cells.
- IgA can export toxins and pathogens from the lamina propria while being secreted.
