Mucosal Immunity Flashcards
What are the physiological functions of the mucosal tissue
Gas exchange
Food adsorption
Sensory activities
Reproductions
Do afferent or efferent vessels go into a lymph nide
Afferent
Where are immune responses induced
in organised lymphoid tissues in Peyer’s Patches
Where are immune responses carried out
Scattered lymphoid cells in lamina propria and sub epithelial cells
What are Peyer’s patches covered by
Follicle- associated epithelial layer containing specialized cells called M cells which have characteristic membrane ruffles
What do Peyer’s patches contain
Dendritic cells
Focciles
B cells
T cells
How do M cells take up the antigen
Via antigen sampling
Epithelial cells secrete chemokines which attracts lymphocytes and Dendritic cells (CCR6 and CCR1)
Endocyosis/ Phagocytosis
Tranocytosis
Antigen binds to dendritic cell and activates T cell
How can dendritic cells capture antigen
Extend processes from epithelial layer to lumen of the gut
What cells are found in the epithelial layer
CD8 T cells
What cells are found in the lamina propria
CD4 T ells CD8 T cells Dendritic cells Plasma cells Macrophages
How do T cells enter Peyer’s patches
From blood vessels directed by the homing receptors CCR7 and L selectin
When do T cells in Peyer’s patch become activated
When antigen is transported across M cell and become activated by dendritic cell
How do activated T cells drain
Via mesenteric lymph nodes to the thoracic duct and return to blood stream
What receptors do activated T cells express which home them to the lamina propria and epithelium of the small intestine
CCR9 and a4:b7
What do gut homing receptors bind to
MAdCAM-1
Is MAdCAM specific to the gut
No also found in the vasculature of other mucosal sites
What does breast milk allow
Passive immunity
Proportions of antibodies found in the gut
IgA (80%) - important in preventing infection
IgM (15%)
IgG (5%)
What is unusual about IgA in the gut
It is in its dimeric form
What are the 2 IgA subunits bound by
J chain
What does IgA bind to, to travel through epithelial cell
poly-Ig receptor
What can IgA do
Bind and neutralise pathogens
IgA can bind and neutralise antigen in cell (in endosome)
IgA + Antigen + Secretory compound = export pathogen/ antigen out of lamina propria into lumen
What are the majority of intraepithelial lymphiocyes
90% T cells
90% CD8+
What anchors intraepithelial lymphocytes
ae:B7
What do activated CD8 T cells possess
full killing machinery
What happens when a virus infects mucosal epithelial layer
Infected cell displays viral peptide to CD8 IEL via MHC class 1 Activated IEL kills infected epithelial cell by perforin/ granzyme and Fas dependent pathways
What is the default response of the immune system
Not to react
What is most inhibited in maintaining the balance between protective immunity and homeostasis
Down regulate T cells
What is IBD in simple terms
An inappropriate response to normal mucosa of the gut
In the presence of commensal bacteria production of what inhibits dendritic cell maturation
PGE2
TGF-B
TSLP
What happens when invasive microorganisms penetrate epithelium to activate dendritic cells
Activated dendritic cells express strong co-stimulatory ligands and induce CD4 T cells to differentiate into effector TH1 and TH2 cells
Explain the mechanism of food allergy
Type 1 hypersensitivity reaction initiated by crosslinking of allergen specific IgE on surface of mast cells
What type of reaction is a food alergy
Type 1 hypersensitivity
How is type 1 hypersensitivity reaction initiated
Crosslinking of allergen specific IgE on surface of mast cells - released histamine
What can a food allergy lead to
vomiting
diarrhea
prutusis
urticaria
