Immunological Mechanisms and Infections of the GIT Flashcards
State three infections of the GIT.
Oral candidiasis
Helicobacter pylori
Traveller’s Diarrhoea
What does H. pylori cause?
Increased acid secretion
State three causes of Traveller’s Diarrhoea.
Escherichia coli
Salmonella
Shigella
What does Clostridium difficile do?
It takes advantage of antibiotics killing many commensal bacteria - it gains a foothold and then produces toxins to cause mucosal injury.
Treatment may involve FAECAL MICROBIOTA TRANSPLANTATION.
What is the treatment for C. difficile?
Metronidazole and Vancomycin
What components make up mucosal defence?
Anatomical and chemical barriers
Commensal bacteria
GALT and MALT
What makes up the epithelial barrier?
Goblet cells, Paneth cells, antimicrobial peptides, secretory IgA, tight junctions
What is GALT and what does it do?
Collections of T and B cells which generate lymphoid cells and antibodies
Produces secretory and interstitial IgA, IgM, IgG and cell mediated immunity
What do Peyer’s Patches consist of?
Naïve T and B cells
Sub-epithelial dome above the Peyer’s patch which contains dendritic cells
How is the epithelium above Peyer’s patches different to normal gut epithelia?
It is Follicle Associated Epithelium (FAE) - there are no goblet cells, no microvilli and no secretory IgA
In which layer of the gut wall are Peyer’s patches found?
Lamina Propria
Where do activated T and B cells go to proliferate?
Superior Mesenteric Lymph Nodes
What is the role of secretory IgA?
Prevent attachment and entry of pathogens
What immune cell makes up 1/5 of intestinal epithelium?
Intraepithelial lymphocytes
What is the difference between conventional and unconventional T cells?
Conventional - migrate from other tissues
Unconventional - resident, express unusual combinations of CD4, CD8 and gamma delta receptor
What other innate cells are involved?
NK cells
What three signals determine the T cell response?
Presentation of antigen on MHC
Costimulation
Cytokines
What are the mechanisms of immune tolerance?
Anergy
Deletion
Regulation (Tregs)
What is Crohn’s disease?
Inflammatory thickening of the bowel wall - leads to ulceration, diarrhoea and pain
Name 4 structures where GALT is ORGANISED
Caecal patches/Cryptopatches
Peyer’s Patches
Isolated lymphoid follicles
Mesenteric lymphoid follicles
Name 2 places where GALT isn’t organised
Intra-epithelial lymphocytes
Lamina propria lymphocytes
What can happen to healthy microbiota to make it negatively affect the body?
DYSBIOSIS
Gut homing?
Lymphocytes selectively home to sites similar to initial priming.
Antigen presentation in GALT favours gut homing characteristics - specific integrins and chemokine receptors e.g. alpha 4 beta 7 integrin/MAdCAM-1 adhesion
Causes of gastroenteritis/infectious diarrhoea?
Virus = Rotavirus, Norovirus
Bacteria = Campylobacter jejuni, Esterichia coli, Salmonella, Shigella, Clostridium difficile
Protozoal parasitic = Giardia lamblia, Entamoeba histolytica
Coeliac Disease
Autoimmune disease during response to gluten, damage is reversible.
Irritable bowel syndrome
Visceral hypersensitivity which is triggered by diet and stress - it is a function disorder which causes little damage.
Inflammatory bowel disease
Aberrant inflammatory responses to microbiota which can cause serious damage to the GI tract - may require surgery.
2 forms: Ulcerative colitis (restricted to colon, damage to mucosa and submucosa) Crohn's disease (anywhere in GI tract, entire intestinal wall may be affected all the way to the serosa, surgery is not curative)
