GI Mucosal Immunology Flashcards
What does the upper GI tract consist of?
Oesophagus
Stomach
What does the lower GI tract consist of?
Small intestine
Large intestine
In basic terms, what are the 2 kinds of bacteria found in the GI tract?
Commensal bacteria
Pathogenic bacteria
What are some examples of challenges of antigen processing in the GI tract?
Develop self-tolerance
Develop exogenous tolerance
Develop an effective immune response
What is self-tolerance?
Non-responsiveness of the immune system to self-antigens
What is exogenous tolerance?
Non-responsiveness of the immune systemto newly encountered environmental antigens that are harmless
What are examples of different facets to normal antigen processing in the GI tract?
Epithelial layer
Mucus layer
Innate immune response
Antigen presenting cells
Tolerance versus activated of adaptive immune response (T cell)
Soluble mediators of immunity
How does the epithelial layer provide protection?
Specialised tight junctions that regulate permeability
How does the mucus layer provide protection?
Physical barrier keeping microbes from host cells
What are examples of antigen presenting cels?
Dendritic cells
Macrophages
What are examples of soluble mediators of immunity?
Chemokines and cytokines
What are the 2 different parts of the immune system?
Innate immune system
Adaptive immune system
What kind of immune cells are innate?
Granulocyte (neutrophil, eosinophil, basophil)
Mast cell
Monocyte
Dendritic cell
Macrophage
Natural killer cell
What kind of immune cells are adaptive?
CD4+ T cell (memory)
CD8+ T cell (memory)
B cell (memory), which become plasma cells that produce antibodies
Where do all cells of the immune system originate from?
Haematopoitic stem cell which comes from bone marrow
What are the 2 things that a haematopoietic stem cell can differentiate into?
Myeloid progenitor cell
Lymphoid progenitor cell
What does myeloid progenitor cell differentiate into?
RBC
Platelet
All cells of innate immune system (except natural killer cells)
What do lymphoid progenitor cells differentiate into?
All adaptive immune system cells
Natural killer cells
Which immune system causes inflammation?
Innate immune system
What is a key determinant of T cell differentiation?
The cytokine milieu
How do cytokines vary in terms of inflammation?
Some are pro-inflammatory and some are anti-inflammatory
What is a T cell called before it has differentiated into its subtype?
Naive T cell
What are peyer’s patches?
Small masses of lymphatic tissue found throughout the ileum region of the small intestine
What do peyer’s patches allow?
Sufficient sampling of particulate antigens and delivery to antigen presenting cells
What is a macrophage?
Type of phagocyte which is responsible for detecting, engulfing and destroying pathogens and apoptotic cells
What is the first line of defence system in the gut?
Macrophages
What are functions of macrophages?
Sampling of particulate antigens
Phagocytic (ingests harmful pathogens or dying/dead cells)
Secrete cytokines (such as IL-10 required for the survival of FoxP3 and Treg cells)
Antigen presenting cells to modulate adaptive immune response
Where are dendritic cells found in the GI tract?
Lamina propria and peyer’s patches
Why are dendritic cells important for mucosal immune responses?
Efficient sampling of antigen
Different dendritic cell subsets give rise to distinct T cell responses (such as tolerance vs immunity)
Different subsets distinguished by cell markers)
Present antigen to naive T cell
What to dendritic cells do after they have sampled gut bacteria and gut antigens?
Migrate to major lymph nodes
What do dendritic cells undergo maturation into?
Potent antigen presenting cells (APC)
What 3 signals determine T cell response from an antigen presenting cell?
MHC/peptide-TCR
CD80-CD28
Cytokine
Which of MHC/peptide-TCR is on the antigen presenting cell and naive T cell?
MHC on antigen presenting cell
Peptide-TCR on naive T cell
Which of CD80/CD28 is on antigen presenting cell and naive T cell?
CD80 on antigen presenting cell
CD28 on naive T cell
What is the innate immune system based on?
Recognition of pathogens associated molecular patterns (PAMPS/MAMPS)
What T cell is required for clearance of intracellular pathogens?
Th1
What T cell is required for maintaining the immune homeostasis and tolerance?
Treg
What are 2 examples of what happens when the normal immune homeostasis goes wrong?
Inflammatory bowel disease (IBD)
Coeliac disease
What is inflammatory bowel disease?
Chronic, relapsing, remitting inflammation of the GI tract
What are the 2 main examples of IBD?
Crohn’s disease
Ulcerative colitis
What is the difference between Crohn’s disease and ulcerative colitis?
Differ in type and location of inflammation
What does the pathogenesis of IBD involve?
Genome
Microbiome
Environment
Other unknown factors
What is the innate immune systems involvement in IBD?
Dysfunctional innate receptor handling of bacteria
Breakdown of immune tolerance
ILCs
What is the adaptive immune systems involvement in IBD?
Traditionally Th1 versus Th2 paradigm, many other lymphocyte populations are important (such as Th17, regulatory T cells, B cells)
What are different treatment strategies for IBD?
Target lymphocytes directly
Target single cytokines
Target migration of immune cells to GI mucosa
Target multiple cytokines
Target cytokine intracellular signalling pathways
Modulation of microbiota
What does anti-TNF biologics involve?
Inhibition of a single cytokine
What is used to target migration of immune cells to GI mucosa?
Vedolizumab
What are integrins?
Transmembrane proteins used to lymphocyte trafficking and cell adhesion
What drug is used for multi-cytokine blockage?
Ustekinumab
What does multi-cytokine blockage (Ustekinumab) target?
Towards p40 subunit of IL-12 and IL-23
What does IL-12 control?
Proinflammatory Th1 cytotoxic T cell response
What does IL-23 control?
Pro-inflammatory Th17 axis
What drug is used for multi-cytokine blockage through inhibition of intracellular signalling?
Tofacitnib
How does multi-cytokine blockage through inhibition of intracellular signalling with Tofacitnib work?
Pan JAK inhibitor (JAK1 and JAK3)
What interleukins are inhibited by Tofacitnib?
IL2
IL6
IL7
IL9
IL12
IL15
IL21
IL23
IFN
What do initial studies suggest about faecal transmission (FMT) and IBD?
Is likely effective in ulcerative colitis
What is coeliac disease?
Common digestive condition where the small intestine becomes inflamed and unable to absorb nutrients
What does coeliac disease cause intolerance to?
Dietary gluten in wheat and similar proteins
What are symptoms of coeliac disease?
Malabsorption causing failure to thrive as a child
Iron deficiency anaemia
Fatigue
GI symptoms such as loose stool, abdominal pain or asymptomatic
What causes genetic susceptibility to coeliac disease?
HLA-DQ2/8 on antigen presenting cell
What does HLA stand for?
Human leukocyte antigen
What does human leukocyte antigen (HLA) allow?
Immune cells to identify self and non-self antigens
What are consequences of coeliac disease for the gut?
Loss of villi (loss of absorptive capacity)
Increase in intra-epithelial lymphocytes