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Bioregulatory Systems: Upper GI Tract > Gut Immunology (Complete) > Flashcards

Gut Immunology (Complete) Flashcards

1
Q

How large is the surface area of the GI tract and what consequence does this play in relation to antigens?

A

Surace area is 200m2

Therefore has a massive antigen load (exposed to a large amount of antigens)

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2
Q

List 3 examples of things that contribute to the antigen load of the GI tract

A

Resident microbiota bacteria

Dietary antigens

Pathogen antigens

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3
Q

The GI tract is in a state of restrained activation. Explain what this means and how the GI tract achieves this.

A

GI tract plays a dual immunological role and has to balance between tolerance and active immune response

Example of tolerance includes: Food antigens and Commensal bacteria

Active immune response: Immunoreactivity to pathogens

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4
Q

Give 2 examples of tolerance displayed in the GI tract

A

Tolerance to food antigens

Tolerance to commensal bacteria

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5
Q

Immune homeostasis of gut & development of healthy immune system requires on what important factor?

A

Presence of bacterial microbiota

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6
Q

The gut bacteria is considered a ‘virtual organ’ due to the fact that?

A

1014 gut bacteria versus 1013 cells in body

Provide traits we have not had to evolve on our own - Genes in gut flora 100 times our own genome.

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7
Q

What are the main types of organisms that contribute to the gut microbiota?

A

Viruses

Fungi

Bacteria (Bacteroidetes, Firmicutes, Actinobacteria, Proteobacteria),

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8
Q

List the 4 main phyla of bacteria that are present in the gut microbiota

A

Bacteroidetes

Firmicutes

Actinobacteria

Proteobacteria

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9
Q

Which region of the GI tracts contain the highest and lowest bacterial content?

A

Highest: Colon

Lowest: Stomach

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10
Q

List 2 host factors that can increases bacteria cell numbers and 2 factors that can decrease cell numbers and explain why it affects numbers.

A

Increase: Ingested nutrients and Secreted nutrients (Promotes bacterial growth)

Decrease: (Lead to cell lysis and bacterial elimination)

Chemical digestive factors (Lysis)

Peristalsis contractions (Eliminiation)

Defecation (Elimination)

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11
Q

Suggest a reason why the colon has the highest bacterial cell numbers in the GI tract.

A

Due to lack of secretion of chemical digestive factors in this region versus various other GI tract regions.

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12
Q

List 3 examples of chemical factors released from the stomach which can influence bacterial cell numbers

A

HCL

Pepsin

Gastric lipase

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13
Q

List an example of a chemical factor released from the liver which can influence bacterial cell numbers in the duodenum.

A

Bile acid

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14
Q

List an example of a chemical factor released from the small intestine which can influence bacterial cell numbers

A

Brush border enzymes

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15
Q

List 3 examples of chemical factors released from the pancreas which can influence bacterial cell numbers in the jejunum

A

Tripsin

Amylase

Carboxypeptidase

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16
Q

Define symbiont

A

Organism that lives with the host and neither benefit or harm the other

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17
Q

Define commensal bacteria

A

Bacteria that benefits from the host but does not help or harm the host

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18
Q

Define pathobiont

A

An initially non-harming symbiont that becomes pahogenic under certain (usually enviornmental) conditions

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19
Q

Define dysbiosis

A

Altered microbiota composition

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20
Q

List 5 factors that can influence dysbiosis

A

Infection or inflammation

Diet

Xenobiotics (chemical foreign to the body or substances e.g. drugs)

Hygeine

Genetics

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21
Q

Dysbiosis can have multiple effects on the body due to?

A

Production of harmful bacterial toxins and metabolites

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22
Q

Dysbiosis can have multiple effects on the body. List 3 examples of effects it can have on the brain

A

Stress

Autism

Multiple sclerosis

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23
Q

Dysbiosis can have multiple effects on the body. Give an example of its effects on the lung?

A

Asthma

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24
Q

Dysbiosis can have multiple effects on the body. Give 2 examples of a consequence of its effects on the Liver.

A

Nonalcoholic fatty liver disease (NAFLD) [Range of liver diseases that occur in people who dont drink]

Non-alcoholic steatohepatitis (NASH) [type of NAFLD caused by buildup of fat leading to hepatitis]

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25
Q

Dysbiosis can have multiple effects on the body. Give 2 examples of a consequence of its effects on the adipsoe tissue

A

Obesity

Metabolic diseases

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26
Q

Dysbiosis can have multiple effects on the body. Give 2 examples of a consequence of its effects on the intestine.

A

IBD (inflammatory bowel disease)

Coeliac disease

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27
Q

Dysbiosis can have multiple effects on the body. Give 2 examples of systemic consequences.

A

T1DM

Atherosclerosis

Rheumatoid arthiritis

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28
Q

What is the first, second and last line of mucosal defense in the GI tract?

A

1st line: Physical barrier

2nd line: Commensal bacteria

3rd line: immunological response

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29
Q

Mucosal defense involves which two types of physical barriers? Give 2 examples for each type of physical barrier

A

Anatomical physical barriers (e.g. epthielial barriers and peristalsis)

Chemical physical barriers (e.g. enzymes and pH)

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30
Q

In which three ways does the epithelial barrier provide protection in the GI tract?

A

Mucus layer (produced by goblet cells)

Epithelial monolayer (has tight junctions)

Paneth Cells of small intestine (Secrete antimicrobial peptides (defensins) & lysozyme)

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31
Q

Where are paneth cells located and how do they provide protection within the GI tract?

A

Located in the small intestine within the bases of crypts of Lieberkühn.

Secrete antimicrobial peptides (called defensins) and lysozymes

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32
Q

Which two types of tissues provide immunological mucosal defense within the GI tract?

A

MALT: Mucosal associated lymphoid tissue

GALT: Gut Associated Lymphoid Tissue

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33
Q

Where is MALT located?

A

Found in the submucosa below the epithelium, as lymphoid mass containing lymphoid follicles.

The oral cavity is rich in immunological tissue.

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34
Q

Where is MALT located and briefly describe its structure which enables it to perform its imunological functions

A

Found in the submucosa below the epithelium, as lymphoid mass containing lymphoid follicles

Follicles are surrounded by HEV postcapillary venules, allowing easy passage of lymphocytes

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35
Q

Name the venules which sorround the lymphoid follicles of MALT.

A

HEV (high endothelial venule) postcapillary venules

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36
Q

Give 3 examples of regions of the oral cavity which contains high amount of lymphoid tissue (MALT)

A

Paletine tonsil

Lingual tonsil

Pharyngeal tonsil

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37
Q

GALT is responsible for which types of immunological responses?

A

Both active and innate immunological responses

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38
Q

List 6 cellular components which make up the GALT.

A

B lymphocytes

T lymphocytes

Macrophages

APC (dendritic cells)

Epithelial lymphocytes

Intra-epithelial lymphocytes

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39
Q

What is the role GALT plays in the active and innate immunological response? (2)

A

Producing lymphoid cells and antibodies

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40
Q

GALT can be considered as non-organised and organised. What are 2 examples of non-organised GALT?

A

Intra-epithelial lymphocytes (e.g. T-cells, NK cells) [Makes up 1/5th of intestinal epithelium)

Lamina propria lymphocytes

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41
Q

GALT can be considered as non-organised and organised. What are 4 examples of organised GALT?

A

Peyer’s patches (small intestine)

Caecal patches (large intestine)

Isolated lymphoid follicles

Mesenteric lymph nodes (encapsulated)

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42
Q

Diagram showing differences between large and small intestine

A
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43
Q

Where are Peyer’s patches located?

A

Found in submucosa small intestine (mainly distal ileum)

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44
Q

Briefly describe the structure of Peyer’s patches

A

Aggregated lymphoid follicles covered with follicle associated epithelium (FAE).

Contains an organised collection of naïve T cells, B-cells and a subethilial dome containing dendritic cells

45
Q

How does follicle associated epithelium (FAE) differ from normal epithelium of the intestinal tract? (3)

A

No goblet cells

No secretory IgA

No microvilli

46
Q

The development of naive T-cells and B-cells of the Peyer’s patches requires exposure to?

A

Requires exposure to bacterial microbiota

47
Q

How does the amount of Peyer’s patches differ between the last trimester of pregnancy up until teenage years?

A

50 in last trimester foetus, 250 by teens

48
Q

What component of the FAE (Follicle associated epithelial cells) plays a role in antigen uptake and transfer to Peyer’s patches?

A

Microfold cells (AKA M cells)

49
Q
A
50
Q

Briefly describe the role of M cells

A

M cells play a role in antigen uptake for peyer’s patches

M cells express IgA receptors, facilitating transfer of IgA-bacteria complex into the Peyer’s patches

51
Q

What 2 cells of the GI tract play an important role in antigen sampling?

A

Microfold cells (M cells)

Dendritic cells

52
Q

Briefly explain how dendritic cells play a role in antigen sampling

A

Dendritic proccesses can pass through the tight junction of the epithilial cells, enabling them to sample antigens present within the lumen.

They the trnasfer the anrtigens sampled and deliver them to mesenteric lymph nodes

53
Q

Explain how the B-cell adaptive response occurs within the Peyer’s patches.

A

Mature naïve B-cells express IgM in Peyer’s Patches

On antigen presentation class switches to IgA

T-cells & epithelial cells influence B cell maturation via cytokine production

B cells further mature to become IgA secreting plasma cells and populate lamina propria

54
Q

Mature niave B-cells express which type of antibodies in peyer’s patches? How does this change when presented with an antigen?

A

Mature naïve B-cells express IgM in Peyer’s Patches

On antigen presentation class switches to IgA

55
Q

T-cells & epithelial cells influence B cell maturation via?

A

Cytokine production

56
Q

Up to 90% of gut B-cells produces which type of antibody?

A

IgA

57
Q

Explain how secretory IgA is secreted into the gut lumen.

A

Activated plasma cells produce and secrete dimeric IgA in the submucosa

IgA binds to poly-ig receptors and is taken into the epithelial cells.

Enzymatic cleavage between the IgA and receptor occurs and secretory IgA is released into the lumen to perform its function

58
Q

Explain the role of secretory IgA in the gut lumen

A

sIgA binds luminal antigen preventing its adhesion and consequent invasion.

59
Q

Briefly explain what occurs during lymphocytic homing and circulation

A

Antigens from gut lumen taken in and presented to Peyer’s patches for antigen presentation and activation.

Activated lymphocytes then travel to mesenteric lymph nodes where lymphocyte proliferation occurs.

Lymphocytes then return to the circulation via thoracic duct.

Once it enters circulation it can travel to the peripheral immune system (e.g. skin, tonsils BALT [Bronchus-associated lymphoid tissue])

An alternative route would involve exiting the peripheral immune system and entering the intestinal mucosa via vessels in the lamia propria

60
Q

Enterocytes & goblet cells of small bowel have a short life span (about 36 hrs) versus other types of epithelial cells. Suggest 3 reasons why rapid turnover of enterocytes occurs.

A

Enterocytes are first line of defense against GI pathogens & may be directly affected by toxic substances in diet.

Effects of agents which interfere with cell function, metabolic rate etc will be diminished.

Any lesions will be short-lived.

61
Q

What is a consequence of impairment of rapid turnover of enterocytes?

A

Severe intestinal dysfunction will occur

62
Q

Give an example of a cause of rapid enterocyte cell turnover dysfunction

A

Radiation

63
Q

Cholera is a acute bacterial disease caused by which bacteria and its serotypes?

A

Vibrio cholerae serogroups O1 & O139

64
Q

Explain how vibrio cholerae leads to development of cholera

A

Bacteria reaches small intestine → contact with epithelium & releases cholera enterotoxin.

Once inside the epithelial cells, it activated adenylate cyclase activity, increasing cAMP levels.

This results in increased secretion of Na+, K+, Cl- and HCO3-, leading to osmotic movement of water into the lumen of the intestinewhich results in presentation of diarrhea

65
Q

Cholera infection is transmitted via which route and how does it spread?

A

Transmitted via Faecal-oral route

Spreads via contaminated water & food.

66
Q

What are the two main symptoms of cholera?

List 3 other common symptoms of cholera

A

Severe dehydration

Watery diarrhoea

Vomiting

Nausea

Abdominal pain.

67
Q

What is the gold-standard diagnostic investigation for a patient suspected of having cholera?

What is an alternative investigation that can be used?

A

Gold standard: bacterial culture from stool sample on selective agar

Rapid dipstick tests also available

68
Q

What is the main treatment option for a patient with cholera?

A

oral-rehydration is the main management (up to 80% of cases can be successfully treated)

69
Q

What is a medical preventative measure against cholera infections?

A

Vaccine: Dukoral (oral inactivated vaccine)

70
Q

How common are cholera cases globally versus in the UK?

A

Globally 1.3 - 4 million cases, avg. 95,000 deaths/year

Uk around 2017 - 13 cases (with last indigenous case being in 1893) [Check travel history]

71
Q

Define gastroenteritis

A

Inflammation of the stomach and intestines, typically resulting from bacterial toxins or viral infection and causing vomiting and diarrhoea (aka stomach bug)

72
Q

List 2 viral causes of infectious diarrhoea (gastroenteritis)

A

Rotavirus (Children)

Norovirus (Winter vomitting bug)

73
Q

Which gastroenteritis causing virus is most common in children?

A

Rotavirus

74
Q

The ‘winter vomitting bug’ is caused by which type of virus?

A

Norovirus

75
Q

List 2 parasitic causes of infectious diarrhoea (gastroenteritis)

A

Giardia lamblia

Entamoeba histolytica

76
Q

List 6 bacterial causes of infectious diarrhoea (gastroenteritis)

A

Vibrio cholerae

Campylobacter jejuni

Escherichia coli

Salmonella

Shigella

Clostridium difficile

77
Q

What type of virus is the rotavirus and where does it replicate?

A

RNA virus

Replicates in enterocytes

78
Q

What are the 5 types of rotaviruses and which one is most common in human infections?

A

Type A-E

Rotavirus type A most common in human infections

79
Q

What pathogen is the most common cause of diarrhoea in children and infants worldwide?

A

Rotavirus

80
Q

What is the main treatment option for gastroentertisis in children caused by rotavirus?

A

Oral rehydration therapy

81
Q

Before the vaccine was introduced, most individuals had a rotavirus infection by which age? What was the consequence of this?

A

Individuals had an infection by age 5, repeated infections develop immunity.

82
Q

Name the vaccine introduced in the UK to fight against rotavirus type A. What type of vaccine is it?

A

Rotarix (Live attenuated oral vaccine)

83
Q

What type of virus are noroviruses and what is their incubation period?

A

RNA Virus

24-48 hour incubation period (until symptoms appear)

84
Q

How does norovirus transmit itself? How long can a person be contagous and what communites tend to be affected by the virus?

A

Faeco-oral route transmission

Can shed the virus for up to 2 weeks

Outbreaks often occur in closed communities (e.g. on cruise ships

85
Q

What is the main symptom of noroviruses and how long would a person usually be symptomatic for?

A

Acute gastroenteritis

Symptomatic for 1-3 days

86
Q

What species of norovirus is the most common cause of acute gastroenteriris symptoms?

A

Norwalk virus

87
Q

What is the main diagnostic investigation for norovirus and what is the treatment option

A

Sample PCR

Ussually no treatment option required

88
Q

How many cases of norovirus occur each year?

A

685 million per year

89
Q

What are the two most common species of campylobacter?

A

Campylobacter jejuni

Campylobacter coli

90
Q

What are the 3 most common ways campylobacter is transmitted?

A

Undercooked meat (especially poultry)

Untreated water

Unpasteurised milk

91
Q

Suggest a reason why campylobacter can easily cause illness after infection.

A

Low infective dose, a few bacteria (<500) can cause illness

92
Q

What is the main treatment option for a patient infected with campylobacter.

A

Treatment not usually required (unless extremely unwell)

If so Azithromycin (macrolide) is the standard antibiotic

93
Q

What is the most commonest cause of food poisoning in the UK?

A

Campylobacter

94
Q

How many cases of campylobacter infections in the UK per year?

A

Estimated 280,000 cases per year in UK, 65,000 confirmed

95
Q

Name the diverse group of Gram-negative intestinal bacteria present in humans.

A

Escherichia coli (E. coli)

96
Q

E. coli is a diverse group of gram-negative bacteria in the GI tract and are mostly harmless. How many of these types of E coli are pathogenic and are associated with diarrhoea (diarrhoeagenic)?

A

6 pathotypes of E.coli considered diarrhoeagenic

97
Q

Is E.coli gram positive or gram negative?

A

Gram negative

98
Q

Name the 6 pathogenic types of E.coli

A

Enterotoxigenic E. coli (ETEC)

Enteroinvasive E. coli (EIEC)

Enterohaemorrhagic or Shiga toxin-producing E. coli (EHEC/STEC)

Enteropathogenic E. coli (EPEC)

Enteroaggregative E. coli (EAEC)

Diffusely adherent E. coli (DAEC)

99
Q

Name the type of E.coli responsible for causing watery diarrhoea and briefly describe how it causes this.

A

Enterotoxigenic E. coli (ETEC)

Produces a cholera-like toxin

100
Q

Name the type of E.coli responsible for causing bloody diarrhoea which is typical of a shigella like illness.

A

Enteroinvasive E. coli (EIEC)

101
Q

Which type of E.coli is considered to cause the most serious medical complications and why?

A

Enterohaemorrhagic or Shiga toxin-producing E. coli (EHEC/STEC)

Produces a shigatoxin/verotoxin which can result in development of haemolytic uraemic syndrome (loss of kidney function) in around 5-10% of cases.

102
Q

What is haemolytic uraemic syndrome?

A

condition that can occur when the small blood vessels in your kidneys become damaged and inflamed, resulting in blood clots that can lead to kindey failure

103
Q

Name a type of bacteria that is known to be particularly problematic in hospital settings due to being highly contagious

A

Clostridium difficile (C. diff)

104
Q

Explain why clostridium difficile tends to emerge in hospital settings.

A

C.diff exists normally in the gut and does not cause problems when a patient is in a normal healthy state.

If a patient is being treated with therapeutics (e.g. antibiots, probitoics, faecal microbiotic transplantations (FMT), this places their gut in a intermediate dysbiotic state due to reducing numbers of distubrance-sesnitive commensal bacteria.

This has a chance of progressing into a diseased state in which the environment is supportive for C. diff to thrive.

105
Q

What is the step by step management plan for a patient who has a C.diff infection?

A

Isolate the patient

Stop current antibiotics

Give Metronidazole or Vancomycin

May consider Faecal Microbiota Transplantation (FMT) (98% cure rate)

106
Q

What is the reccurence rate of a patient with C.diff becoming reinfected after intial infection and what is the consequence of this?

A

Recurrence rate 15-35% after initial infection, increasingly difficult to treat.

107
Q

What treatment option has been show to be particularly effective in treating C.diff infections?

A

Faecal Microbiota Transplantation (FMT) – 98% cure rate

108
Q
A

Bioregulatory Systems: Upper GI Tract (13 decks)

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