Anatomy and Homeostasis
of the GI Tract
Dr Joanne Pennock
Infection, Immunity and Respiratory Medicine
Overview: The GI Tract is essentially a mucosal surface designed to protect us from potential infection whilst allowing absorption of essential nutrients
How does our GI tract keep us healthy?
Jejunum Colon
Overview: The GI Tract has an undulating surface which increases surface area for absorption and secretion
CRYPT VILLUS
SUBMUCOSA & MUSCLE
Stomach
Stomach:
Lumen pH 1-2
H+ Pepsin
HCO3-
Mucus pH 7
Pre-epithelial
Protection of gastric epithelium by mucus and secretion of neutralising bicarbonate by specialised epithelial cells
pH gradient
Stomach: The case for H pylori
1982: Lancet Robin Warren and
Barry Marshall published a study
with 100 patients showing that H
pylori strongly associated with
gastric and (later) duodenal ulcers.
In 1988 published showing that
in 92% of patients where H pylori
had been cleared with
antibiotics, their ulcer had
healed.
Gastric/duodenal ulcers caused by: NSAIDS (20%) H pylori (80%)
Figure 1 Demonstration of Helicobacter pylori by the four
staining methods: (A) modified Giemsa, (B) anti-H pylori
antibody immunostain, (C) modified McMullen's method,
(D) H pylori silver staining (HpSS) method.
Rotimi et al. J Clin Pathol 2000;53:756-759
Stomach: The case for H pylori
Stomach: The case for H pylori
Atuma C et al. Am J Physiol Gastrointest Liver Physiol 2001;280:G922-G929
The GI tract is lined with a variable layer of mucus
• Lubricant
• Prevents mechanical stress
on epithelium
• Thick layer provides stable
microenvironment
• Prevents invasion
• Essential environment for
microflora
Johansson M E V et al. PNAS 2008;105:15064-15069
Mucus is secreted by goblet cells
Mucus in the GI tract:
World's largest E. coli outbreak kills 14 in Germany (May 2011)
3,500 infected 855 developed rare haemolytic uraemic syndrome (HUS) 53 died
Enteroaggregative strain of E. coli had acquired Shiga toxin which caused HUS
Mucus in the GI tract: A layer of mucus is essential to health
Muc5ac: a critical component mediating the rejection of enteric nematodes. Hasnain et al. Exp Med. 2011 May 9;208(5):893-900. Epub 2011 Apr 18.
Mucus in the GI tract: All mucus is not created equal…
Mucus and the microbiome:
Johansson M E V et al. PNAS 2008;105:15064-15069
Upper layer of mucus is colonised by bacteria
Mouth Anus
Mucus and the microbiome:
?
Mucus and the microbiome:
Antimicrobial Peptides: a and b defensins, Reg3a
Antimicrobial Peptides:
Antimicrobial Peptides:
Essential for bacterial
clearance.
Eg Salmonella
typhimurium
• Administration of antibiotics can downregulate
antimicrobial peptides and increase susceptibility to some virulent bacteria
• eg hospital patients became susceptible to ancomycin-
resistant Enterococcus • In mice giving microbial products (LPS) after antibiotics, can
increase resistance and upregulate antimicrobial peptides
Antimicrobial Peptides:
i.e. gut bacteria actually stimulate secretion of antimicrobial peptides maintaining homeostasis
BEVINS C L et al. Gut 1999;45:911-915
Copyright © BMJ Publishing Group Ltd & British Society of Gastroenterology. All rights reserved.
‘’Twenty years ago you wouldn't have expected this, but
there's been a dramatic change in the view of what
microorganisms like bacteria can do to host physiology,"
[Sven Pettersen] said.
The microbiome is essential to health:
The absence of gut bacteria affects:
• Behaviour
• Gut homeostasis
• Immune response under stress
• Body weight
• Brain development and gene expression
Heijz et al PNAS 2011
Why not switch to ‘healthy’ bacteria??
•‘Mutaflor’ •Ulcerative Colitis •Gastroenteritis •IBS •Pouchitis •Crohn’s disease
Each capsule 2.5-25x10(9) viable cells
The microbiome is essential to health:
Faecal transplant therapy
Faecal transplant therapy
A recent systematic review concluded that, although there are a variety of methods used to infuse intestinal microorganisms (as part of a suspension of healthy donor stool) into the intestine of patients in order to restore the microbiota, of 317 patients treated across 27 case series and reports, this approach was highly effective at achieving resolution of recurrent CDI (92% resolved). Adverse events have rarely been reported (Gough et al., 2011). Typically, fresh manipulated faeces (30–50g) from a healthy donor is administered in normal saline by enema, slurries via nasogastric tube, or colonoscopy.
Public Health England 2013
• The leading cause of health care-associated infectious diarrhea (1,646 deaths
in England and Wales 2012)
• Caused by a spore-forming gram positive bacillus which is part of normal
healthy flora in 4% of healthy individuals.
• Spores are resistant to stomach acid
• Once in intestine, germinate and move into vegetative state
Clostridium difficile infection
Asymptomatic Severe diarrhea
Severe abdominal pain
White blood cell count >15000 cells/ul
Toxic megacolon
Organ failure
Mortality rate 35-80%
Clostridium difficile infection
• Virulence is evolving
• Total cases rose dramatically
1999-2005
• Reported infections still on the
rise
• Reported deaths falling
• Considered a new ‘epidemic’??
• Most often found in a health care setting
• Spores are easily spread
• Recent administration of antibiotics is key risk factor
• Change in flora facilitates colonization & proliferation
Clostridium difficile infection
Taken from: Clostridium difficile infection: how to deal with the problem. Department of Health & Health Protection
Agency 94 cases reported in Jan and Feb 2015 in University Hospital of South Manchester alone.
Clostridium difficile infection
van Nood E et al. N Engl J Med 2013;368:407-415.
Rates of Cure without Relapse for Recurrent Clostridium difficile Infection.
Clostridium difficile infection: First randomised clinical trial 2013
The microbiome is essential to health
IgA is a GI specific antibody responsible for primary defence against bacteria
Secretory IgA
http://www.calier.es/
Secretory IgA
•1 in 700 Europeans are IgA deficient •The most common immunodeficiency •Many have no symptoms…. BUT
•IgA deficient patients suffer more episodes of: •bronchitis •pneumonia •chronic diarrhea •conjunctivitis •sinusitis
•1 in 700 Europeans are IgA deficient •The most common immunodeficiency •Many have no symptoms…. BUT
•IgA deficiency often presents with IgG2 deficiency •Increases susceptibility to certain bacteria
The role of secretory antibodies in infection immunity Richard A. Strugnell & Odilia L. C. Wijburg Nature Reviews Microbiology 8, 656-667 (September 2010)
SIgA coats colitogenic bacteria with high affinity:
Palm et al Cell 2014 158: 1000
SIgA coats colitogenic bacteria with high affinity in
Crohn’s and UC patients:
Authors found: • Colitogenic bacteria were highly coated
with IgA
• Antigen specific IgA production
• CD and UC patients each had unique bacterial populations coated with IgA
• When isolated, these bacteria exacerbated colitis in mice
• IgA response is insufficient to clear /neutralize bacteria
• Can IgA coating be used to identify disease-promoting bacteria in individual patients? Palm et al Cell 2014 158: 1000
Natural defences: Mucus, microbiome & antibody BUT the GI tract is also lined with a single layer of epithelial cells which delineate our host tissue from the outside environment
Pre-epithelial
Simple columnar Epithelium
Sub-epithelial
Bacteria Mucus IgA Innate & adaptive cellular responses
Epithelium:
Stomach Jejunum Colon
Epithelium:
Epithelium: Houses key effector cells
Paneth cells
Stem
cells
Proliferative
zone
Differentiation
zone
Epithelium: Cell renewal & differentiation
Need to strike a balance between apoptosis and proliferation
Epithelium: Cell renewal & differentiation
Damage resulting in denuding of epithelium
Restitution Healing Healing completed
• Most common intestinal parasite found in the USA.
• 10-25 cysts can cause clinical disease.
• Pathology results from vilous atrophy and crypt hyperplasia.
• Parasite increases enterocyte apoptosis – ultimately resulting in atrophy,
malabsorption, and weight loss.
Giardia intestinalis
Epithelium: Cell renewal & differentiation
Volta and Villanacci Cellular & Molecular Immunology (2011) 8, 96–102;
Coeliac disease
Pasparakis Nature Reviews Immunology 9, 778-788 (November 2009)
Epithelium: Cell renewal & differentiation
Pre-epithelial
Epithelial
Sub-epithelial
Bacteria Mucus IgA Innate & adaptive cellular responses
Sub-Epithelium:
Sub-Epithelium:
Focus on: Lamina propria Lymphocytes
How does the immune system put a brake on inflammation?
Glocker et al N Engl J Med. 2009 November 19; 361(21): 2033–2045.
A case in point: A deficiency in IL10 receptor
Glocker et al N Engl J Med. 2009 November 19; 361(21): 2033–2045.
A case in point: A deficiency in IL10 receptor
http://arthritis-research.com/content/7/2/62/figure/F1
Why IL10 receptor? Tregs are essential for control
T cell populations contribute to homeostasis
T cell populations contribute to homeostasis
•Ulcerative colitis (UC) •Crohn’s Disease (CD)
Inflammatory Bowel Disease
Crohn’s Disease
Barrier defects: Tight junction dysfunction
Paneth cell defects: Reduced secretion of HD5
Paneth cell defects: NOD2 polymorphisms Potentially affecting microbiome and response to commensal flora
Effector T cell / T reg imbalance
Defective cell migration
Defective neutrophil function
•Ulcerative colitis (UC) •Crohn’s Disease (CD)
Inflammatory Bowel Disease
Dysregulation of host flora may cause disease
Homeostasis is key to regulating inflammation
•Ulcerative colitis (UC) •Crohn’s Disease (CD)
Inflammatory Bowel Disease
• Inflammatory bowel disease (IBD) includes:
– Ulcerative colitis and
– Crohn’s disease
• The overall increased risk of colorectal cancer for someone with IBD is estimated to be 4-20 times higher than normal.
• Personal history of type 2 diabetes
– Increases your risk of having colorectal cancer and colorectal polyps by 50 percent
Having Inflammatory Bowel Disease and Type 2 Diabetes Are Risk Factors for
Colorectal cancer
Having Inflammatory Bowel Disease and Type 2 Diabetes Are Risk Factors for
Colorectal cancer
• Ten patients in each group • Relative abundance of bacterial
phyla shown
Unravelling the effects of the environment and host genotype on the gut microbiome Aymé Spor, Omry Koren & Ruth Ley Nature Reviews Microbiology 9, 279-290 (April 2011)
• In most people, colorectal cancers develop slowly over a period of several years.
– 10 to 20 years
• Chances of developing colorectal cancer sometime in your life:
– A man has a 1 in 17 chance.
– A woman has a 1 in 18 chance.
What is colorectal cancer?
What is colorectal cancer?
• Colorectal cancer usually begins as a non-cancerous (or benign) polyp.
• A polyp
– is a growth inside the colon or rectum that is not normal.
– can be several types.
– is not always cancerous.
What is colorectal cancer?
Inflammatory bowel disease and intestinal cancer: a paradigm of the Yin–Yang interplay between inflammation and cancer S Danese1 and A Mantovani2 Oncogene (2010) 29, 3313–3323
An inflammatory microenvironment promotes tumorigenesis
An inflammatory microenvironment promotes tumorigenesis
NOD2-mediated dysbiosis predisposes mice to transmissible colitis and colorectal cancer Couturier-Maillard et al. J Clin Invest 2013
Microbial Dysbiosis in Colorectal Cancer (CRC) Patients Sobhani et al. PLoS ONE Jan 2011 The Gut Microbiome Modulates Colon Tumorigenesis Zackular et al. Mbio Nov 2013
Figure 1. Bacterial genera abundance differentiates cancer patients and normal colonoscopy
individuals.
Sobhani I, Tap J, Roudot-Thoraval F, Roperch JP, Letulle S, et al. (2011) Microbial Dysbiosis in Colorectal Cancer (CRC) Patients.
PLoS ONE 6(1): e16393. doi:10.1371/journal.pone.0016393
http://journals.plos.org/plosone/article?id=info:doi/10.1371/journal.pone.0016393
Dysbiosis promotes tumorigenesis
Intrinsic pathway to
inflammation (in tumour
cells)
Extrinsic pathway driven by chronic inflammation (eg
IBD, dysbiosis)
Tumour Progression
• Normal tissue homeostasis disrupted • Sequential mutations • Epigenetic alterations • Oxidative stress (Bcl2, p53) • Proliferation / apoptosis dysregulation
• Inflammatory tumour microenvironment • Inflammatory cytokines (TNFa, IFNg, IL1, IL6) • Reduced regulatory cytokines (IL10, TGFb) • Disrupted homeostasis • Proliferation / apoptosis disregulation
The Cancer-Inflammation Paradigm
Summary: • Many effectors play a role in gut homeostasis • Epithelial cells play a major role in maintaining a physical
barrier and triggering immune responses • Mucus, the microbiome and regulatory cells together are
essential for gut health • Sub-epithelial immune cells maintain homeostasis and
respond to the gut environment • Sub-epithelial cells are primed to respond to breaches in the
intestinal barrier