GI mucosal immunity
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GI mucosal immunity

GI mucosal immunity

Presented by Wat Mitthamsiri, M.D.

March13, 2014

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    GI mucosal immunity GI mucosal immunity Presentation Transcript

    • Gastrointestinal Tract Mucosal Immunity Wat Mitthamsiri, MD. Allergy and Clinical Immunology Unit Department of Medicine King Chulalongkorn Memorial Hospital
    • Outlines • GI Tract structures and functions • GI immune system • GI immune tissue • Innate immunity in GI tract • Adaptive immunity in GI tract
    • GI tract immunity: Importance • Largest organ exposed to external antigens • Multifunctional: – Mucosal barrier – Absorptive surface – Regulation to balance immune reactions against foreign antigens – Fostering the symbiotic, commensal microbiota – Maintain state of tolerance to benign antigens – Maintain appropriate response to pathogenic insults
    • GI TRACT STRUCTURES AND FUNCTIONS
    • Overview
    • Overview http://cnx.org/content/m46506/latest/2402_Layers_of_the_Gastrointestinal_Tract.jpg
    • Esophagus: Overview http://www.highlands.edu/academics/divisions/scipe/biology/faculty/harnden/2122/images/esophagus.jpg
    • Esophagus: Histology http://faculty.une.edu/com/abell/histo/esophagusw.jpg
    • Esophagus: Histology http://www.lab.anhb.uwa.edu.au/mb140/corepages/oral/images/oes041he.jpg
    • Esophagus: Histology http://www.lab.anhb.uwa.edu.au/mb140/corepages/oral/images/oes041he.jpg • Nonkeratinized squamous epithelium • Protects the body from swallowed materials and acid
    • Esophagus: Histology http://www.lab.anhb.uwa.edu.au/mb140/corepages/oral/images/oes041he.jpg • Submucosal glands • Secrete bicarbonate and mucus
    • Esophagus: Histology http://missinglink.ucsf.edu/lm/ids_101_histo_resource/images/222X10_copy.jpg
    • Esophageal epithelium • Intercellular attachment + control of permeability: – Desmosomes, adherens junctions, and tight junctions • Tight junction proteins: – Claudins, occludins, and junctional adhesion molecules • Adherens junction protein: – E-cadherin MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Esophageal epithelium • Junctional proteins: – Superficial cell layers • Claudins 1 and 4 • Occludin • Zo-1 – Intermediate and suprabasal layers • Claudins 1 and 4 • Occludin MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Esophagus: Histology http://www.dartmouth.edu/~anatomy/Histo/lab_5/GI/DMS127/05.gif
    • Esophagus: Histology http://www.dartmouth.edu/~anatomy/Histo/lab_5/GI/DMS127/05.gif
    • Stomach: Overview http://www.paradoja7.com/wp-content/uploads/2013/12/anatomy-of-the-stomach.jpg
    • Stomach: Cardia http://www.paradoja7.com/wp-content/uploads/2013/12/anatomy-of-the-stomach.jpg • Consists of a narrow strip of cells • Epithelia are primarily composed of mucous cells • Protect the esophagus from gastric acidity
    • Stomach: Corpus http://www.paradoja7.com/wp-content/uploads/2013/12/anatomy-of-the-stomach.jpg • Breakdown of food: • Mechanical = Rugal folds • Biochemical = Acid and pepsin • Layer of secreted molecules: • Mucus, trefoil factors, bicarbonate, acid, defensins, and prostaglandins • Protects epithelial surfaces
    • Stomach: Antrum http://www.paradoja7.com/wp-content/uploads/2013/12/anatomy-of-the-stomach.jpg • Antrum • Reservoir for chyme • releases chyme into the small intestine
    • Stomach: Overview http://media.web.britannica.com/eb-media/15/74315-036-756CBAC8.jpg
    • Stomach: Resident cells http://cnx.org/content/m46517/latest/2415_Histology_of_StomachN.jpg
    • Stomach: Resident cells http://cnx.org/content/m46517/latest/2415_Histology_of_StomachN.jpg
    • Stomach: Resident cells http://cnx.org/content/m46517/latest/2415_Histology_of_StomachN.jpg
    • Small intestine: Overview http://www.mhhe.com/biosci/ap/dynamichuman2/content/gifs/0124.gif
    • Small intestine: Cells http://media-2.web.britannica.com/eb-media/18/74318-004-2CEECF6F.jpg
    • Small intestine: Cells http://medcell.med.yale.edu/systems_cell_biology_old/gi/images/stomach_small_intestine_cartoon.jpg
    • Small intestine: Cells http://medcell.med.yale.edu/systems_cell_biology_old/gi/images/stomach_small_intestine_cartoon.jpg
    • Small intestine: Cells MT Abreu, Nature Reviews Immunology 2010, 131-143
    • Colon: Overview http://www.crcftlauderdale.com/images/anat_colon_1.0.jpg
    • Colon: Overview http://www.as.miami.edu/chemistry/2086/Chap%2024/Chapter%2024-newPART2_files/image019.jpg
    • GI IMMUNE SYSTEM
    • GI immune tissue • Intraepithelial lymphocytes • Dense population of resident immune cells in lamina propria • Organized lymphoid structures – Payer’s patches (PP) – Isolated lymphoid follicles (ILF) – Mesenteric lymph nodes • Further divided into effector and inductive sites MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Inductive sites • Organized lymphoid structures consist of: – Naïve T cells, B cells, and APCs – Draining lymph nodes – Specialized lymphoid structures: • PPs in the small intestine • Similar lymphoid tissues in the rectum • Isolated lymphoid follicles • Cryptopatches • After activation in these organized tissues, Ag-specific T and B cells hone in on effector sites MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Inductive sites: Payer’s patch CN Anderson, Nature Reviews Immunology 2001, 59-67
    • Effector sites: Lamina propria • Phagocytes – Engulf and kill microbes • Cytotoxic T cells – Kill infected cells • B cells – Produce neutralizing antibodies • Helper T cells – Production of cytokines MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Effector sites: Lamina propria CN Anderson, Nature Reviews Immunology 2001, 59-67
    • INNATE IMMUNITY IN GI TRACT
    • Components • Mucosal barriers • Antimicrobial peptides • TLRs and NLRs • Intestinal microbiomes • Immune cells MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Mucosal barriers: Anatomy • Extracellular components of the barrier – Epithelial cell surface – Hydrated gel formed by mucins – Unstirred layer of fluid • Cellular components of the mucosal barrier – Epithelial cell membrane – Paracellular pathway: apical junctional complex • Tight junction • Adherens junction JR Turner, Nature Reviews Immunology 2009, 799-809
    • Mucosal barriers: Anatomy JR Turner, Nature Reviews Immunology 2009, 799-809
    • Mucosal barriers: Anatomy JR Turner, Nature Reviews Immunology 2009, 799-809
    • Mucosal barriers: Anatomy JR Turner, Nature Reviews Immunology 2009, 799-809
    • Mucosal barriers: Anatomy JR Turner, Nature Reviews Immunology 2009, 799-809
    • Mucosal barriers: Anatomy JR Turner, Nature Reviews Immunology 2009, 799-809
    • Transportation across tight juction • At least 2 routes found – Leak pathway • Allows paracellular transport of large solutes • Limited flux of proteins and bacterial lipopolysaccharides • Size of particle exclusion has not been precisely defined, but whole bacteria cannot pass • This pathway does not show charge selectivity • Flux across the leak pathway may be increased by cytokines JR Turner, Nature Reviews Immunology 2009, 799-809
    • Transportation across tight juction • At least 2 routes found – Small pores • Defined by tight junction-associated claudin proteins • Primary determinants of charge selectivity • Pores radius: 4 Å • Expression of specific claudins varies between organs and within different regions of a single organ and can be modified by external stimuli, such as cytokines • Properties may be regulated by physiological or pathophysiological stimuli JR Turner, Nature Reviews Immunology 2009, 799-809
    • Leak pathway regulatory measures • MLCK activation – Clearly important • Myosin ATPase – Its activity is regulated by MLC phosphorylation • Members of the Rho kinase family – Phosphorylate MLC directly – Inhibit MLC phosphatase • AMP-activated protein kinase – Activated during stress – Directly phosphorylate MLC JR Turner, Nature Reviews Immunology 2009, 799-809
    • Effect of cytokines on tight juction • a | Occludin is normally concentrated at the tight junction (arrow) in jejunal villus epithelium. Perijunctional actomyosin ring :red, nuclei: blue • b | Exogenous TNF increases myosin light chain kinase (MLCK) activity, which causes perijunctional myosin II regulatory light chain phosphorylation and triggers occludin (green) endocytosis (arrow). This increases flux across the tight junction leak pathway and enhances paracellular permeability to large solutes JR Turner, Nature Reviews Immunology 2009, 799-809
    • Pore regulatory measures • Via synthesis and trafficking of claudin proteins • Expression of specific claudin proteins changes during: – Development – Differentiation – Disease – Response to stressors — including cytokines • Claudin proteins associated with control of cell and organ growth JR Turner, Nature Reviews Immunology 2009, 799-809
    • Pore regulatory measures • Claudin-1 – Increased expression by intestinal epithelial cells of IBD patients – Enhance neoplastic transformation, tumour growth and metastasis in experimental models • Claudin-2 – Increased expression by intestinal epithelial cells in animal models of colitis and IBD patients – IL-13 and IL-17 (increased in the mucosa of patients with colitis) increase claudin-2 expression in vitro, and reduce barrier function JR Turner, Nature Reviews Immunology 2009, 799-809
    • Effect of cytokines on tight juction • c | Claudin-2 expression (green) is limited to crypt epithelial cells. F-actin: red, and nuclei: blue • d | IL-13 can stimulate claudin-2 expression (green) in surface epithelial cells (arrows). This increases flux across small tight junction pores, enhancing paracellular cation permeability JR Turner, Nature Reviews Immunology 2009, 799-809
    • Barrier defect related diseases JR Turner, Nature Reviews Immunology 2009, 799-809
    • Barrier defect related diseases JR Turner, Nature Reviews Immunology 2009, 799-809
    • Barrier defect alone is not enough • Increased paracellular permeability: – Increase mucosal immune activity – Enhance disease progression and severity – Possible risk factor for development of disease – But not enough to cause the disease! • Restoration of tight junction barrier function may be effective in: – Preventing disease in at-risk individuals – Maintaining remission in IBD patients JR Turner, Nature Reviews Immunology 2009, 799-809
    • Barrier loss & immune regulation • Insufficient to cause disease JR Turner, Nature Reviews Immunology 2009, 799-809 Tight junction barrier dysfunction alone
    • Barrier loss & immune regulation • Insufficient to cause disease JR Turner, Nature Reviews Immunology 2009, 799-809 Endoscopic mucosal resection
    • Barrier loss & immune regulation • Still…insufficient to cause disease JR Turner, Nature Reviews Immunology 2009, 799-809 IBD + Endoscopic mucosal resection
    • Tight junction&immune regulation JR Turner, Nature Reviews Immunology 2009, 799-809
    • Antimicrobial peptides • Esophagus – Mucous layer of mucin-2 and glycoproteins – Trefoil factors (TFFs) • Protease-resistant peptides • Produced by goblet cells • Secreted into the mucous layer • Promote epithelial cell survival and migration • Critical for immune defense and epithelial barrier function MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Antimicrobial peptides • Small intestine – Mucous layer – Secretory immunoglobulin (sIgA) – Antimicrobial peptides – Mucins play an important role in normal intestinal immune regulation MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Antimicrobial peptides • Defensins families – α-defensins: • Human neutrophil peptides (HNP) 1 to 6 • Human α-defensin 5 and 6: From Paneth cell – β-defensins: • Human β-defensins (HBD) – HBD1: Multiple locations – HBD2: Small intestine and stomach – HBD3: Esophagus and oral cavity – HBD4: Gastric antrum MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Antimicrobial peptides • Cathelicidins (Human LL-37) • Cryptidins 1 to 6 • Phospholipase A2: Paneth cell • Lysozyme: Paneth cell • Defensins and cathelicidins have chemotactic properties for neutrophils, dendritic cells, and memory T cells MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • TLRs and NLRs: PRRs • Pattern recognition receptors (PRRs): – Receptor molecules expressed in immune cells – Recognize pathogen-associated molecular patterns (PAMPs) • Lipopolysaccharide • Flagellin • Bacterial DNA and RNA – Have crucial roles in innate immunity and protection against pathogens – Also recognize gut-resident microbiota • Most PRRs fall into 3 families: – Toll-like receptors (TLRs) – NOD-like receptors (NLRs) – Retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) N Kamada, et al., Nature Reviews Immunology 2013, 321-335
    • Roles of TLRs in GI tract • Sensing bacteria by the intestinal epithelium • Sensing intestinal injury • Regulate barrier function MT Abreu, Nature Reviews Immunology 2010, 131-143.
    • Expression of TLRs • Localization of TLRs in GI mucosa – By anatomical location – By cell lineage – Spatial restriction by polarization – Intracellular TLRs: TLR4, found in-vitro • Negative regulations of TLRs in GI mucosa MT Abreu, Nature Reviews Immunology 2010, 131-143.
    • Anatomical location of TLRs MT Abreu, Nature Reviews Immunology 2010, 131-143.
    • Anatomical location of TLRs MT Abreu, Nature Reviews Immunology 2010, 131-143.
    • Polarization of TLRs MT Abreu, Nature Reviews Immunology 2010, 131-143.
    • Negative regulations of TLRs • Toll-interacting protein (ToLLIP) – An intracellular protein that inhibits TLR2 and TLR4 signalling through its effect on IL-1R associated kinases (IRAKs) – Expressed by IECs in vitro, especially following stimulation with LPS or lipotechoic acid – LPS-induced inhibition of TLR activation = LPS tolerance • IECs from IBD patients failed to upregulate Tollip expression – This may contribute to chronic inflammation MT Abreu, Nature Reviews Immunology 2010, 131-143.
    • Negative regulations of TLRs • Single immunoglobulin IL-1R-related molecule (SIGIRR; also known as TIR8) – Negative regulator of IL-1R, IL-33R, TLR4 and TLR9 signaling – Highly expressed by IECs – when deleted, made animals susceptible to intestinal inflammation MT Abreu, Nature Reviews Immunology 2010, 131-143.
    • TLRs and epithelial injuries MT Abreu, Nature Reviews Immunology 2010, 131-143.
    • TLRs and epithelial injuries MT Abreu, Nature Reviews Immunology 2010, 131-143.
    • TLRs and barrier functions MT Abreu, Nature Reviews Immunology 2010, 131-143.
    • NOD like receptors (NLRs) • NOD=nucleotide-binding oligomerization domain-containing protein – NOD1 and NOD2 • Cytosolic proteins • Respond to intracellular fragments of bacterial peptidoglycan -> NF-κB-dependent and MAPK- dependent gene transcription DJ Philpott, et al., Nature Reviews Immunology 2014, 9-23.
    • NOD like receptors (NLRs) • NOD1 detects d-glutamylmeso- diaminopimelic acid (iE-DAP) – Dipeptide found in a peptidoglycan – Primarily found in Gram-neg bacteria but also in select groups of Gram-pos bacteria, including Listeria spp. and Bacillus spp. • NOD2 detects muramyl dipeptide (MDP) – Present in bacterial peptidoglycan DJ Philpott, et al., Nature Reviews Immunology 2014, 9-23.
    • NOD like receptors (NLRs) DJ Philpott, et al., Nature Reviews Immunology 2014, 9-23.
    • NODs expression • NODs are expressed by – Epithelial cells – Stromal cells – Neutrophils – Dendritic cells – Paneth cells MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094. DJ Philpott, et al., Nature Reviews Immunology 2014, 9-23.
    • Roles of NODs • NLRP proteins interact with pyrin- containing proteins – Form inflammasomes – Cleave pro-IL-1β and pro-IL-18 into their mature forms by using the caspase-1 pathway • Activation of the caspase pathway -> pyroptosis • NLRPs recognize both bacterial products (e.g., flagellin, toxins) and crystals (e.g., urea) MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • NOD ligand recognition DJ Philpott, et al., Nature Reviews Immunology 2014, 9-23.
    • NOD ligand recognition DJ Philpott, et al., Nature Reviews Immunology 2014, 9-23.
    • Roles of NODs • NOD signaling in the stromal compartment is required for formation of intestinal lymphoid follicles • Interactions between NODs and the microbiome are also essential • NODs are also required for appropriate microflora control • NOD2 deficiency increases bacterial load and decreases the clearance of bacteria from intestinal crypts MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • NOD signaling • Nucleotide-binding function – NBDs of NOD1 and NOD2 mediate ligand- induced oligomerization and hydrolyse ATP – ATP binding is required for NOD1 and NOD2 activation – ATP hydrolysis is required for deactivation of NOD2 – Mutations that is important for ATP hydrolysis associate with Blau syndrome and early-onset sarcoidosis (caused by auto-activation of NOD2) DJ Philpott, et al., Nature Reviews Immunology 2014, 9-23.
    • NOD signaling • Activation and regulation of RIP2 – Sensing their respective peptidoglycan ligands – NOD1 and NOD2 auto-oligomerization – Activation of RIP2 – Recruitment and activation of the TAK1– TAB2–TAB3 complex – Drives IKK complex activation – IκBα phosphorylation and degradation DJ Philpott, et al., Nature Reviews Immunology 2014, 9-23.
    • Consequences of NODs activation DJ Philpott, et al., Nature Reviews Immunology 2014, 9-23.
    • Consequences of NODs activation • Activation of the MAPKs extracellular signal-regulated kinase 1 (ERK1), ERK2, JUNN-terminal kinase (JNK) and p38 – Lead to expression of pro-inflammatory immune factors • TNF • IL-6, • CC-chemokine ligand 2 (CCL2) • Neutrophil chemoattractants • CXC-chemokine ligand 8 (CXCL8; or IL-8) • CXCL2 • Various antimicrobial factors, including defensins DJ Philpott, et al., Nature Reviews Immunology 2014, 9-23.
    • Consequences of NODs activation • Recruitment and priming innate immune cells • Primes adaptive immune responses and • Key driver of TH2-type immunity • Activation of IFN regulatory factor 7 (IRF7) – > Transcription of type I IFN genes – > Activation of the IFN-stimulated gene factor 3 (ISGF3) complex – > Initiate transcriptional program associated with viral infection DJ Philpott, et al., Nature Reviews Immunology 2014, 9-23.
    • NOD signaling and intestinal berrier • NOD2 has a key role in intestinal homeostasis by – Detecting peptidoglycan released from the gut microbiota – Driving a physiological inflammatory programme through the kinase RIP2, leading to NF-κB activation DJ Philpott, et al., Nature Reviews Immunology 2014, 9-23.
    • NOD signaling and intestinal berrier • In Crohn’s disease – Associated with NOD2 mutations – Some perturbation, which may include antibiotics or an infection, alters the protective inflammatory programme – > breakdown of intestinal barrier – > Maybe dysbiosis • Compensatory immune activation pathways then drives chronic inflammation DJ Philpott, et al., Nature Reviews Immunology 2014, 9-23.
    • NODs and diseases • Loss-of-function mutations of NOD2 – Affecting NOD2-mediated peptidoglycan sensing – Associated with Crohn’s disease • Gain-of-function mutations in the NBD of NOD2 correlate with – Autoinflammatory diseases – Blau syndrome – Early-onset sarcoidosis DJ Philpott, et al., Nature Reviews Immunology 2014, 9-23.
    • NODs and diseases DJ Philpott, et al., Nature Reviews Immunology 2014, 9-23.
    • Intestinal microbiomes • What is “normal gut microbiota”? – Attempts to identify core microbiota – the microbiota that is shared among (most of) humans – have not reached a consensus – 3 types of the microbiota – enterotypes have been proposed – A recent study with largest cohort to date, showed that the concept of enterotypes certainly cannot be applied on the microbiota of infants and young children MR Stojanovic, Best Practice & Research Clinical Gastroenterology 27 (2013) 5–16
    • Intestinal microbiomes • 4 phyla predominate in the human large intestine: – Firmicutes – Bacteroidetes – Actinobacteria – Proteobacteria • These symbionts and the mucosal epithelium have evolved in a mutually beneficial coexistence MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Intestinal microbiomes • It is not clear what represents normal intestinal microbiota • Microbiota composition of healthy subjects differs from that of patients suffering from a number of different diseases • Different microbiota composition related to a disease = dysbiosis MR Stojanovic, Best Practice & Research Clinical Gastroenterology 27 (2013) 5–16
    • Intestinal microbiomes MR Stojanovic, Best Practice & Research Clinical Gastroenterology 27 (2013) 5–16
    • Roles of gut microbiomes • Digest the “resistant carbohydrates” by fermentation – End products of carbohydrate fermentations: • Gas • Short chain fatty acids (SCFAs – acetic, propionic and butyric acid) – SCFAs show anti-inflammatory properties MR Stojanovic, Best Practice & Research Clinical Gastroenterology 27 (2013) 5–16
    • Roles of gut microbiomes • Protein fermentation – Protein degradation mainly occurs in distal colon – Product: Beneficial SCFAs, and also other potentially toxic metabolites – Bacteria are able to produce extracellular proteases – IBD and IBS have been linked to an increased proteolytic activity of intestinal contents – Extracellular microbial proteases are likely to play a role in these diseases’ etiology MR Stojanovic, Best Practice & Research Clinical Gastroenterology 27 (2013) 5–16
    • Roles of gut microbiomes • Deconjugation of bile acids – Primarily performed by intestinal Bacteroides in mouse model – Mechanism for colonic epithelium protection from genotoxic agents – Secondary bile acids had anti-inflammatory effect, (most likely mediated through activation of TGR5 receptor) – Microbiota-mediated metabolism of bile acids is important for the pathogenesis of IBD MR Stojanovic, Best Practice & Research Clinical Gastroenterology 27 (2013) 5–16
    • Roles of gut microbiomes • Mediate gut immune system development N Kamada, et al., Nature Reviews Immunology 2013, 321-335
    • Roles of gut microbiomes • Mediate gut immune system development N Kamada, et al., Nature Reviews Immunology 2013, 321-335
    • Roles of gut microbiomes • Mediate gut immune system development N Kamada, et al., Nature Reviews Immunology 2013, 321-335
    • Roles of gut microbiomes • Help the host fighting pathogens N Kamada, et al., Nature Reviews Immunology 2013, 321-335
    • N Kamada, et al., Nature Reviews Immunology 2013, 321-335
    • N Kamada, et al., Nature Reviews Immunology 2013, 321-335
    • Roles of gut microbiomes • Help the host fighting systemic infection – Role in systemic antibacterial immune responses • Peptidoglycan molecules derived from the microbiota are found in the periphery and can prime peripheral blood neutrophils to facilitate their bactericidal capacity via NOD1 signalling • This enhances host defence against systemic infection with Streptococcus pneumoniae N Kamada, et al., Nature Reviews Immunology 2013, 321-335
    • Roles of gut microbiomes • Help the host fighting systemin infection – Role in systemic antiviral immune responses • Microbiota promotes type I IFN production by macrophages and IFN-priming of NK cells – Role in systemic antiparasitic immune responses • Microbiota induces intestinal TLR-dependent DC activation – Microbiota might provide local tissue-specific defense mechanisms N Kamada, et al., Nature Reviews Immunology 2013, 321-335
    • Roles of gut microbiomes • Roles on IBD – Beneficial subsets of commensal bacteria: Anti-inflammatory activities – Pathobionts are directly suppressed by beneficial commensal bacteria partly through the induction of regulatory immune responses, involving TReg cells, IL-10 and regenerating islet-derived protein 3γ (REGIIIγ) N Kamada, et al., Nature Reviews Immunology 2013, 321-335
    • Roles of gut microbiomes • Roles on IBD N Kamada, et al., Nature Reviews Immunology 2013, 321-335
    • Other roles of microbiomes • Roles on IBD N Kamada, et al., Nature Reviews Immunology 2013, 321-335
    • Immune cells • Eosinophils • Mast cells • Innate lymphoid cells (ILC) • Multifunctional IgA+ plasma cells • Macrophage • Denritic cells MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Eosinophils • Various location distribution – Normal esophageal epithelium: None – Lamina propria (LP) and muscularis mucosa : have eosinophils – Lower GI tract has significant numbers of eosinophils – eosinophil numbers are highest in the cecum and rectosigmoid – Rarely found in the surface and crypt epithelium MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Eosinophils • Intestinal accumulation is independent of bacterial colonization and presence of lymphocytes • Function in nondiseased GI tract: Unknown – Recruited to sites of continual cell turnover ? – Regulate local immunity and tissue repair/remodeling? – Parasite expulsion on chronic or repeat infection can be dysregulated in the absence of eosinophils and IL-5 MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Mast cells • GI: 1 of the largest reservoirs • Esophageal and colonic epithelium is normally entirely devoid of tryptase- positive cells • Tryptase-positive cells are found in varying numbers through the colonic LP • Tryptase-chymase double-positive mast cells predominate in the esophageal LP MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Mast cells • GI mast cells are induced during immune responses to parasites • Their normal function in GI immune homeostasis remains unclear MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Innate lymphoid cells • Members: – Natural killer (NK) – Lymphoid tissue inducer (LTi) cells • Required for lymph node formation during embryogenesis • Produce IL-17 and IL-22 – Natural helper cells – Innate helper type 2 cells – Nuocytes MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Innate lymphoid cells • Relationship between these cell types is currently unclear • Rapid and robust production of Th2 cytokines in response to IL-25 and IL-33 are common • Through production of IL-5, innate lymphoid cells recruit eosinophils and are important for antihelminth immunity MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • IgA+ plasma cells • They have B cell and monocytic and dendritic cell markers. • Some of them produce the TNF-α and inducible nitric oxide synthase – Both of which are required to maintain homeostasis of gut microbiota. • The acquisition of these cells depends on microbial stimulation and gut stroma MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Macrophage • GI mucosa: largest reservoir of mononuclear phagocytes in the body • Intestinal macrophages are derived from circulating monocytes • Resident macrophages are highly phagocytic MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Macrophage • They can ingest microbes and function as scavengers without generating an inflammatory response • Innate signaling molecules such as MyD88 and TRIF adapter proteins are decreased or absent in intestinal macrophages – Which explains the broad TLR nonresponsiveness despite TLR expression MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Macrophage • Functions: – Regulate the inflammatory response to the normal flora – Respond to pathogens – Scavenge debris and dead cells – Phagocytosis and microbial killing MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Denritic cells • Lamina propria contains a dense network of dendritic cells • Functions: – Sample antigen – Initiation of adaptive immune responses • Subset of lamina propria DCs expressing the markers CD11c and CD103 – Express high levels of the flagellin sensor TLR5 – But low levels of TLR4 in comparison to splenic DCs MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Denritic cells activation • Activation through TLR5 leads to: – DC production of IL-23 – ILC expression of IL-17 and IL-22. – These cytokines are important for antimicrobial defense in the intestine • Human intestinal DCs are responsive to TLR3, TLR7, and TLR9 stimulation – May play important role in antiviral immunity MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • ADAPTIVE IMMUNITY IN GI TRACT
    • Components • Antigen uptake • Antigen presentation • Food antigen: Immune tolerance • Microbial antigen: Immune exclusion MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Antigen uptake MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Antigen uptake • Soluble Ag, including many food antigens, are taken up primarily across enterocytes lining the intestinal villus • Under normal conditions, uptake of intact macromolecules occurs by a transcellular transport mechanism for depositing antigenic material across the basolateral surface of the epithelium MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Antigen uptake • When exposed to an Ag, uptake of that Ag can be modified by the presence of Ig – IgA primarily results in immune exclusion – IgG and IgE can enhance uptake through epithelial expression of immunoglobulin receptors (FcRn and CD23, respectively) MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Antigen presentation • Antigen-presenting cells (APCs) in the GI tract – Professional APCs • dendritic cells (DCs) • B cells • Macrophages – Nonprofessional APCs • Epithelial cells. MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Dendritic cells subsets • At oral and esophageal mucosa – Subsets of DCs are distinct from lower GI tract – Greater similarity to DCs in the skin • Langerhans cells • Interstitial DCs • Langerin+ interstitial DCs • Oral DCs acquire and present Ag to T cells – They can generate either tolerance or protective immunity, depending on the context of antigen administration • Whether esophageal DCs can acquire and present ingested food Ag in vivo is unknown MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Dendritic cells subsets • In small and large intestine: 2 DC subsets – CD11b+ CD103− DC • Expresses the chemokine receptor CX3CR1 • Extends dendrites into the small intestinal lumen • Highly phagocytic • Efficiently capture Ag • Not migrate to draining mesenteric lymph node (MLN) • Likely to play a role in recall responses rather than in initiation of immune responses MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Dendritic cells subsets • In small and large intestine: 2 DC subsets – CD11c+ CD103+ DC • Low level of Ag capture • More efficient at Ag presentation • Transport Ag to the MLN for presentation to naïve T cells • Initiation of immune responses to soluble Ag MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Dendritic cells subsets • In the PPs – Subepithelial DCs migrate to T cell areas on appropriate stimulation – Some DC subsets are in the PPs • They can be differentiated by their surface markers, eg. CD11b, CD8α, and CCR6. • There is evidence the different DC phenotypes are specialized to respond to specific inflammatory stimuli or microbial challenges. MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Mononuclear phagocytes • CX3CR1+ phagocytes – No migratory activity – Process and present acquired Ag – Interact with resident T cells of the LP – Participate in the reactivation of memory T cells – Local activation of effector T cells MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Mononuclear phagocytes • CD11c− macrophages of the mouth and small intestines – Present Ag to T cells – Preferentially induce the development of Tregs through an IL-10– and retinoic acid– dependent mechanism. MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Epithelial cells • Capable of presenting Ag to T cells • Induce the expansion of CD8+ T cells with regulatory activity through a CD1d- dependent mechanism • During inflammatory states, epithelial cells of the esophagus and small intestine upregulate MHC II and can activate CD4+ T cells MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Food Ag: Immune tolerance • Intact Ag can be detected in the blood after a meal in healthy volunteers • These Ag were ignored by immune system?:… NO! – Presence of food-specific IgG and IgA antibodies in the serum of healthy individuals • But no immune activation? MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Food Ag: Immune tolerance • Oral tolerance – Oral administration of Ag resulted in the generation of CD4+ and CD8+ T cells with regulatory or suppressive activity • Transfer of CD4+ or CD8+ T cells from fed mice to naïve mice could transfer tolerance in an Ag-specific manner • CD8+ T cells are not required for oral tolerance, but they are capable of mediating tolerance MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Food Ag: Immune tolerance • Deletion of peripherally induced FOXP3+ CD4+ CD25+ Tregs can reverse oral tolerance • DCs migrating from the small intestinal LP are uniquely specialized to program responder T cells to develop into Tregs. MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Oral tolerance MC Berin, et al., Current Biology 23, R389–R400, May 6, 2013
    • Food Ag: Immune tolerance • Liver can also participate in the induction of oral tolerance – Mediated through plasmacytoid DCs – Induce the deletion of Ag-specific CD8+ T cells. • Role of the MLN vs the liver in induction of tolerance may depend on: – Nature of the Ag – How it is handled after breaching the intestinal epithelial barrier MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Food Ag: Immune tolerance • Immune tolerance can be induced through – Airways – Sublingual route • Multiple sites along the GI tract likely contribute to the development of clinical tolerance to food antigens. MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Microbial Ag: Immune exclusion • GI tract: hyporesponsive to signaling through the TLRs • Innate and adaptive immune system work in a coordinated manner to keep the flora compartmentalized to the GI mucosa MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Microbial Ag: Immune exclusion • Absence of signaling through MyD88 and TRIF: – Compensatory systemic Ab response against the intestinal flora – Protects against systemic dissemination of bacteria MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Microbial Ag: Immune exclusion • Commensal bacteria are normally sampled by the mucosal immune system and carried by migratory DCs to the draining MLN – They induce an IgA response partially dependent on T cell help • T cell–independent IgA class switching has also been documented in the intestinal LP. MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Microbial Ag: Immune exclusion • IgA induced by the flora is secreted into the intestinal lumen by epithelial cells expressing the polymeric immunoglobulin receptor (pIgR). • But…IgA deficiency is associated with a relatively mild phenotype. MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Microbial Ag: Immune exclusion • The generation of a commensal flora– triggered IL-17 and IFN-γ response from T cells is associated with pathology in IBD • Conflicting data on the role of the commensal flora in the development of intestinal Tregs MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Microbial Ag: Immune exclusion • In the presence of normal innate and adaptive immune responses within the GI mucosal immune system – Systemic immune system is kept ignorant of the commensal flora – Contrast to the normal immune response to food Ag, in which active immune tolerance is observed systemically MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • Conclusion MC Berin, et al., Gastrointestinal Mucosal Immunology, Middleton’s Allergy 8th edition, 2013, 1084-1094.
    • THANK YOU