Pathophysiology of IBDNew Developments

Lloyd Mayer, MDMount Sinai Medical Center

New York, NY

Pathophysiology of IBDNew Developments

• Genetic factors in IBD• Environmental factors in IBD• Immunological factors in IBD

Immune response in the normal intestineDysregulated immune response in CDDysregulated immune response in UC

• Targets for biologics in IBD

Genetic Factors in IBD

• Monozygotic twin concordance rates40% to 60% for CD 5% to 20% for UC

• 15-fold increased risk if first-degree relative has IBD

• Conserved pattern of disease in CD• Genome-wide screens have identified

7 loci with linkage to IBD (IBD1-7)• NOD2 (CD), OCTN1/2 (CD), IL23R

(UC and CD)Ahmad T et al. Gastroenterology. 2004;126:1533.

Halfvarson J et al. Gastroenterology. 2003;124:1767.Peeters M et al. Gastroenterology. 1996;111:597.

Science 2006;314:1461-3.

Environmental Factors in IBD• Many distinct environmental triggers -

“barrier breakers”Cessation of cigarette smoking (UC)Bacterial and viral infectionsDrugs: NSAIDs, antibiotics

• Bacteria clearly play a role in IBDGut flora indispensable to development of animal models of IBDTreatment with metronidazole effective in fistulizing CD Patients with IBD fail to show tolerance to their own floraNo evidence that a specific infection (eg, Mycobacterium paratuberculosis) leads to the diseaseDietary contents may influence the type and function of the flora (e.g. aluminum, iron)

Blichfeldt P et al. Scand J Gastroenterol. 1978;13:123.Campieri M et al. Gut. 2001;48:132.Duchmann R, et al. Clin Exp Immunol. 1995;102:448-455. Oliva-Hemker M et al. Inflamm Bowel Dis. 2002;8:112.

Podolsky DK. Acta Gastroenterol Belg. 1997;60:163.Pullan RD et al. N Engl J Med. 1994;330:811.

Sandborn WJ et al. Ann Intern Med. 1997;126:364.Tannock G. Inflamm Bowel Dis. 2003;9:S12.

No immune activation

No immune No immune activationactivation

Macrophage and TH1immune

activation

Macrophage Macrophage and THand TH11immune immune

activationactivation

No colitisNo colitis ColitisColitis

Resident bacteriaResident bacteriaResident bacteriaNo bacteriaNo bacteriaNo bacteria

Role of Commensal Enteric Bacteria in the Pathogenesis of Role of Commensal Enteric Bacteria in the Pathogenesis of Chronic Intestinal InflammationChronic Intestinal Inflammation

MiceIL-2KO (↓)

IL-10KO

TCRα KO

CD3Ε26TGMDR1KO

SAMP1/Yit (↓)CD45RBhi SCID

RatsHLA-B27 TG

IndomethacinGuinea pigsCarrageenan

Non-human primateCotton top tamarin

Are there specific bacteria involved in IBD pathogenesis?

• 16S rDNA studies suggest restricted bacterial repertoire in IBD patients (~500 species in normals)

• Cbir reactive T cells can transfer IBD in mouse models

• The same bacterial species can function differently in distinct environments (? role of aluminum, iron, trace elements) - may explain differences in disease onset and severity in different institutions.

“Bacterially”-Generated Phenotypes

Kim et al. Gastro. 128:891-906, 2005

IL-10-/- Commensal Bacteria Colitis

Germ FreeIL-10-/- No Colitis

E. FecalisIL-10-/- Left sidedColitis

E. coliIL-10-/- Right sidedColitis

Immunological Factors in IBD: The Normal Intestine

Geared towards a non-response (tolerance) to dietary antigens and commensal flora

Innate ImmunityHard-wiredImmediate

Cell bound receptorsPattern-molecular

recognitionMacrophages,

NK cells, non-prof APC

Adaptive ImmunityRequires priming

Delayedor immediate

Soluble and cellular

Antigen-specific

B & T-cells

Rethinking the mechanismsin IBD pathogenesis

Innate ImmunityInitiation

AugmentationEffector cells

Adaptive ImmunityPerpetuation

Augmentation

Regulation

Rethinking the mechanismsin IBD pathogenesis

Tight Junctions Regulate Epithelial Permeability

BARRIERTIGHT JUNCTION

OCCLUDINCLAUDIN

CADHERINJAM-ZO1

The permeability of tight junctions is controlled by changes in gene expression and phosphorylation of junction proteins.

TOXIC AGENTS

LUMINAL BACTERIA

Hydrophobic Mucus Protects the Epithelial Cell Layer

Mucin oligosaccharides bind with ITF to form a hydrophobic lining on the luminal surface.

TOXIC AGENTSMUCINSMUC2, 3

GOBLETCELL

INTESTINAL TREFOIL FACTOR (ITF)

MECHANICAL INJURY

Innate Immunity: NOD2 Signaling Activates Proinflammatory Cytokines

↑NF-κB

NOD2 SENSES PEPTIDOGLYCANS (MDP)

PROINFLAMMATORY RESPONSEINTRACELLULAR

BACTERIA

PanethPanethCellsCells

AntigensAntigens

NOD2NOD2

PanethPanethCellsCells

NOD2 ExpressionNOD2 ExpressionIncreased with Increased with

inflammatory mediatorsinflammatory mediators

BacteriaBacteria

Normal villi/ low NOD2

Kobayashi, KS et al. Science (2005)307:731

NOD2 Contributes toNormal Mucosal Defenses

Innate Immunity: Antimicrobial Defensins

Defensins are cationic antimicrobial peptides that can be activated constitutively or in response to bacterial components.

CONSTITUTIVEDEFENSINS

HBD-1

INDUCIBLEDEFENSINSHBD-2, 3, 4

St

Adaptive Immunity: Hyporesponsive Antigen-Presenting Cells and Lymphocytes

DENDRITIC CELLS↓ TOLL-LIKE RECEPTORS

MACROPHAGES ↓ TOLL-LIKE RECEPTORS

LYMPHOCYTES DIFFICULT TO

ACTIVATE; UNDERGO APOPTOSIS AFTER

ACTIVATION

Adaptive Immunity: Dampened Lymphocyte Response

PLASMA CELLS

JsIgATGFβ

IL10 IMMUNE EXCLUSION

BLOOD VESSELS

MAdCAM-1

α4β7INTEGRIN

LYMPHOCYTES

J

Immunological Factors in IBD: Crohn’s Disease

Dysregulated Immune Response in CD(Defects in innate and adaptive immunity

and barrier function)

IL-12

IFN-γ TNFMMPsIL-1IL-6PGE2LTO3

-

collagenaseelastase

BACTERIA AND BACTERIAL PRODUCTS

IgG

↓ NOD2

IL23/IL6/TGFβ

IL17

Th17

2 pathways (IL12 and IL23) can mediate inflammation

Is it really a classic Th1 response?IL-23 - a pro-inflammatory cytokineIs it really a classic Th1 response?IL-23 - a pro-inflammatory cytokine

TpTp

Th1Th1 Th2Th2

Effector T Cells

+ AntigenIL-12(p40/P35)

IL-4

IFNγTNF-α

IL-4IL-5IL-10IL-13

Th17

IL-23 (p40/p19)

IL-17

CD4+CD25-

macrophage

IL-1IL-6TNF

IL-12 family of cytokines

p35 -/-Immunogen and

adjuvant

NormalSeverely inflamed

organs

1 week 1 week

p35 deficient mice develop severe arthritis/colitis/encephalopathyp19 and p40-/- mice are spared

p19 or p40 -/-

IL12 and IL23 deficient IL12 deficient only

Dysregulated Immune Response in CDAugmentation (in white) and perpetuation (in yellow)

INFLAMMATIONFIBROSISGRANULOMAS

↑ MAdCAM-1

TNFMMPsIL-1IL-6PGE2LTO3

-

collagenaseelastase

↑ CHEMOKINESCXCL10, 9, 11CCL3

↑LYMPHOCYTE RECRUITMENTCOUPLED WITH

DEFECTS IN APOPTOSIS OF

LPLs

Lack of normal Treg number and function (not FoxP3+ Tregs)

Immunological Factors in IBD: Ulcerative Colitis

Dysregulated Immune Response in UC

CRYPTITIS

C'C'

COMPLEMENT ACTIVATION

IMMUNE COMPLEX

T CELLSNK T CELLS

IFN-γ

IgG

CHEMOKINES:CXCL10CXCL9

CXCL11CCL3

PMN RECRUITMENT

MAST CELL DEGRANULATION

IL-13

Dysregulated Immune Response in UCAugmentation (in white) and perpetuation (in yellow)

T CELLSNK T CELLS

IL-13

IFN-γ

ULCER

MMPsIL-1IL-6PGE2LTTNF O3

-

collagenaseelastase

IL-13↑LYMPHOCYTE RECRUITMENTCOUPLED WITH

DEFECTS IN APOPTOSIS OF

LPLs

Lack of normal Treg number and function (not FoxP3+ Tregs)

Are there defects in Treg cells in IBD?

Normal Intestine Versus IBD Intestine

IBD - Immunoregulation Transfer to immunodeficient

mice

Transfer to immunodeficient

mice

ColitisColitis

ProtectionProtection

ColitisColitis

CD45RBhi

CD45RBhi

CD45RBhiCD45RBhi

CD4+CD25+CD4+CD25+

CD4+CD25+ IL-10-/-CD4+CD25+ IL-10-/-

Powrie et al JEM 1993

CD4+CD25+ T cells

CD45RBlo

Are there defects in CD4+CD25+ T cells in IBD?

• Normal to increased numbers and function of CD4+CD25+ FoxP3+ T cells in IBD mucosa

• Children with genetic deficiency of FoxP3 (IPEX) develop polyautoimmunity and occasionally autoimmune enteropathy but not colitis or ileitis

• CD8+CD28- CD101+ CD103+Vβ5.1+ - TrE cells activated by epithelial cells by antigen (? bacterial lipids) presented by CD1d/gp180 complex

• TrE cells absent in IBD mucosa (Allez, Brimnes, Dotan)

Regulatory T cellsCD8+ T cells

4.72±1.41%2.23±1.04% **In vivo (LPL)% VB5.1 / CD8+ LPL

4.36±2.42%1.52±1.33% *In vitro (IEC:PB T co-culture)%VB5.1 / IEC activated CD8+ T cells (CFSElo)

Normal (n=8)IBD (n=5)

Expansion of CD8+ VB5.1+ T lymphocytes in co-cultures with IECs and normal LPL

p=0.02

p=0.0018

% VB5.1 / CD8+ PBL- 0.3-0.8%

Model of IBD pathogenesis

Environment

Genetics

Mucosal Inflammation

Antigen:•Appropriate•Inappropriate•Modified

Modifiers:•Smoking•Appendectomy•? Diet •Failure of normal

immunoregulation•Over/persistentstimulation•Recruitment ofunregulatable cells

•Permeability•Immunoregulation•Immune response•Colonization

Alteredbacteria

Dietmetals