Manifestation of Novel Social Challenges of the European Unionin the Teaching Material ofMedical Biotechnology Master’s Programmesat the University of Pécs and at the University of DebrecenIdentification number: TÁMOP-4.1.2-08/1/A-2009-0011

SIGNALING IN THE INNATE IMMUNE SYSTEM PRR SIGNALING

Tímea Berki and Ferenc BoldizsárSignal transduction

Manifestation of Novel Social Challenges of the European Unionin the Teaching Material ofMedical Biotechnology Master’s Programmesat the University of Pécs and at the University of DebrecenIdentification number: TÁMOP-4.1.2-08/1/A-2009-0011

TÁMOP-4.1.2-08/1/A-2009-0011

PAMPsThe microbe-specific molecules that are recognized by a given Pattern Recognition Receptor (PRR) are called Pathogen-Associated Molecular Patterns (PAMPs):• Bacterial carbohydrates (e.g. lipopolysaccharide or

LPS mannose)• Nucleic acids (e.g. bacterial or viral DNA or RNA),• Bacterial peptides (flagellin, ax21)• Peptidoglycans• Lipotechoic acids (from Gram positive bacteria)• N-formylmethionine, lipoproteins and fungal glucans• Endogenous stress signals are called DAMPs (danger-

associated molecular patterns) and include uric acid

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Endocytic Pattern-Recognition Receptors • Mannose receptors of phagocytes are C-type lectins

bind mannose-rich glycans with mannose or fructose as the terminal sugar that are commonly found in microbial glycoproteins and glycolipids.

• Scavenger receptors bind to bacterial cell wall components such as LPS, peptidoglyan and teichoic acids and stressed, infected, or injured cells. Scavenger receptors include CD36, CD68, and SRB-1.

• Opsonin receptors bind microbes to phagocytes.• N-formyl Met receptors bind N-formyl methionine,

the first amino acid produced in bacterial proteins.

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Signaling Pattern-Recognition Receptors • Cell surface /Extracellular TLRs: TLR1, TLR2, TLR4,

TLR5, and TLR6 • Signaling PRRs found in the membranes of the

endosomes /phagolysosomes: TLR3, TLR7, TLR8, and TLR9

• Signaling PRRs found in the cytoplasm: NOD1, and 2 (CARD-containing proteins)

TÁMOP-4.1.2-08/1/A-2009-0011Signaling PRRs found in the membranes of the endosomes/phagolysosomes• TLR-3, 7 and 8 bind single- or double-stranded viral

RNA • TLR-9 binds unmethylated cytosine-guanine

dinucleotide sequences (CpG DNA)• Most of the TLRs that bind to viral components

trigger the synthesis of interferons that block viral replication within infected host cells

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Toll-like receptors (TLRs)• They are single, membrane-spanning, non-catalytic

receptors that recognize structurally conserved molecules derived from microbes

• They receive their name from their similarity to the protein coded by the Toll gene identified in Drosophila in 1985 by Christiane Nüsslein-Volhard. The gene in question, when mutated, makes the Drosophila flies look unusual, or 'weird'. The researchers were so surprised that they spontaneously shouted out in German "Das ist ja toll!" which translates as "That´s wild!"

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Toll-like receptors-pattern recognition

Peptidoglycan (G+)Lipoprotein

Lipoarabinomannan (Mycobacteria)LPS (Leptospira)

LPS (Porphyromonas)GPI (Trypanosoma cruzi)

Yymosan (Yeast) dsRNA FlagellinUnmethylated

CpG DNA

TLR2TLR1 TLR5TLR3 TLR9TLR6TLR2

Lipoteichoic acids (G+)RVS F protein

LPS (G-)

TLR4CD14 MD-2

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The horseshoe structure of TLR3

TLR3 structure showing attached sugars (spheres) and internal structures (wires, arrows, and helixes)

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MyD88 TRIF

TLR3TLR7

TLR2

PKA TAK1 PKR

p38 JNK

MKKs lkBp50

p65

MyD88

LPS

TLR4

MyD88

MD2LBP

dsRNA

TBK1IKKe

MDA-5RIG-1

IPS1

TLR9JAK2

mTOR

PI3K

CD14

TLR types

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TLR signalingInduces potent innate immune responses that signal through adaptor molecules:• Myeloid differentiation factor 88 (MyD88)• Toll/interleukin (IL)-1 receptor (TIR) domain

containing adaptor protein (TIRAP)• TIR domain containing adaptor inducing interferon

(IFN) (TRIF)• TRIF-related adaptor molecule (TRAM) to activate

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TLR signaling

TAB2

TLR4

MD2

LBP

TRAF6TRIF TBK1

IRAK1

IRAK4RIP

PI3K

Akt ERK1/2

MEK1/2

p38

MKK3/6

MAP3Ks

JNK

MKK4/7

AP-1

TAK1TRAP TRAM

IRF3

IRF3

IKKs

IkB

NFkB

NFkB

MyD88

IKKe

CD14

Nucleus

Cytoplasm

Plasma membrane

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TLR related transcription factors• Nuclear factor (NFkB) • Activator protein 1 (AP-1)• Interferon regulatory factors (IRFs) to induce antibacterial and antiviral responses

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Toll-like receptor inhibitors

MyD88 TRIF

TLR3TLR7

TLR2

PKA

SP600125SB203580

U0126

PD98059

H-89

Celastrol

Bay11-7082

2-Aminopurine

PepinhTRIFPepinhMYD

TAK1 PKR

p38 JNK

MKKs lkBp50

p65

MyD88

Polymixin B

CLI095

LPS

TLR4

MyD88

MD2LBP

dsRNA

BX795TBK1IKKe

MDA-5RIG-1

IPS1

TLR9

Chloroquine

JAK2

Wortmannin

Rapamycin

LY294002

AG490

mTOR

PI3K

CD14

OxPAPC

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Inflammatory cytokines • Interleukin-1 (IL-1) • Tumor necrosis factor-alpha (TNF-alpha)• Interleukin-12 (IL-12)• Chemokines such as interleukin-8 (IL-8), MCP-1, and

RANTES

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Opsonins• Acute phase proteins like mannose-binding lectin

(MBL), C-reactive protein (CRP)• C3b C4b complement factors• Surfactant proteins in the alveoli SP-A and SP-D • The antibody molecule IgG can function as an

opsonin

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Secreted PRRs• Complement receptors• Collectins • Pentraxin proteins such as serum amyloid and C-reactive

protein • Lipid transferases • Peptidoglycan recognition proteins (PGRs)• LRR, XA21D• One very important collectin is mannan-binding lectin

(MBL), a major PRR of the innate immune system that binds to a wide range of bacteria, viruses, fungi and protozoa. MBL predominantly recognizes certain sugar groups on the surface of microorganisms but also binds phospholipids, nucleic acids and non-glycosylated proteins.

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Complement receptors

CR1

CR2

CR3

CR4

CR2

CR3

CR4CRIg

SIGNR1

C3aR

C5aR

C1qR

CD46

CD55

CD59

C3aR

C5aR

C1qRP

Antigen recognitionand uptake

Pathogen recognitionand/or clearance

Modulation of TH1/TH2commitment

Antigen recognitionand uptake

Cytokine modulationand APC maturation

CR1 Inhibits cell proliferationExpressed on <15%

UnknownExpressed on <5%

Cytokine modulationExpressed on activation

T-cell traffickingUpregulated by activation

Cytokine modulation

CD46

CD55

CD59

Activation/proliferation, cytokine modulation andlineage commitment

APC T cell

TÁMOP-4.1.2-08/1/A-2009-0011Overview of complement receptor (CR) and Toll-like receptor signaling

TLRCR3 C5aR

C3b

gC1qR

C1q

CD46

iC3b

C5

Bacteria Viruses

Erk1/2 PI3KTLR4-induced IL-12 inhibited

by posttranscriptional mechanism

Nucleus

IL-12p35IL-12/IL-23p40IL-23p19IL-27p28

IRF-1,IRF-8

C5a