Innate Immunity IV

Describe the structure of TLRs

1. Have leucine rich repeats (LRR) that comprise the horseshoe-shaped extracellular and endosomal binding domain for TLR ligands

2. Has a transmembrane domain (stock domain) that leads to a TIR domain in the cytoplasm

What does the TIR domain do?

Responsible for signalling

What happens when ligands bind to the TLR?

It induces the TLRs to either homodimerize or heteridimerize and initiate signalling

What does the TIR domain interact with? What does this do?

Adaptor proteins that function as sorting receptors for other adaptor molecules and can initiate early polarization of immune response to a pathogen

What are the two locations that TLRs can be?

1. Plasma membrane

2. Endosome/lysosomes

What does TLR4/4 bind to? Where is it found?

Plasma membrane. LPS in gram negative bacteria. Also found in endosomes/lysosomes. Viral proteins

What does TLR2/1 bind to? Where is it found?

PM. Triacly lipopeptides, bacteria, and parasites

What does TLR2/6 bind to? Where is it found?

PM. Diacyl lipopeptides, gram positive bacteria, and fungi

What does TLR5/5 bind to? Where is it found?

PM. Bacterial flagellin

What does TLR11/11 bind to? Where is it found?

PM. Uropathogenic bacteria, toxoplasma profilin

What does TLR12/12 bind to? Where is it found?

PM. Toxoplasma profilin

What does TLR3/3 bind to? Where is it found?

E/L. Viral dsRNA

What does TLR7/7 bind to? Where is it found?

E/L. Viral ssRNA

What does TLR8/8 bind to? Where is it found?

E/L. Viral ssRNA

What does TLR9/9 bind to? Where is it found?

E/L. Bacterial/viral DNA, plasmodium

Generally what do TLRs in the endosome/lysosme bind to? Why?

Nucleic acids and this is because they are not exposed until after they have lost their plasma membrane (happens in the lysosome)

Generally what do TLRs in the plasma membrane bind to?

Structures on the outside of intact microbes

Are most TLRs homodimers or heterodimers?

Homodimers

Describe the TLR4 signalling pathway from the plasma membrane

1. Macrophage will engulf bacterium and release LPS

2. LPS will bind to LBP

3. LBP will pass on LPS to CD14 when it binds to another lysosome or phagosome

4. CD14 will come back to the surface carrying LPS and deliver it to TLR4/4

5. LPS will bind to MD2 (protein on homodimer) on TLR4/4

6. This binding will lead to the activation of the homodimer

7. MyD88 is able to recruit IRAK4 inside the cell

8. IRAK4 will phosphorylate itself

9. IRAK4 will then phosphorylate TRAF6

10. A kinase cascade will occur resulting in IKK to be activated by phosphorylation

11. IKK will bind to NFkB and phosphorylate IkB which leads to the degradation of IkB

12. NFkB is now free and will migrate to the nucleus

13. Binds to the promoter of various genes to produce inflammatory cytokines

What is MyD88?

It is an adaptor protein on the TLR4/4

What is IRAK4?

It is a kinase

What is IKK?

It is an inhibitor of NFkB

What is NF-kB?

It is an active transcription factor that regulates inflammation-promoting genes

What are the five types of inflammation-promoting genes that are regulated by NF-kB?

1. Inflammatory cytokines

2. Chemokines

3. Adhesion molecules on endothelial cells

4. Immune effector molecules

5. Costimulatory molecules

What are 6 types of inflammatory cytokines?

1. TNF-a

2. IL-1

3. IL-6

4. IL-12

5. GM-CSF

6. IFN-a/b

What are four types of chemokine?

1. IL-8

2. MCP

3. RANTES

4. Eotaxin

What are 4 types of adhesion molecules on endothelial cells?

1. ICAM-1

2. VCAM-1

3. E-selectin

4. P-selectin

What are two types of immune effector molecules?

1. Inducible nitric oxide synthetase (iNOS)

2. Defensins

What are two types of costimulatory molecules? What are costiumulatory molecules?

CD40 and CD80/86 on dendritic cells (need a second signal for T cells to be activated)

What does IL-12 do?

It activates NK and T cells

Why are adhesion molecules on endothelial cells important?

This is because they can recruit immune cells that are in the blood to the site of infection

Describe the steps in TLR7 signalling in the endosome

1. Binds ssRNA

2. MyD88 will recruit IRF7

3. TBK1 is recruited and will phosphorylate IRF7

4. IRF7 is active and will go into the nucleus, bind to the promoter and activate IFN-a and IFN-B genes for their production

Describe the steps in TLR3 signalling in the endosome

1. Binds dsRNA

2. TRIF is the adapter protein that will recruit TBK1 and IKK(epsilon)

3. Both kinases will phosphorylate IRF3

4. IRF3 will migrate to the nucleus and bind to the promotor of IFN-B and make this IFN