LEcture 10: innate immunity

Question 1

What types of PRR (Pattern recognition receptors) are there?

Answer 1

• Membrane bound PRRs, such as:
– Toll-like Receptors (TLR)
– The mannose receptor (MR)
– C-type Lectin receptors

• Cytoplasmic PRRs, such as:
– NOD-like receptors (Nod1/2, Nalp1-13)
– RNA helicases (CARD’s)

• Secreted PRRs, such as:
– Complement receptors
– C-reactive protein
– mannan-binding lectin (MBL)

Question 2

Structure of TLR?

Answer 2

LRR: domain outside the cell (leucine rich repeats)
TIR: inside the cell. Convers signal. Highly conserved for signaling.

Question 3

TLR are expressed on

Answer 3

virtually all immune cells.

Question 4

Processes in TLR signalling?

Answer 4

1. Recognition of the ligand
2. dimerization of receptors
3. Selective recruitment of adaptorproteins
4. Specific activation of kinase pathways
5. Translocation of transcriptionfactors to the nucleus
6. Expression of target gene(s)

Question 5

Two pathways the TLR ( TIR domain ) can induce?

Answer 5

Two pathways:
1) MyD88-dependent: inflammatory cytokines
2) MyD88-independent:
Type 1 interferons

Question 6

TLR recognition of micro-organisms: what is important in recognizing bacteria and what in recognizing viruses?

Answer 6

• Bacteria, fungi, protozoa
– metabolism differs from hu mans
– PAMPs are: Carbohydrates & Lipid structures .
Ligands are very important! recognition by extracellular TLR
• Viruses

– Viruses use host metabolism for replication
• Carbohydrates and lipids are same as host
• Nucleotides (RNA/DNA) are similar to that of the host
Viral PAMPs are nucleic acids that appear in an unusual location in infected host cells. Location is very important!
TLR: intracellular

Question 7

How can the Innate immunity be trained?

Answer 7

• Innate immunity can be trained by repetitive contacts with microbes
  (but also by vaccines)
• Innate immunity is not antigen specific contradictory to adaptive immunity, so training protects against a variety of pathogens
• Innate immune training is independent of T/B lymphocytes

Question 8

 TLR activation shifts metabolism towards aerobic Glycolysis. What happens then for innate immune system?

Answer 8

metabolites from glycolysis: cofactors for epigenetic signatures -> Processes involved in training the innate immunity are predominantly epigenetic signatures.

Question 9

TLR expression is dynamically regulated. What is meant by that?

Answer 9

When triggering of single TLR also functional expression of other TLR’s should be taken into account. they trigger each other.

Question 10

Overview

Answer 10

• TLR’s are important PRR on immune cells and various types of
epithelial cells
• TLR’s are located in the cell membrane or endosome according to their
ligand-specificity
• Outcome of TLR signalling depends on the adaptor proteins that are
recruited
• TLR expression within intestinal epithelial cells (and likely in other
cells) is dynamic and regulated
• TLR play an important role in training of both the innate and adaptive
immune system by supporting metabolic adaptations and epigenetic
modifications.

Question 11

How to escape TLR recognition?

Answer 11

alterations in flagellin.
Bacterial modulation of TLR signaling. (by interfering with ubiquitylation of host protein: inhibiting kinase activation)
Make TLR cross-talk with other immune receptors

Question 12

Why is trained immunity a potential therapeutic target?

Answer 12

Trained immunity affects the outcome of inflammatory diseases and
cancers

Question 13

Example of TLR cross talk with other immune receptors: two pathways of M tuberculosis ?

Answer 13

M tuberculosis -> TLR4+ DC- sign = th1 + th2 cytokines. Less harm to host
or -> TLR4: th1 cytokines. more harm to host.

Question 14

Name two Toll-like Receptors that differ in cellular location and give the biological
rationale for that location (2p + 1p)

Answer 14

Extracellular  TLR 1/2, 4, 5, 2/6 (1 point); Ligands from extacellular bacteria, fungi,
protozoa (1 point)
• Intracellular (phagosome)  TLR 3, 7/8, 9 (1 point): Recognize viruses upon
internalization (1 point)

Question 15

Complete this point for point general overview of processes in TLR signalling: (3p)

1. Recognition of the ligand
4. -
5. -
6. Expression of target genes

Answer 15

2. Dimerization of receptors (0,5 pt)
3. Selective recruitment of adaptor proteins (0,5 pt)
4. Specific activation of kinase pathways (0,5 pt)
5. Translocation of transcription factors to the nucleus (0,5 pt)

Question 16

Describe in detail which of the steps (1-6) in the TLR signalling processes is decisive
for outcome of TLR4 signalling after binding of LPS. Include in your answer the
molecules involved and specify the outcome of the signal. (1p + 3p)

Answer 16

Step 3  selective recruitment of adaptor proteins
(+/-TIRAP)
MyD88-independent
Inflammatory 
cytokines
TRIF (+/- TRAM)
Type 1 interferons 
INF/IFN