Lecture 4- Pattern Recognition Receptors

Question 1

names 2 PAMPS of gram positive bacteria

Answer 1

peptidoglycan
lipoteichoic acid

Question 2

what does PAMP stand for

Answer 2

Pathogen-Associated Molecular Patterns

Question 3

name one PAMP of gram negative bacteria

Answer 3

Lipopolysaccharide (LPS)

Question 4

what are PAMP’s?

Answer 4

microbes contain genetically conserved patterns called PAMPS

• PAMPS are recognized by pattern recognition receptors (PRR) on cells of the innate immune system: macrophages, NK cells, neutrophils, and dendritic cells

Question 5

PRR’s include ____ and a number of ____ to survey all intracellular sites

Answer 5

Toll-like receptors (TLR)
cytosolic receptors

Question 6

name 4 other PRR’s that are involved in enhancing uptake & antigen capture

Answer 6

scavenger receptors
complement receptors
macrophage mannose receptors
C-type lectin receptors

Question 7

name the 2 general types of receptors

Answer 7

uptake & signaling receptors

Question 8

describe uptake receptors and examples

Answer 8

facilitate uptake of particles

complement, scavenger, mannose receptors

Question 9

describe signaling receptors and examples

Answer 9

recognize bacterial PAMP’s and induce activation of the cell through signaling cascades leading to changes in gene expression

Toll-like receptors, NOD-like receptors, RIG-I-like receptors

Question 10

describe structure of Toll-like receptors

Answer 10

• transmembrane molecules (C terminus inside, N terminus outside cell membrane)
• TIR domain can bind to signaling proteins and initiate signaling cascades downstream

Question 11

name 6 TLR’s

Answer 11

TLR2
TLR3
TLR4
TLR5
TLR7/8
TLR9

Question 12

TLR2:

name ligand,
organism expressing ligand
location
the signal adaptor

Answer 12

lipoteichoic acid
gram positive bacteria
plasma membrane
MyD88

TLR2 is a heterodimer with either TLR6 or TLR1- neither have any function by themselves

Question 13

TLR 4:

name ligand
organism expressing ligand
location
the signal adaptor

Answer 13

LPS
gram negative bacteria
plasma membrane
MyD88 (also works with TRIF)

Question 14

TLR 7/8:

name ligand
organism expressing ligand
location
the signal adaptor

Answer 14

viral RNA’s
RNA viruses
endosomes
MyD88

Question 15

TLR 9:

name ligand,
organism expressing ligand
location
the signal adaptor

Answer 15

unmethylated CpG-rich DNA
bacteria
endosomes
MyD88

Question 16

TLR3:

name ligand
organism expressing ligand
location
the signal adaptor

Answer 16

viral RNA
RNA viruses
endosomes
TRIF (for antiviral activation)

Question 17

TLR5:

name ligand
organism expressing ligand
location
the signal adaptor

Answer 17

flagellin (a protein)
bacteria
plasma membrane
MyD88

Question 18

what are the three molecules involved in making LPS accessible to TLR4

Answer 18

LBP
MD2
CD14

Question 19

Why does TLR-4 need help from other molecules to get to LPS?

Answer 19

LPS is a lipophilic (hydrophobic) molecule and needs chaperone proteins

Question 20

how does LBP, MD2, and CD14 help LPS?

Answer 20

• LBP binds to LPS and extracts it from bacterial membrane
• MD2 and CD14 make it possible for TLR-4 to be activated by recognizing LPS

Question 21

describe TLR4 activation signal and its signal cascade

Answer 21

TIR domain of TLR-4 binds to MyD88 (signaling adaptor), this recruits several kinases, there is then a kinase cascade on the cytoplasmic side… result of signaling cascade is activation of transcription factor NFkB, which moves to nucleus and initiates expression of several genes involved in inflammation- synthesis and secretion of TNF-a and other inflammatory cytokines)

Question 22

Know that the difference between TLR signaling through MyD88 vs. TRIF is the end products: TRIF gives a more ___ response and MyD88 gives…

Answer 22

TRIF gives a type I interferon response (interferes with viruses- important in very early stages) while MyD88 yields more pro-inflammatory cytokines like TNF-alpha

Question 23

describe a few cytosolic pattern recognition receptors (PRR)

Answer 23

1. NOD-like receptors – generally recognize bacterial cell wall components
2. inflammasomes – recognize pathogens as well as intracellular damage/injury
3. RIG-I, MDA5 – recognize viral nucleic acids

Question 24

name 5 similarities between cytosolic receptors and TLR signaling

Answer 24

1. ligand binding
2. adaptor molecules facilitate signaling
3. kinase cascade
4. NFkB activation
5. changes in gene expression

Question 25

describe inflammasome signaling

Answer 25

• important for making biologically active IL-1
• first makes pro-IL-1B, cleaved by caspase 1 (activated by inflammasome complex) to make active IL-1B
• NLRP3 (inflammasome) senses change and comes together with adaptor proteins to activate procaspase 1, making active caspase 1 to make IL-1B (most important cytokine- causes fever and triggers inflammation)

Question 26

IL-1 production typically involves activation of ___ and then ___ in order to generate the biologically active cytokine.

Answer 26

TLR
inflammasome

Question 27

Know that activation of inflammasomes is different than TLR in that they can respond to ___, not just ___. Also, know that upon their activation they activate caspases that lead to production of biologically active ___.

Answer 27

cellular damage
PAMPs
IL-1

Question 28

what are the key cytokines of the innate immune response

Answer 28

IL1 / IL6 / TNF-a

Question 29

what do IL1 / IL6/ TNF-a act on?

Answer 29

liver- acute phase proteins (CRP, MBL) —- activation of complement opsonization

bone marrow endothelium- neutrophil mobilization — phagocytosis

hypothalamus & fat, muscle- increased body temp —- decreased viral and bacterial replication