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MIIM30003 - Medical & Applied Immunology > Lecture 25 - Evolutionary Immunology - Innate > Flashcards

Lecture 25 - Evolutionary Immunology - Innate Flashcards

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USMLE® Step 1 flashcards
1
Q

Compare the organisms in which innate and adaptive immunity are found

A

Innate:

  • Lower and higher organisms
  • Lower: invertebrates
  • Higher: vertebrates

Adaptive:

  • Higher organisms (only)
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2
Q

When did adaptive immunity first appear?

In which organisms did it appear?

A
  • ~450 million years ago
  • Appeared in agnathans (hagfish, lampreys)
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3
Q

Describe immunity in drosophila

A
  1. Production of anti-microbial peptides
  • Epidermis
  • Fat body / lymph
  1. Phagocytosis
  • Haemocytes
    • Phagocytose and destroy
    • Coagulate surrounding haemolymph
  1. Proteolytic cascades
  • Blood coagulation
  • Complement like components
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4
Q

Phylogenetically, what are the oldest mediators of innate immunity?

A

Phagocytes

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5
Q

Describe the function of haemocytes in Drosophila melanogaster

A
  1. Phagocytosis
    • ROS
    • Oxidants
    • NO
    • Lysozyme
    • Protease
    • Acidification
  2. Proteolytic cascade
    • Release of C’-like components
    • Results in blood coagulation and killing of pathogens
  3. Release of inflammatory mediators
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6
Q

Describe proteolytic cascades

A

eg Complement

  • Many enzymes present in serum (10% of globulin fraction)
  • Zymogens

Activation:

  • Trigger provided by the pathogen
  • Proteolysis of the proteins
  • Products of proteolysis are involved in the desruction of the pathogen

Effects:

  • Lysis of microbe
  • Opsonisation of microbe
  • Inflammation
  • Recruitment of inflammatory cells
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7
Q

Describe the alternative pathway in C’ activation

A
  1. C3 ‘tickover’ in steady state
  2. C3b binds pathogen when present
    1. Thioester group on C3b binds pathogen surface
  3. Factor B binds C3b and is cleaved into Bb and Ba by Factor D
  4. Bb joins with C3b on pathogen surface to form the C3 convertase
  5. Cleavage of C3
  6. etc
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8
Q

Describe activation of the lectin pathway

A
  1. MBL binds mannans on pathogen surface
  2. Activation of MASPs associated with MBL
  3. C4 binds pathogen surface covalently
  4. MASPs convert C4 → C4a & C4b
  5. C4b binds C2
  6. C2 → C2a & C2b by MASPs
  7. C2a joins with C4b
  8. C4bC2a is C3 convertase
  9. C3 → C3a & C3b
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9
Q

Describe the evolutionary homologues of the C’ cascade

A
  1. Activation

Alternate pathway

  • Echinoderms (sea urchins)
  • Homologues:
    • C3 ⇔ SpC3
    • Factor B ⇔ SpBf
    • Factor D homologue?

Lectin pathway

  • Urochordate (sea squirts)
  • Homologues
    • MBL ⇔ Ficolin
  1. Effector function
  • Deposition of C3b on the pathogen surface
  • Opsonisation by coelomocytes
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10
Q

Describe evolutionary homologues of anti-microbial peptides

A

Small cationic molecules

  • eg Defensins
    • Phylogenetically conserved:
      • Humans
      • Plants
      • D. melanogaster

Features

  • Over 400 identified
  • Some show microbe specificity

Structure

  • α-helix and β-sheet
  • This structure is conserved through from plants to humans

Function:

  • Permeabilise pathogen membrane
  • Results in lysis of the pathogen cell
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11
Q

Compare the location of release of defensins in humans and D. melanogaster

A

Humans

  • α-defensins: paneth cells
  • β-defensins: epithelial cells in skin

D. melanogaster

  • Fat body cells (liver equivalent) → systemic response
  • Epithelial cells → local response
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12
Q

Briefly describe defensins in D. melanogaster

A
  • *Drosophila *make many different defensins
  • Expression is induced by Toll signalling following PAMP recognition
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13
Q

What happens to Drosophila if Toll receptors are knocked out?

A

Susceptible to fungal infections

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14
Q

Describe the structure of TLRs

A

LRR: leucine rich repeats

  • 25 aa long

TIR

  • Toll/IL-1R domain
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15
Q

What is the function of TLRs?

A

Recognise PAMPS

Examples:

  • TLR3 - dsRNA
  • TLR4 - LPS
  • TLR5 - Flagellin
  • TLR9 - CpG DNA
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16
Q

List some other types of PRRs

A
  • TLRs
  • NLRs (NOD-like receptors)
  • RLRs (RIG-like receptors)
  • CLR (C-type lectin like receptors)
17
Q

In which organisms did innate immunity arise?

A

Metazoans

eg Cnidarians, arthropods etc.

18
Q

Describe the components of the innate immune system in the following:

  • Protozoa
  • Sponges
  • Worms
A

All have phagocytic cells

Worms also have NK cells

19
Q

Describe the emergence of LNs

A

Seen in mammals (+/- birds)

Not found in sharks or fish

20
Q

Describe the evolution of Ig

A

Increasing n° of classes seen as we move up the phylogentic tree

21
Q

What type of organism are the following:

  • D. melanogaster
  • C. elegans
  • Sea urchins
A
  • D. melanogaster - Arthropod
  • C. elegans - Nematode
  • Sea urchins - Echinoderm
22
Q

What is the basis of TLR diversity in humans?

A

Variation in LRR sequences

23
Q

Compare the location of the various PRRs in humans

A

Cell surface

  • TLR4 ⇔ LPS
  • TLR5 ⇔ Flagellin
  • TLR6-TLR2 ⇔ Peptidoglycan etc.
  • TLR1-TLR2 ⇔ Peptidoglycan etc.

Endosomes

  • TLR3 ⇔ dsRNA
  • TLR7 ⇔ ssRNA
  • TLR9 ⇔ CpG DNA

Cytosol

  • RIG-I ⇔ dsRNA
  • NOD-1 ⇔ Degraded Gram -ve peptidoglycan
  • NOD-2 ⇔ Muramyl dipeptide
24
Q

Describe signalling through TLRs in mammals and Drosophila

What is evolutionarily interesting about this?

A

The sigalling cascades are conserved through from Drosophila to mammals

Mammalian

  1. PAMP ligates TLR
  2. MyD88 recruitment to TIR domain of TLR
  3. IRAK1 and IRAK4 recruitment to Death domain of MyD88
  4. IRAK1/4 are kinases, and result in a phosphorylation cascade
  5. TRAF6
  6. TAK1
  7. Degradation of IKK
  8. Release of NFKB
  9. NFKB drives transcription of pro-inflammatory cytokines and co-stimulatory molecules

Drosophila

  1. Gram +ve bacteria
    • Peptidoglycan binds PGRP-SA and GNBP-1
    • These activate Grass
  2. Fungi
    • PR1 released by fungi
    • This activates Persephone
  3. *Persephone *and Grass cleave and activate Späztle
  4. Späzle dimerises Toll receptors on cell surface
  5. dMyd88 is recruited to TIR domains
  6. Recruitment of Pelle and Tube to dMyD88
  7. Phorphorylation cascade?
    • dTRAF?
    • Cactus kinase?
  8. Phosphorylation and degradation of Cactus by Pelle (equivalent of IκB)
  9. Release of DIF (equivalent of NFKB)
  10. DIF activates gene transcription
    • Drosomycin
    • Immune response proteins
25
Q

Describe TNF signalling in mammals and Drosophila

What are the potential outcomes of this signalling?

A

The pathways are shared in these organisms

Mammals

  1. TNF binds TNFR1
  2. Recruitment of RIP
  3. Recruitment of TRAF2 to RIP
  4. TRAF triggers a phosphorylation cascade
  5. Activation of IKK (IκB kinase complex)
  6. Phosphorylation and degradation of IκB
  7. Release of NFκB
  8. Activation of transcription
    • Pro-inflammatory cytokines
    • Co-stimulatory molecules

Drosophila

  1. PGN products from Gram -ve bacteria activate PGRP-LC receptor on surface
  2. Recruitment of Imd
  3. Recruitment of dFADD
  4. dFADD triggers phosphorylation cascade
    • dTAK1
  5. Phosphorylation and degradation of C-terminal of Relish (equivalent of IκB)
  6. Cleaved Relish moves into nucleus and activates gene transcription
    • Diptericin

Triggering of apoptosis

Mammals

  1. Receptor recruits FADD
  2. Activaiton of caspase-8
  3. Apoptosis

Drosophila

  1. PGN products from Gram -ve bacteria activate PGRP-LC on cell surface
  2. Recruitment of Imd
  3. Recruitment dFADD
  4. Recruitment of Dredd (Caspase-8 equivalent)
  5. Apoptosis
26
Q

Describe expanision of innate immunity in echinoderms

A

Huge expansion of SRCR (Scavenger receptors)

  • 1000 compared to human 81

Protects them from the many viruses that it experiences every day

Though sea urchins lack adaptive immunity, they are working with what they do have

27
Q

Explain the funciton of the following molecules

  • PGRP-SA
  • TRAF
  • DIF
  • Cactus
  • IKK
  • Grass
  • Pelle
  • GNBP-1
  • IRAK1/4
  • Persephone
  • MyD88
  • Spätzle
  • NFκB
A

PGRP-SA

  • Proteoglycan recognition protein SA
  • Binds peptidoglycan of Gram +ve bacteria

TRAF

  • Part of phosphorylation cascade after TLR activation in mammals

DIF

  • Drosophila equivalent of NFKB
  • Turns on transcription of immune response proteins

Cactus

  • Drosophila equivalent of IKK

IKK

  • IκB kinase
  • Phosphorylates the inhibitory component of NFκB, causing its degradation
  • NFκB is free to translocate into the nucleus

Grass

  • Serine protease
  • Activated by GNBP and PGRP that have recognised peptidoglycan extracellularly
  • Activates Späztle complex

Pelle

  • *Drosophila *equivalent of IRAK1/4
  • Serine kinase
  • Phosphorylates cactus (IκB equivalent), resulting in its degradation and release of DIF (NFκB equivalent)

GNBP-1

  • Gram -ve binding protein
  • Binds peptidoglycan of Gram +ve bacteria

IRAK1/4

  • Serine/threonine kinases
  • Recruited to death domain of MyD88
  • Trigger a phosphorylation cascade, resulting in activation of IKK → release of active NFκB

Persephone

  • Serine protease
  • Directly activated by PR1, a virulence factor from fungi
  • Acts on Späztle complex

MyD88

  • Adaptor protein
  • Recruited to (intracellular) TIR domain of activated TLR
  • Recruits IRAK1/4 to death domain

Späztle

  • Cleaved by activated *Grass *and Persephone
  • Once cleaved, acts on Toll receptor

NFκB

  • Transcription factor
  • Turns on transcription of pro-inflammatory cytokines, co-stimulatory molecules
28
Q

Describe the domains of MyD88 and why these are important

A
  • Domain that binds intracellular TIR domain of TLR
  • Death domain
    • Recruits IRAK1/4
29
Q

Describe the role of the following molecules:

  • Imd
  • FADD
  • Caspase-8
  • dFADD
  • TRAF
  • RIP
  • PGRP-LC
  • Dredd
A

Imd

  • ‘Immune deficiency’
  • Adaptor protein for PGRP-LC

FADD

  • Adaptor protein recruited to TNFRI
  • Leads to apoptosis through recruitment of Caspase-8

Caspase-8

  • Recruited by FADD
  • Leads to formation of apoptosome

dFADD

  • Drosophila equivalent of FADD
  • Recruits Dredd

TRAF2

  • Recruited to TNFRI
  • Triggers phosphorylation cascade, leading to degradation of IκB and release of NFκB

RIP

  • Recruited to TNFRI
  • Recruits TRAF2

PGRP-LC

  • Peptidoglycan recognition protein LC
  • Recognises peptidoglycan products from Gram -ve bacteria

Dredd

  • Drosophila equivalent of Caspase-8
  • Recruited by dFADD
30
Q

Compare detection of Gram +ve and -ve bacteria by Drosophila

A

Gram +ve:

  • Detected by PGRP-SA
  • Activates Toll pathway

Gram -ve:

  • Detected by PGRP-LC
  • Activates Imd pathway
31
Q

Compare the effects of recognition of Gram positive and negative bacteria in Drosophila

A

Gram positive:

  • Activation of Toll pathway
  • Transcription of Drosomycin

Gram negative

  • Activation of Imd pathway
  • Transcription of Diptericin or apoptosis
32
Q

Compare the expression of the following:

  • Diptericin
  • Drosomycin
A

Diptericin: Gram -ve bacteria

Drosomycin: Gram +ve bacteria & fungi

33
Q

Where are defensins produced in Drosophila?

A
  • Fat body cells (liver equivalent) → systemic response
  • Epithelial cells → local response
34
Q

Compare recognition of pathogens in mammals and Drosophila

A

Humans:

  • Many receptors that are capable of recognising specific pathogen markers
  • Receptors are at the cell surface, cytosol, or endosome

Drosophila

  • Much of the recognition occurs extracellularly
  • Pathogen detection proteins:
    • ​PGRP-SA
    • GNBP1
  • The binding of these proteins to pathogen products brings about cleavage and activation of proteases, which cleave and activate Spätzle.
  • Spätzle can then activate Toll, triggering the signalling cascade
35
Q

Describe, in detail, how Gram +ve bacteria and Fungi activate Toll receptors

A

Gram +ve bacteria:

  • Peptidoglycan binds PGRP-SA and GNBP1
  • This complex activates Grass
  • Grass cleaves and activates Späztle into a dimer

Fungi:

  • Fungal cell wall components bind PR1
  • This complex activates Persephone
  • Persephone cleaves and activates Späztle into a dimer

Spätzle dimerises Toll receptors on the surface of the cell, triggering a signalling pathway

36
Q

What are **PGRP-SA, GNBP1, **and PGRP-LC?

A

Pathogen detection proteins:

  • PGRP-SA
  • GNBP1
  • Recognise peptidoglycan from Gram +ve bacteria extracellularly
  • This complex is now capable of cleaving and activating Grass

PGRP-LC:

  • Binds Gram -ve peptidoglycan products
  • Triggers the Imd pathway
37
Q

How are Fungi recognised by Drosophila?

A
  • Fungal cell wall components bind PR-1
  • This complex then activates Persephone
  • etc. (Toll pathway)

MIIM30003 - Medical & Applied Immunology (30 decks)

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