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Innate and adaptive immunity. The
mechanisms of innate immunity provide
the initial defense against infections.
Adaptive immune responses develop
later and consist of activation of
lymphocytes. The kinetics of the innate
and adaptive immune responses are
approximations and may vary in different
infections.
Plants or non-vertebrate organisms have molecules and systems that have innate immunity
properties.
Phagocytes
Mammalian Toll like receptors are activated by many different pathogenassociated molecular patterns
TLR 4 recognizes LPS in association with MD2
Intracellular NOD proteins sense the presence of bacteria, recognizing bacterial
peptidoglycans and activating NFkB to induce the expression of pro-inflammatory
genes.
Structural mechanisms of inflammasome assembly
FEBS Journal
Volume 282, Issue 3, pages 435-444, 21 NOV 2014 DOI: 10.1111/febs.13133
http://onlinelibrary.wiley.com/doi/10.1111/febs.13133/full#febs13133-fig-0001
Structural mechanisms of inflammasome assembly
FEBS Journal
Volume 282, Issue 3, pages 435-444, 21 NOV 2014 DOI: 10.1111/febs.13133
http://onlinelibrary.wiley.com/doi/10.1111/febs.13133/full#febs13133-fig-0004
Important “take home” concepts:
1. Cells of the innate immune system like neutrophils, macrophages rapidly eliminate
microbes through phagocytosis.
2. Pattern recognition receptors like TLRs initiate intracllular cascade of signaling that
triggers transcription of proinflammatory mediators.
3. NOD receptors act as intracellular sensors for bacterial infection
4. NALP proteins initiate processing of proinflammatory mediators of the IL-1 family by
activation of inflammasome
NK cells
Activating and inhibitory
receptors of NK cells. A.
Activating receptors of NK cells
recognize ligands on target cells
and activate protein tyrosine
kinase (PTK), whose activity is
inhibited by inhibitory receptors
that recognize class I MHC
molecules and activate protein
tyrosine phosphatase (PTP). NK
cells do not efficiently kill class I
MHC-expressing healthy cells.
B. If a virus infection or other
stress inhibits class I MHC
expression on infected cells, and
induces expression of additional
activating ligands, the NK cell
inhibitory receptor is not
engaged and the activating
receptor functions unopposed to
trigger responses of NK cells,
such as killing of target cells and
cytokine secretion.
Functions of NK cells. A. NK cells recognize ligands on infected cells or cells undergoing other types of stress,
and kill the host cells. In this way, NK cells eliminate reservoirs of infection as well as dysfunctional cells. B. NK
cells respond to IL-12 produced by macrophages and secrete IFN-γ, which activates the macrophages to
kill phagocytosed microbes.
NK cell behavior under homeostatic conditions. Images of NK cells (green) were acquired by twophoton microscopy. As a reference for velocity, images were acquired on LN that had also received
B cells (red). The image sequence was acquired 18 h after NK cell adoptive transfer. (Scale bar: 15
mm.) Time indicated as min/sec. Movie is shown at 15 frames per sec.
NK cells form stable conjugate pairs with allogeneic B cells. The image sequence was acquired 20 h after
NK cell (green) adoptive transfer and shows a single NK-B cell (red) conjugate. (Scale bar: 5 mm.) Time
indicated as min/sec. Movie is shown at 15 frames per sec.
C3 convertase activates C3 for covalent bonding to microbial surfaces by cleaving it into
C3a and C3b and exposing a highly reactive thioester bond in C3b.
Mannan-Binding Lectin
C-type lectin combining a collagen –
like tail with sugar binding domain.
Three gene products combine to
form the basic subunit, which can
form different oligomers
The oligomerization increases the
avidity of MBL – carbohydrate
interaction.
Distinct functions can be
attributed to the different
oligomers
Mannan-Binding Lectin
C-type lectin combining a collagen –
like tail with sugar binding domain.
Three gene products combine to
form the basic subunit, which can
form different oligomers
The oligomerization increases the
avidity of MBL – carbohydrate
interaction.
Distinct functions can be
attributed to the different
oligomers
Why so promiscuous?
Micropattern recognition:
N-acetyl glucosamine, N-acetylmannoseamine, L-fucose and glucose
MBL as an Example for Pattern Recognition
Parasites
•Leishmania
•Trypanosomes
Viruses
•Influenza
•RSV
•HSV
•HIV
Bacteria
•gram negative
•gram positive
•Mycobacteria
•Clamydia
•Yeast/fungi
•Candida
•Aspergillus
MBL Levels in Circulation
MBL plasma
1,000
100
10
1
1000 ng/ml
 40%
100 ng/ml
 10%
MBL Haplotypes
OH
OH
OH
OH
OH OH OH
OH
PGINGFPGKDGRDDTKGEKGEPGQ
OH
PGINGFPGKDGRDGTKGEKGEPGQ
OH
OH
OH
OH
OH
OH
OH
Haplotype B (G34D)
OH
Haplotype A (native)
PGINGFPGKDGRDGTKQEKGEPGQ
OH
OH
OH
Haplotype C (G37Q)
PGINGFPGKDGCDGTKGEKGEPGQ
OH
OH
Haplotype D (R32C)
OH
OH
OH
OH
OH
Low MBL plasma levels are caused by mutations in the promoter and/or coding region
in the MBL gene locus
A/A
1,000
MBL plasma
A/O
1000 ng/ml
 40%
100
10
1
O/O
100 ng/ml
 10%
C3
C3
3
C2
C2b
C4
2
C4b
C3b
C3b
C3b
4
1
MAC
C5-9
C5a
MBL-activating
surface
C4a
C3a
C2a
MBL is a Disease Modifier of Considerable Importance in the Context of
Secondary Immune Deficiencies
Plasma MBL activates complement by binding to carbohydrate structures presented by microorganisms. MBL levels were measured in
leukemia patients who were scheduled to undergo chemotherapy and MBL was related to the results of the chemo. Low MBL
concentrations are associated with serious infections related to chemotherapy (p<0.0001). CSI- clinically significant infections
Peterslund et. al., Lancet, 2001, vol 358, p 637
Complement activation
Recombinant MBL Functionally Equivalent to pMBL
500x10 3
pMBL (n=4)
rMBL (n=8)
400x10 3
300x10 3
200x10 3
100x10 3
0
1
10
MBL ng/m
Jensenius et.al., Bioch Soc Transactions, 2003, 31:763
100
Functional Analysis of the MBL/MASP-2 Complex
C 4a
Streptavidin
Eu3+
MAS P
C4
MBL
Biotin
C4b
Mannan
C4b
Correlation between MBL concentration in plasma and activity of MBL-MASP
complexes
C4 deposition (mU/ml)
10000
A/A
A/B
A/D
A/C
0/0
Linear regression
1000
100
10
1
1
10
100
1000
10000
MBL concentration (ng/ml)
C4 deposition (mU/ml)
MBL Reconstitution Does Not Rescue C4 Deposition
Patient+ rMBL
Sera
Healthy
control sera + rMBL
MBL deficient
MBL concentration (ng/ml)
Patient Outline
•Born 1967.
•No medical history until 1980 when diagnosed with ulcerative colitis
- treated with prednisolone.
•1996: erythema multiforme bullosum responding to prednisolone.
Suspect SLE - joint symptoms, myalgia, weakly positive anti-nuclear
antibodies.
•1995-1997 Several courses of severe pneumococcal pneumonia.
•Progressive lung fibrosis without vasculitis, alveolitis or granulomas.
Mutation in MASP-2/MAp19 Gene in CUB1 domain
Functional Analysis of the Mutated and Wild Type Recombinant MASP-2
MASP-2 (counts x 10-3/sec)
Functional Analysis of the Mutated and Wild Type Recombinant MASP2
30
A. MBL
B. L-ficolin
C. H-ficolin
50
20
45
18
25
40
16
35
20
14
30
12
15
25
10
20
8
10
15
6
4
10
5
2
5
0
0
0 25 50 75 100 125 0 25 50 75 100125 00 25 50 75 100125
ng MASP-2/ml
ng MASP-2/ml
ng MASP-2/ml.
Normal CUB1
ACC TTC GCG TCC GAC TAC TCC AAC GAG AAG CCG TTC
T
F
R S
D
Y S N
E
K
P
F
Mutant CUB1
105
G
ACC TTC GCG TCC GGC TAC TCC AAC GAG AAG CCG TTC
Conclusions
•The complement system comprises a group of serum
proteins.
•The three pathways converge in a common sequence of
events.
•Activation of the alternative and lectin pathways is antibody
independent.
•In addition to cell lysis complement mediates opsonization,
activation of inflammation, and clearance of the immune
complexes.
•Complement system can control the adaptive immunity
•Because of its ability to cause damage to the host organism,
the complement system requires a complex passive and active
regulatory mechanisms.