Bacterial resistance to MAC

1
Bacterial resistance to MAC
The thick layer of peptidoglycan in
Gram-positive bacteria prevents the insertion of
MAC into cell membrane.
Gram-negative bacteria have thin layer of
peptidoglycan, and is susceptible to MAC lysis.
2
Complements are linked to other immune functions.
Lysis through MAC
bacteria
Phagocytosis by macrophages and neutrophils
Bacteria coated with C3b
B cells activation
C3b C3a
C3
Induce inflammation Recruit monocytes and
neutrophils
C5
C5b C5a
Ag
Ag
Clearance of immune complex to prevent autoimmune
disease
Ab
Immune complex
3
Complement Deficiency
deficient
Disease
C1
C4
Bacterial infections, SLE (systemic lupus
erythematosus)
C2
C3
Many kinds of bacterial infections
C5
C6,7,8
Meningococcal infections
C9
4
Patient deficient in components of MAC
(C5,6,7,8,9) are susceptible to Neisseria
infection.
Neisseria meningitidis (meningococcus, gram
negative bacteria) causes meningococcal
meningitis.
N. meningitidis
Nasopharynx
Blood
Meninges
5
Complement deficiency is revealed by CH50 assay.
Rabbit antibody against sheep red blood cell
surface antigens
Sheep red blood cell
5 x 108
Serum (complements)
37oC, 1 hour
Lysis of red blood cell
One CH50 is defined as the quantity of complement
required for 50 lysis of 5 x 108 red blood cell
at 37oC for 1 hour.
Patient 0 CH50 / ml
Serum added
normal
Complement titre 250 CH50 / ml
(ml)
1/500 dilution
2
y percentage of lysis
y
y
1
1-y
1
At 50 lysis, y0.5,
1-y
6
Regulation of Complement
Regulation of C1
bacteria
Serine protease
C1s, C1r
Active site serine
OH


Ser
C1s
C1r
C1INH
C1q
C1INH (C1 inhibitor)
O
Ser
C1INH
C4b C4a
C4
C2
C2b C2a
Suicide inhibitor
7
Deficiency in C1INH causes Hereditary
angioneurotic edema.
Recurrent swelling of skin and internal
organs. Swelling in the larynx could cause
suffocation.
C1INH inhibits additional serine proteases.
Injury to blood vessel
Factor XII
Vasoactive peptide
plasmin
Ag-Ab
Bradykinin
C1
Tissue swelling (edema)
Surrounding tissue
Blood vessel
Blood vessel
C2a
plasmin
Endothelial cell
Endothelial cells contraction
C2 kinin
Leakage of fluid from blood
Vasoactive peptide
8
Regulation of C3
immunity
Bb
C3b
Destruction of bacteria
bacteria
Autoimmunity
Alternative pathway
Bb
C3b
spontaneous
Destruction of human cell
C3b
C3
Human cell
thioester
Bb
C3b
Immunodeficiency
C3
free in solution
Depletion of C3
9
Factor H and I inactivate C3b.
Bb
Factor I cleaves C3b.
C3f
H displaces Bb.
C3c
Factor I
Factor I
H
H
C3b
iC3b
C3dg
Sialic acid
Human cell
Factor H binds to sialic acid.
Nonactivating surface
Bb
C3b
C3b
C3b
C3b
C3b
C3b
C3b
C3b
bacteria
No sialic acid
Activating surface
10
Regulators of Complement Activation (RCA)
Bb
Factor I cleaves C3b.
C3f
H displaces Bb.
C3c
Factor I
Factor I
C3b
iC3b
CR1
CR1
C3dg
Sialic acid
Human cell
Complement receptor 1 (CR1) is membrane protein.
Decay acceleration factor (DAF, on cell membrane)
displaces Bb from C3b on cell surface.
Similar regulation for C4b.
Regulators of Complement Activation (RCA) Factor
H, CR1, DAF, C4bp, MCP.
60 amino acid domain (short consensus repeats
(SCRs))
CR1
Factor H
11
Factor H and I also inactivate C3b in solution.
Bb
C3f
C3c
H
I
H
I
Bb
H
C3dg
iC3b
C3b
C3b
Factor H displaces Bb.
Factor I cleaves C3b.
CR1, DAF cannot control C3b in solution.
12
Factor H deficiency
Knockout of Factor H gene in mice depletes C3.
Mice
/-
/
-/-
Half H
No H
Normal H
Take blood sample Measure concentration of C3
normal
I
C3bi
C3bH
H
spontaneous
B, D
C3bBb
C3
C3b
Factor H deficiency
Deplete C3
C3b
13
Factor H deficient mice develop kidney disease.
14
Deposition of complements causes kidney damage.
Glomerular basement membrane (GBM) with double
contour appearance
Deposition of C3 and C9 in glomerulus.
15
Factor B deficiency rescue Factor H mutation.
normal
I
C3bi
C3bH
H
spontaneous
B, D
C3bBb
C3
C3b
Most C3 is in C3b form.
Deplete C3
C3b
Kidney damage
H deficiency
Mouse deficient in Factor B
Mouse deficient in Factor H
Mouse deficient in both Factor H and B
16
No kidney disease in Factor H and B double
deficient mice.
17
No deposition of C3 and C9 in the kidney of
double deficient mice
18
Patients deficient in Factor H or I have similar
symptoms.
The patient suffers from recurrent infections
with many kinds of bacteria.
8 mg/dl C3
Low level of C3 (27 mg/dl, normal range 97-204
mg/dl)
Acquired C3 deficiency
27 mg/dl
19 mg/dl C3b
No factor I in serum
Rapid conversion of C3 into C3b
125I-C3 concentration in plasma
Patient
Infuse with Factor I
Normal people
injected with 125I-labelled C3
injected with 125I-labelled C3
Patient infused with factor I
patient
Take blood sample Measure 125I-C3 level
Take blood sample Measure 125I-C3 level
Time after injection of 125I-C3
19
Summary
skin
Regulators prevent excessive activation of
complements and damage of host cells
complement
Bacteria tagged with C3b
Destruction by other immune functions
Lysis by MAC
(Gram negative bacteria)
20
Questions
Which type of bacteria is susceptible to lysis by
complements?
How are complement activation limited to
bacteria in the three pathways?
How do factor H and I control complement
activation?
Relevant part in textbook
p177-183
21
Macrophage
skin
Macrophage
complement
Destruction by other immune functions
Lysis by MAC
22
Macrophages are generated from bone marrow.
Hematopoietic stem cell (HSC)
Bone marrow
Primary lymphoid organ
Myeloid progenitor
Granulocyte-monocyte progenitor
Monocyte
Blood
Monocyte
tissue
Macrophage
23
Blood
Plasma 55
Red blood cell
white blood cell platelet lt1
24
Microphages are distributed in many tissues.
Bone marrow
HSC
monocyte
liver
brain
Microglial cell
Kupffer cells
Monocyte in blood circulation
lung
Alveolar macrophage
Many tissues
Resident tissue macrophage
25
Recognition of pathogens
Pathogen Associated Molecular Pattern (PAMP)
Lipoteichoic acids
Present in microbes, but not in host cells.
Essential for the survival of microbes.
peptidoglycan
chromosome
Cytoplasmic membrane
Cell wall
Gram-positive
Lipopolysaccaride (LPS)
flagellum
peptidoglycan
Cytoplasmic membrane
Gram-negative
26
Pattern Recognition Receptor (PRR)
Toll-Like Receptors (TLR)
extracellular ligands
TLR-1, 2, 4, 5, 6
Cytoplasmic membrane
cytoplasm
TLR-3, 7, 8, 9
endosome
endocytosed ligands
27
(LTA)
(PG)
28
Signal transduction of TLR
ligand
1. Ligand binding induces dimerization of TLR
TLR
membrane
TIR domain (Toll IL1 receptor)
Cytoplasm
2. Adaptor proteins (MyD88) bind to
cytoplasmic domain of receptor.
IRAK1 IRAK4
3. Activation of kinases
Stronger signals
Phosphorylation
Amplification
Cascade of protein activation
More pathways
Ubiquitination
4. Activation of transcription factors
Nucleus
5. Transcription of genes for immune function