From Blood to Host Defense
Innate Host Defense
Gregory J. Bagby, Ph.D.
gbagby@lsuhsc.edu
Office: 310 (CSRB)
From Blood to Host Defense
• Blood
– Components and function
– Hemostasis and clotting
• The host defense system
– General overview
– Innate immune system
• pathogen recognition
• inflammatory response
– Adaptive immune system
• Humoral immune system and antibodies
• Cell-mediated immune system
Innate Immune Defense
• Defenses at the body surfaces
• Response of host defense cells that have an innate
ability to respond to foreign molecules or altered/injured
self
– Innate defense cells recognize some general property of foreign
substances or cells
– Such identity tags are often found in particular classes of
carbohydrates or lipids in microbial cell walls – pattern recognition
receptors
• The inflammatory response is part of innate host defense
– General sequence of inflammation
– Lung inflammatory response to eradicate infection
– Non-infectious inflammatory response
• Type I interferons
• Tissue repair
• Anti-inflammatory mediators
Body Surfaces Minimize
Entry of Pathogens
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Skin
Respiratory Tract
Upper GI tract
Mucus
Mucociliary escalator
Cilia
Hair
Cough
Sneeze
Normal Flora
Sweat
Glands (lacrymal…tear)
pH (acidity)
Toll-like receptors of the Innate Immune System
Toll-like Receptors are important PPR
(Pattern Recognition Receptors)
Bacterial
lipoprotein
TLR-1
Mycoplasmal
lipoprotein
TLR-2
TLR-6
dsRNA
TLR-3
LPS
MD-2
Flagellin
TLR-4
TLR-5
Prototypical TLR agonists and corresponding TLRs
Bacterial
CpG DNA
TLR-9
Toll-like Receptor 4: The first human TLR discovered
LPS
Bruce Buetler
TLR4
MD2
LBP
CD14
TLR4: The long-sought signal
transducer of LPS, cell wall
component of Gram-negative bacteria
LPS-nonresponsive mouse strains
shown to harbor defective TLR4 gene.
Final product of cascade is the
transcription factor NF-κB which
leads to production of cytokines.
Cell membrane
MyD88
IRAK
TRAF6
TAK1
IKK
Complex
NF-kB
IkB
p65 p50
Inflammatory Response
• Local (or systemic) response to infection or injury
– The local manifestations of inflammation are redness, swelling,
heat, and pain
– Systemic manifestations are fever, ache all over feeling,
mallaise.
• Purpose it to initiate destruction or inactivation foreign
invaders or damaged/abnormal cells, and to set the
stage for tissue repair
Cell Types of Innate Immunity
“players of the game”
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Neutrophils - blood
Eosinophils – blood
Basophils – blood
Monocytes – blood
Mast Cells – tissues
Macrophages – tissues
– Resident macs. mostly barrier
tissues (lung skin, GI tract, liver)
– Dendritic cells - tissues
• Natural Killer Cells – blood and tissues
Sequence of Events in Inflammatory
Response to Bacteria
• Bacterial invasion and recognition by macrophages and
other cells.
– Production of pro-inflammatory cytokines
– Phagocytosis of invading/damaged cells
• Microvascular damage and changes
– Entry and activation of plasma proteins that amplify inflammatory
response
– Vasodilation of microcirculation to increase blood flow (red & heat)
– Local increased vascular permeability of capillaries and venules
resulting in fluid leak including plasma proteins (edema)
• Chemotaxis – movement of leukocytes into infected area
Initiation of host response
• Killing and phagocytosis by neutrophils
• Set stage for tissue repair
Macrophage
1) BACTERIAL INVASION
2) SIGNALS
7) KILLING/REPAIR
Cytokines
4) CAPILLARY PERMEABILITY
Water
Proteins
3) VASODILATION
6) PHAGOCYTOSIS
Signals
5) CHEMOTAXIS
Blood
flow
Capillary
* Neutrophil
The Innate Host Defense Response to Bacterial
Infection of the Lung
Bacterial
Invasion
Macrophages
Alveolus
of Lung
TNF
Epithelial
cells
Chemokines
G-CSF
Endothelial
cells
Neutrophils
Bone
marrow
G-CSF
Growth factor
The Normal Response to
Intra-pulmonary Bacterial Infection
Intrapulmonary bacterial challenge
Percent viable bacteria remaining in the lung
Neutrophil recruitment into the
Alveolar compartment
Cytokine response (TNF, IL-8, G-CSF)
0
6
12
18
24
Cells Found in
Bronchoalveolar Lavage Fluid
4 hours after intratracheal
PBS
4 hours after intratracheal
bacterial challenge
Neutrophil recruitment is essential for bacterial clearance.
Effect of Anti-TNF on Pulmonary Host Defenses
against P. aeruginosa challenge
Cytokine production/secretion and neutrophil recruitment are critical to effective
killing of invading bacteria. Same adverse effect with anti-chemokine or anti-GCSF
5
ND
0
NI
Ab-TNF
IgG
10
8
6
4
2
0
4 h Viable Bacteria
100
*
% remaining
10
4 h BAL PMN
PMN number (x106)
U/ml x 103
15
2 h BAL TNF
50
*
0
NI
Ab-TNF
IgG
NI
Ab-TNF
IgG
SIGNALS
Injury
7) REPAIR
4) CAPILLARY PERMEABILITY
Water
Proteins
3) VASODILATION
6) PHAGOCYTOSIS
Signals
5) CHEMOTAXIS
Blood
flow
Capillary
* Neutrophil
Important Mediators of the Inflammatory Response
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Kinins
Complement
Blood clotting
Histamine
Eicosanoids
Platelet-activating factor
Cytokines to include
chemokines
• Others
– Lysosomal enzympes
– Nitric oxide
– Reactive oxygen
intermediates
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Plasma
Plasma
Plasma
Mast cells, injured cells
Many cells
Many cells
Macrophages and other
immune and non-immune cells
• Injured cells, neutrophils,
macrophages
Vasodilation and Increased Permeability
• Many mediators – kinins, histamine,
completment
• Two purposes
– Increase delivery of plasma mediators and cellular
participants in the inflammatory response
– Increased diffusion of mediators and
migration/diapedesis of leukocytes through the
capillary or venule wall.
Functions of the Complement Proteins
• > 30 identified plasma proteins
• Activated by infection, damage (inflammation) or Ab-Ag
complexes
Killing of Microbes by
Phagocytosis
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Phagocytosis is engulfing of
microbes by cells such as
macrophages and neutrophils
Phagosome + lysosome =
Phagolysosome
Enhanced by host substances that bind
to the microbe – opsonin (prepare for eating)
– Complement – C3b
– Antibody-Antigen complex
– C-reactive protein
Killing of Microbes by Extracellular Killing
• Phagocytes can also kill microbes by secreting
antimicrobial substances
– nitric oxide
– reactive oxygen intermediates
• Activated complement proteins
– Membrane attack complex (MAC) – inserts into wall of microbe
membrane to form a pore-like leaky channel to disrupt the
intracellular ionic environment.
Role of the Macrophage in Host Defense
• Play a critical role in recognizing invading bacteria via
TLR.
• Secrete antimicrobial chemicals (reactive oxygen
intermediates)
• Initiate inflammatory cascade by producing cytokines,
chemokines and growth factors.
• Able to process and present antigen to Helper T cells
(but Dendritic cells are better).
• Engulf (phagocytosis) and neutralize/kill pathogen.
Accelerated via antibody-antigen complexes
(opsonization)
Local and Systemic Consequences of Microbe
Contact with Phagocytes
Microbial Contact with Phagocytes
Phagocytosis
Intracellellular
Killing of
microbes
Secretion of Mediators
Reg. of
inflammatory
process
Extracellular
Killing of
microbes
Reg. of overall
body response to
infection
Activation of clotting &
anticlotting pathways
Role of Type I Interferons in
Innate Host Defense
• The innate system also
participates in host
defense against viruses
• Virally infected cells
secrete type I interferons
• Type I interferon binds
to uninfected cells to
induce synthesis of
antiviral proteins which
inhibit viral replication
Tissue Repair
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Final Stage of Inflammation
Cell Division (tissue dependent)
Collagen secretion by fibroblasts
Angiogenesis
Imperfect remodeling  scar
Anti-inflammatory Mediators
• Exogenous
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Synthetic glucocorticoids
Non-steroidal anti-inflammatory (e.g. aspirin, ibuprofen)
Catecholamines that are Beta2 agonists
Pro-inflammatory cytokine antagonists (Ab-TNF or
sTNF-R)
• Endogenous
– Anti-inflammatory cytokines – IL-10
– Glucocorticoids (cortisol)
• Rodent adrenalectomy –
– Increase stimulation of LPS-induced TNF production by
macrophage
– Reversed by glucocorticoid administration
• Catecholamines
The plasma TNF Response to the TLR4 Ligand LPS
12000
Bacterial LPS
Control
Plasma Units/ml
Stress
8000
4000
*
*
0
0
1
*
2
Time (hours)
3
4
Epinephrine Infusion and the Bacteria-induced
Plasma TNF Response
6000
3000
l)
m
TNF (Units/ml)
9000
0
*
*
*
60
90
120
Min. Post-LPS Administration
Control
Epinephrine
Stress Suppresses the LPS-induced TNF Response:
Prevented by Mixed β & β2-Adrenergic Antagonists
TNF at 90 min post-LPS
% of Control
100
50
*
0
Cntl
-
*
b b1 b2 Antagonist
Stress