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• Skin• Respiratory Tract• Upper GI tract• Mucus• Cilia• Hair• Cough • Sneeze• Normal Flora• Sweat• Glands (lacrymal…tear)• pH (acidity)
Mucociliary escalator
Toll-like receptors of the Innate Immune System
Toll-like Receptors are important PPR (Pattern Recognition Receptors)
Prototypical TLR agonists and corresponding TLRs
TLR-6 TLR-9TLR-2 TLR-5TLR-1
Bacterial lipoprotein Flagellin
Bacterial CpG DNA
MD-2 TLR-4
LPS
TLR-3
dsRNAMycoplasmallipoprotein
Toll-like Receptor 4: The first human TLR discovered
LPS-nonresponsive mouse strains shown to harbor defective TLR4 gene.
TLR4: The long-sought signal transducer of LPS, cell wall component of Gram-negative bacteria
Cell membrane
LBP
LPS
CD14
TLR4MD2
IRAK
TRAF6
TAK1
IKKComplex
IkB
p65 p50
MyD88
NF-kB
Final product of cascade is the transcription factor NF-κB which leads to production of cytokines.
Bruce Buetler
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”• 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
Water Proteins4) CAPILLARY PERMEABILITY
1) BACTERIAL INVASION
7) KILLING/REPAIR
2) SIGNALS
6) PHAGOCYTOSIS
5) CHEMOTAXIS
Blood flow
Capillary
Signals
Macrophage
* Neutrophil
3) VASODILATION
Cytokines
The Innate Host Defense Response to Bacterial Infection of the Lung
Bonemarrow
G-CSF
TNF
ChemokinesG-CSF
Neutrophils
BacterialInvasion
MacrophagesAlveolus of Lung
Epithelial cells
Endothelial cells
Growth factor
Intrapulmonary bacterial challenge
0 24126 18
Cytokine response (TNF, IL-8, G-CSF)
Neutrophil recruitment into the Alveolar compartment
Percent viable bacteria remaining in the lung
The Normal Response to Intra-pulmonary Bacterial Infection
Cells Found in Bronchoalveolar Lavage Fluid
4 hours after intratracheal bacterial challenge
4 hours after intratrachealPBS
Neutrophil recruitment is essential for bacterial clearance.
Effect of Anti-TNF on Pulmonary Host Defenses against P. aeruginosa challenge
*
Ab-TNF Ab-TNF
*
U/m
l x 1
03
PMN
num
ber (
x106 )
2 h BAL TNF 4 h BAL PMN
5
10
15
0 0
2
4
6
8
10
% re
mai
ning
0
100
50
4 h Viable Bacteria
NIIgG
ND
Ab-TNFNIIgG
NIIgG
Cytokine production/secretion and neutrophil recruitment are critical to effective killing of invading bacteria. Same adverse effect with anti-chemokine or anti-GCSF
Water Proteins4) CAPILLARY PERMEABILITY
7) REPAIR
SIGNALS
6) PHAGOCYTOSIS
5) CHEMOTAXIS
Blood flow
Capillary
Signals
* Neutrophil
3) VASODILATION
Injury
Important Mediators of the Inflammatory Response
• Kinins• Complement• Blood clotting• Histamine• Eicosanoids• Platelet-activating factor• Cytokines to include
chemokines• Others
– Lysosomal enzympes– Nitric oxide– Reactive oxygen
intermediates
• 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
• 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 Secretion of Mediators
Intracellellular Killing of
microbes
Reg. of inflammatory
process
ExtracellularKilling of microbes
Reg. of overallbody 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
• Final Stage of Inflammation• Cell Division (tissue dependent)• Collagen secretion by fibroblasts• Angiogenesis• Imperfect remodeling scar
Anti-inflammatory Mediators• Exogenous
– 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
8000
4000
0
Plas
ma
Uni
ts/m
l
0 1 2 3 4Time (hours)
ControlStress
** *
Bacterial LPS
Epinephrine Infusion and the Bacteria-induced Plasma TNF Response
m l )TNF
(Uni
ts/m
l)
9000
6000
3000
0
Min. Post-LPS Administration60 90 120
Control Epinephrine
* * *
Stress Suppresses the LPS-induced TNF Response: Prevented by Mixed β & β2-Adrenergic
Antagonists
TNF at 90 min post-LPS
% o
f Con
trol
100
50
0
Stressb1 b2b-
Cntl
* *
Antagonist