From Blood to Host Defense Innate Host Defense

From Blood to Host Defense Innate Host Defense

Gregory J. Bagby, [email protected]: 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• 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