Lecture 12 & 13: The First line of Defense (continued)
Complement, Chemokine and Cytokines (Chapter 3)
Characteristics and Roles of Complement
What is complement? Common features of complement activation i.e. Opsonizing
COVERED LAST LECTURE
Phagocytosis, MAC complex
Complement activation can be triggered by 3 pathways
The classical pathway mediated by antibody
The classical pathway mediated by collectins
The alternative pathway – selection of bacterial cells
Summary
Roles of cytokines and chemokines in directing the phagocytic response
What are cytokine & chemokines, which cells produce them, when are they released,
and what do they trigger?
How LPS triggers cytokine production in a macrophage
CD14 mediates cytokine release through Toll-like receptors
Some effects of cytokine release
Additional effects of cytokine release
Overview of innate response and the roles of complement, cytokines and chemokines
Septic shock
A more thorough look at septic shock
1
1
Complement activation can be triggered in
three ways
i/ Collectin mediated activation
Mannose-binding lectins - made as
part of the acute phase response by
the liver.
Bind mannose on bacterial surfaces
Induce clumping of bacteria and
complement cascade
ii/ Classical Pathway
Antibodies of the specific
defense system bind bacteria
specifically. A link between
innate and specific immunity
iii/ Alternative pathway
Certain bacterial molecules triggers
the complement cascade directly.
Eg, LPS & TA
Complement cascade triggered by
C3b binding to the bacteria surface
2
2
Common features of all three pathways
• All activation pathways result in the production of C3a
C3b C5a C5b.
• Both C3a and C5a stimulate mast cells to release their
vasodilatory contents.
• C5a acts together with cytokines to guide PMNs and
macrophages to the infection site.
• C3b bind to the surface of a bacterium making it easier
for phagocytes to ingest = Opsonization.
• C5b triggers synthesis of the membrane attack complex
(MAC).
• Complement activation also leads to the agglutination
(clustering or clumping) of invading bacteria, which
increases the efficiency of phagocytosis.
3
3
Opsonizing phagocytosis
Opsonization can be triggered by
complement or antibodies
Definition of Opsonization = smothering or
coating
Without opsonization phagocytes have
difficulty engulfing a bacterium
Bacteria coated with C3b can stick to
phagocyte more readily because
phagocytes have receptor that bind C3b
Antibodies also acts as opsonins, the Fc
portion is recognized by phagocyte
receptors
4
4
Membrane Attack Complex (MAC)
•Another feature of all complement activation pathways is direct
killing of bacteria
•C5b recruits C6 C7 C8 & C9
•This forms a membrane
damaging complex called MAC
Result: Punches holes in the
membranes of enveloped viruses,
gram negs and some gram pos.
Effect:: Kills most bacteria
and inactivates viruses.
5
5
Classical Pathway – mediated by antibodies
6
6
Lectin pathway - mediated by
Mannose Binding lectins (MBLs) &
Ficolins (FCNs)
MBL - a member of Collectin family.
Collectins are calcium-dependent lectins
Lectins are proteins that bind specific sugars in the presence of Ca2+
Mannose is routinely found on bacterial surfaces but not human surfaces
Ficolins bind N-acetyl glucosamine (NAG) also found on bacteria (function similarly to MBL)
The alternative pathway
•C1 , C2 and C4 are not needed.
•In this pathway C3 is King
On human cells
On bacterial cells
Serum
protein D
8
8
Role of iC3b?
In all three pathways it is important to keep the production of C3a, C3b, C5a and C5b
under control
To do this, most C3b molecules are proteolytically cleaved to produce iC3b.
iC3b is an effective opsonin, but fails to form the C3 convertase or C5 convertase
complex.
Summary of complement
•Induces vasodilation
•Targets bacteria for phagocytosis by PMN and macrophages – two ways
opsonin production and agglutination
•Kills bacteria directly, (MAC)
•Guides phagocytes to site of infection
•Complement activation can occur by 3 pathways
•Complementation activation requires a complex set of proteolytic interactions
•Consequently, the Complement cascade is tightly regulated
10
10
How do PMNs know when to leave the
blood and where to go?
Complement system
Activated by contact with invading bacteria or antibodies bound to invading
bacteria
Cytokines/Chemokines system
Cytokines and chemokines - made by a number of different cell types, including
monocytes, macrophages, endothelial cells, lymphocytes and fibroblasts
Cytokines- proteins or glycoproteins (8-30KDa) that mediate the inflammatory
response to antigens and tissue damage, they also activate cells of the specific
immune system
Chemokines - are small glycopeptides (8-10KDa) that guide phagocytes to an
infection site also play a role in orchestrating the immune response
11
11
A well studied example: How LPS triggers
Cytokine release
Cytokines are released
when bacteria or bacterial
products interact with
cytokine producing cells
Example: A macrophage
interacts with LPS
12
12
Cytokines & Chemokines help to mediate
the inflammatory response
Integrins bind
to ICAMs to
trigger
margination
Both C3a and C5a
stimulate mast cells
to release their
vasodilatory
contents (PAF too)
13
13
Margination & Extravasation video
https://www.youtube.com/watch?v=XylVhCRQATk
14
14
Production and Activity of selected Cytokine/Chemokines
Cytokine
Producing cell(s)
Target cell(s)
Function
GM-CSF*
Th cells
Progenitor cells
Growth and differentiation of monocytes and DCs
IL-1a**
Monocytes
Th cells
Costimulation
IL-1b**
Macrophages, B cells & DCs
B cells
NK cells
Various
Maturation, proliferation,
Activation
Inflammation, acute-phase response, fever
IL-2
Th1 cells
Activated T and B cells, NK cells
Growth, proliferation, activation
IL-3*
Th cells and NK cells
Stem cells,
Mast cells
Growth, differentiation
Growth, histamine release
IL-4
Th2 cells
Activated B cells, Macrophages,
T cells
Proliferation, differentiation, IgG1 & IgE synthesis
MHC-II
Proliferation
IL-5
Th2 cells
Activated B cells
Proliferation, differentiation, IgA synthesis
IL-6
Monocytes, Macrophages,
Th2 cells, Stromal cells
Activated B cells
Plasma cells
Stem cells
Various
Differentiation into plasma cells
Antibody secretion
Differentiation
Acute phase response
IL-7
Marrow stroma, thymus stroma
Stem cells
Differentiation into progenitor B and T cells
IL-8**
Macrophages, endothelial cells
Neutrophils
Chemotaxis
IL-10
Th2 cells
Macrophages
B cells
Inhibit cytokine production
Activation
IL-12
Macrophages, B cells
Activates Tc cells,
NK cells
Differentiation into CTLs (with IL-2)
Activation
IL-13
Live Kupffer cells, lung macrophages,
kidney epithelial cells
Macrophages
Inhibit inflammatory cytokine production
IFN-α
Leukocytes
Various
Inhibit viral replication, MHC-I expression
*
*
*
Production and Activity of selected Cytokine/Chemokines
(cont.)
Cytokine
Producing cells
Target cells
Function
IFN−β
Fibroblasts
Various
Inhibit viral replication, MHC-I expression
IFN-γ∗∗
Th1 cells, Tc cells, NK cells
Various
Activated B cells,
Th2 cells, Macrophages
Inhibit viral replication
Ig class switch to IgG2a
Inhibit proliferation
Pathogen elimination
MIP-1α
Macrophages
Monocytes, T cells
Chemotaxis
MIP-1β
Lymphocytes
Monocytes, T cells
Chemotaxis
TGF-β
T cells, monocytes
Monocytes, m’phages,
activated m’phages, activated B
cells, Various
Chemotaxis,
IL-1 synthesis
IgA synthesis
Inhibit proliferation
TNF-α∗∗
Macrophages, mast cells, NK cells
Macrophages Tumor cells
ICAM and cytokine expression
Cell death
TNF-β
Th1 and Tc cells
Phagocytes,
Tumor cells
Phagocytosis, NO production
*Early release of monocyctes & PMNs from bone marrow
**Other early cytokines that stimulate monocytes and granuloctyes to leave bloodstream
head to site of infection
Anti-inflammatory cytokines – downregulate the production of TNF-α and reduce killing
activities of phagocytes
A new view of inflammation
Complement activation, cytokine release, phagocyte
transmigration, production of prostaglandins and
leukotrienes cause tissue INFLAMMATION
Commons symptoms of localized inflammation include:
Redness, swelling, heat, pain
Resolution?
If phagocytes are successful at clearing the invading
bacterium different cytokines start to predominate.
IL-4, IL-10, IL-13
Leads to downregulation of TNF-α, which reduces the
killing activities of phagocytes.
Return to normal
17
17
Other activities of cytokine release
• Many of the common symptoms of infectious
disease can be attributed to the action of
proinflammatory cytokines
IL-1 & TNF-α stimulate the hypothalamus and adrenal glands
Fever
Somnolence – strong desire for sleep
Malaise – general feeling of sickness IL-6 stimulates the liver
Anorexia – loss of apetite
Stimulate production of acute phase
proteins
TNF-α and other cytokines
Eg. Complement proteins, LPS
stimulate muscle cells
binding proteins, collectins
Weight loss, muscle wasting, chills
Transferrin = Decrease in blood iron
content
18
18
Summary
Complement, Cytokines and Chemokines impact on the innate
immune system
19
19
… and that, ladies and gents was the
inflammatory response!!
20
20
When things go wrong
The dark side of the non-specific defenses:
Septic shock
• Shock – acute circulatory failure leading to organ
failure
• Septic shock is a form of shock that results from
bacterial infection
• 500,000-750,000 patients suffer from septicemia
each year in the US, 50% of these die
• There are 4 stages of septic shock
•
•
•
•
i) Systemic inflammatory response syndrome (SIRS)
ii) Sepsis,
iii) Severe sepsis
iv) Septic shock
21
4 stages of septic shock – descriptions of each
Systemic Inflammatory Response Syndrome (SIRS) –
Temperature >38 or <36 degrees C; elevated heart rate; elevated respiratory
rate; unnaturally high or low neutrophil counts
* At this stage the administration of an appropriate antibiotics can prevent
septic shock, but early diagnosis is difficult & the antibiotic to use is not always
clear
Sepsis – SIRS with a culture-documented case of infection in the blood -
bacteremia
Severe Sepsis – organ dysfunction and very low blood pressure
Septic Shock – low blood pressure despite fluid administration
Death
rate
exceeds
70%
22
Septic Shock continued
• The body usually goes to great lengths to ensure that the
inflammatory response occurs only in one tiny part of body
• Septic shock occurs when the inflammatory response is triggered
throughout the whole body
• Occurs when bacterial load in the bloodstream is so high that
complement activation, cytokine release, and the coagulation
cascade occur throughout the whole body.
• Progress of the condition can be extremely rapid
• For hospitals this is a big health and economic problem (Annual
Hopital Costs $5-10 billion)
23
DIC – often seen as
blackish or reddish
skin lesions
(petechiae)
Summarized Fig 3-13
24
Lecture 14:
Introduction to the adaptive immune system –
immunoglobulins
Study Guide
Overview of the specific immune system
Sequence of events during an acute infection;
Importance of both innate and adaptive immune
systems
Key features of the adaptive immune system
Specificity, Memory and Tolerance
Components of the adaptive immune system:
Immune cells and immunoglobins
Immunoglobulins
What are Igs? Structure; Domain structure;
Terms antigen and epitope; 3 major functions of Igs;
Structure and function of different Igs (serum and
secreted)
Avidity= affinity + valence
25
Major components of immune responses
Immune responses
Second line of defense
Adaptive, acquired, specific
Naturally
acquired
First line of defense
Innate, natural, non-specific
Active
(infection)
Mechanical
barriers
Chemical
barriers
Passive
(maternal
antibody)
Artificially
acquired
Active
(vaccination)
Passive
(Immune
Serum)
Microbiological
Inflamm
-ation
Inter
-ferons
Phago
-cytosis
Complement
26
Course of a typical acute infection
27