Immunology Exam I Flashcards
Where is the immune system?
Blood Stream
Primary Lymphoid Organs
Thymus - T cells
Bone Marrow - B cells
Site where white blood cells develop
Secondary Lymphoid Organs
Spleen
Lymph nodes
Tonsils
Hemopoietic stem cell –> common lymphoid progenitor –>
B cell / Plasma cell
Hemopoietic stem cell –> common lymphoid progenitor –> NK/T cell precursor –>
T cell/Effector cell
Common Myeloid Progenitor
I. Granulocyte
- neutrophil
- basophil
- eosinophil
II. Unknown Precursor
- monocyte –> dendritic cell + macrophage
- mast cell
cytokines
Molecules secreted by one cell and acting on another.
“Hormones of the immune system”
Can cause inactivation and Activation
Lymphocytes
T cells, B cells, NK cells
Proportion of Neutrophils
40-75%
Proportion of eosinophils
1-6%
Proportion of Basophils
<1%
Proportion of monocytes
2-10%
Proportion of Lymphocytes
20-50%
Cells of the Innate Immune System
Phagocytes
Granulocytes
NK Cells
Phagocytes
Macrophages
Neutrophils
Dendritic Cells
Granulocytes
Neutrophils
Basophils
Eosinophils
Mast Cells
Cells of the Adaptive Immunity
B and T cells
Proliferate + expansion of cells bound to the virus
Adaptive Immunity
Cells w/ exquisitely specific receptors for a potentially unlimited # of targets
T and B cells
Effective only after a delay of several hours/days
Recognizes only specific species
Immunity Increases because more memory cells remember the pathogen
Innate Immunity
Molecules and cells that distinguish host from infectious agents by recognizing conserved motifs
- fx: all gram negative bacteria
Activated within min to hrs of exposure
Not significantly increased after several exposures
Forms of Adaptive Immunity
Humoral Immunity - B cells - Antibody Response
Cell Mediated Immunity - T cells + cytokimes
B cells
Secreted or on cell surface
Two antigen binding sites
T cells receptor
Always on cell surface
One Antigen binding site
Antigen
A molecule (often derived from a pathogen) recognized by the immune system
Antibody
protein produced by B-cells, binds very specifically to a given antigen; also called immunoglobin
Epitope
Specific region of antigen. The region of an antigen that is bound to an antibody
Neutrophils are stored in
bone marrow and secreted to epithelial region upon infection
Macrophage Uptake
Uptake of bacteria causes change in gene expression of that macrophage leading to production of inflammatory cytokines
Transition from Innate –> Adaptive
Begins with the immigration of dendritic cells to the draining lymph nodes.
Myeloid lineage
Mast cell
Basophil
Eosinophil
Neutrophil
Macrophage
Dendritic Cell
Cells capable of phagocytosis
Dendritic Cells
Macrophage
Neutrophil
Eosinophils
Bi-lobed
Granules stain brightly with the dye, Eosin (ACID LOVING)
Granules contain a variety of toxic enzymes and histamine
Best known for combatting multicellular parasites or helminths (parasitic worms)
Basophils
Stain dark purple; with basic dye
Least common granulocyte
Granules contain histamine, proteoglycans (heparin and chondroitin) and proteolytic enzymes
Important source of the cytokine IL-4 which is central to allergic reactions (Starting the reaction)
Express IgE receptors like mast cells
Mast Cells
Major mediator of type I hypersensitivity rxns (Allergy)
Localized in tissues where they mature
Very similar to basophils
Granules contain histamine and heparin
Express receptors of IgE
Macrophages and Dendritic Cells
Phagocytic
Macrophages have bactericidal activity and can be present antigens under certain conditions
Dendritic cells are phagocytic, but not known for bactericidal activity
Dendritic cells are “professional antigen presenting cells” - they can stimulate T cells
Neutrophils
Poly-morpho nuclear cells (PNM)
Abundant in the blood
24h half life ( constantly regenerated)
Migrate from blood to sites of infection rapidly
Potent killers of pathogens
- phagocytosis
- granules loaded with degradative enzymes
- produce reactive oxygen and nitrogen radicals and other bactericidal compounds
Three Major Neutrophil Functions
Migration
Phagocytosis
Respiratory Burst (NADPH oxidase)
Migration
Leukocyte extravasation –> Movement of leukocytes out of the circulatory system and toward sites of inflammation or infections
Selectins
Enable initial attachment of leukocytes from the bloodstream
Low Affinity Integrin - Adhesion Molecule
LFA-1
Can do both high and low affinity conformation
Chemokine sends out information to the neutrophil to change the conformation of LFA-1 to high affinity conformation –> slows down.
Results in ICAM-1 –> Leukocytes stops
Phagocytosis and degranulation
Microbes bind to phagocyte receptors on neutrophil
Phagocyte membrane zips up around the microbe
Microbe ingested in phagosome
Fusion of phagosome with lysosome
Killing of microbes by ROS, NO and lysosomal enzymes in phagolysosomes
Phagocyte oxidase/ NADPH
yields Reactive Oxygen Species (ROS)
iNOS yields
Nitrogen radicals (NO)
What are in granules?
Enzymes –> degrade bacterial components
Defensins –> poke holes in bacterial membranes
Lactoferrin –> sequester iron away from bacteria
NADPH oxidase components
Secondary (specific) granules
Respiratory Burst
mediated by NADPH oxidase
Production of bactericidal compounds begins
Components of the NADPH oxidase complex
Localized to the membrane and in the cytoplasm (inactivated complex)
When cell becomes activated, these two components become co-localized and this is when the production of the radicals occur.
Gives rise to hydrogen peroxide and hypochlorous acid
bacterial killing cell types
macrophages and neutrophils
differ: neutrophils are short lived and produce oxygen radicals
Macrophage: produce mostly nitric oxide (nitrogen radical)
Neutrophil Death
apoptosis lyses the cell nucleus and plasma membrane. these small parts can be eaten by macrophage ingestion to clear out the dead neutrophil
If there has been an infectious event, neutrophils exist the body as pus
Chronic Granulomatous Disease (CGD)
NADPH oxidase defects
Chediak-Higashi syndrome
Phagocytosis and granule defects
Leukocyte Adhesion Deficiency (LAD)
deficiency in adhesion molecules, migration into tissues is minimal
zymogens (complement system)
an enzyme that is synthesized in serum, in a biologically inactive form, and must be cleaved in order to become biologically active
Function of complement system
- Control of inflammation (recruitment of phagocytes)
- Enhanced uptake and clearance (Opsonization)
- Lytic attack of cell membranes (killing bacteria)
Classical Pathway Activation
Antigen:antibody complex
MBL Pathway Activation
Lectin binding to pathogen surfaces
Alternative Pathway Activation
Pathogen Surfaces
What pathway happens spontaneously on pathogen surfaces?
The Alternative Pathway
All three pathways come together, resulting in
Complement activation
The Classical Pathway
Initiated by antibody or C reactive Protein (CRP) binding to pathogen surface
Initiation complex includes C1 components (C1q, C1r, C1s)
C1r + C1s
enzymatic components. must be cleaved to facilitate the cascade continuing
C1q
stalk like legs. attaches to the antigen binding site.
C1q is recruited to the bacterial surface.
Followed by activation of C1r and C1s
example of anaphylatoxin
c3a
What is an anaphylatoxin
molecule that recruits phagocytes to the site
c3b serves as an
opsonin
The MBL (mannose binding lectin) pathway is initiated by
MBL binding to specific mannose and fucose residues on pathogen surface ( consistent pattern)
What does the MBL initiating complex consist of?
MASP (MASP1, MASP2), proteins, and MBL
Step 1 of MBL (after initation)
Activated MASP2 cleaves C4 into C4a and C4b. Some C4b binds covalently to the microbial surface
Step 2 of MBL (after initiation)
Activated MASP 2 also cleaves C2 into C2a and C2b
Step 3 of MBL (after initiation)
C2a binds to surface C4b forming the classical C3 convertase C4b2a
Step 4 of MBL (after initiation)
C4b2a binds C3 and cleaves it to C3a and C3b. C3b binds covalently to the microbial surface
The Alternative Pathway Characteristics
I. Activation cascade is initiated without a ligand binding molecule
II. Complement is fixed on bacterial surfaces spontaneously
III. C3 Convertase is distinct from classical and MBL pathways
Spontaneous Activation og C3 in Plasma
The alternative pathway:
C3 is spontaneously hydrolyzed in serum and the end result is C3b which can attach to the bacterial membrane and liberation of C3a which acts as a chemoattractant (anaphylatoxin) to phagocytes
Enzymes in the Alternative Pathway
B and D factor
C3a anaphylatoxin
Tells the phagocytes to move to the site of the infection
The alternative C3 activation is
self perpetuating
Classical + MBL C3 Convertase Components
C2a + C4b
Alternative C3 Convertase Components
Bb + C3b
C3a and C5a
Anaphylatoxins that act on blood vessels to increase vascular permeability
Move cells in a chemotactic fashion
Responsible for moving plasma, monocytes and proteins out of the vessel to engulf the nearby bacteria
CR1 receptor
Binds the bacteria (tagged with C3b) to the macrophage surface
The macrophage performs endocytosis
macrophage membrane fuse, creating a membrane bound vesicle, the phagosome
lysosomes fuse with the phagosomes forming the phagolysosome
C3 cleavage leads to
C3a –> recruits phagocytes
C3b –> tags bacterium for destruction (oposonization or membrane attack)
C5b
binds to the bacterial membrane and initiates the assembly of “the membrane attack complex “ also called MAC.
C5b binds firstly to
C6 and C7. These allow the C5 protein to anchor into the bacterial surface
Then C8 is recruited
When C8 has been recruited..
Many C9 molecules are recruited to come in and form a pore in the bacterial surface.
Membrane Attack results in
Leakage of the contents of the bacteria and disruption of the chemo-osmotic barrier and the bacteria dies
Lytic Membrane Attack components
C5b - initiating ligand
C6
C7
C8
C9 - pore forming
Which inhibitor acts in the early complement cascade?
C1 inhibitor (C1INH)
binds to activated C1r, C1s, removing them from C1q, (Shuts off the classical pathway)
and to activated MASP-2, removing it from MBL (Shuts off MBL pathway)
Which inhibitor acts in the middle of the complement cascade?
Factor H (H) and Factor (I)
When one is lacking, the other cannot work.
Factor H
binds C3b, displacing Bb; cofactor for I
Stops cascade from proceeding to membrane attack
Factor I
Serine protease that cleaves C3b and C4b; aided by H, MCP, C4BP, or CR1
Which inhibitor works in the late complement cascade?
CD59 (Protectin)
Prevents formation of membrane attack complex on autologous or allogeneic cells. Widely expressed on membranes
Binds to C9 - preventing pore formation
H and I inactivation of C3b
C3b unable to continue in its cascade towards membrane attack, when I comes in and cleaves it. It can no longer be a ligand leading to membrane attack
Factor I and H, DAF, MCP
inhibit complement on host cell membrane
results in iC3b
Properdin
helps complement work on bacterial membranes.
stabilizes C3 convertase C3bBb on pathogen surface
How does CD59 work?
CD59 comes in and binds to C5b678 complex and prevents recruitment of C9 to form the pore
The Acute Phase Response
IL6 cause the liver to produce more MBL and CRP and fibrinogen. Increases the complement cascade components
Job of C3a
Recruitment of inflammatory cells
C3b serves as an
opsonin
Effects of Deficiency: Immune-complex disease
C1, C2, C4
Effects of deficiency: Susceptibility to capsulated bacteria
C3
Effects of Deficiency: Susceptibility to Neisseria
C5-C9
Effects of Deficiency: Similar effects to deficiency of C3
Factor I
PAMPs
Pathogen associated molecular patterns
PAMP of (gram +)
peptidoglycan, lipotheichoic acid
PAMP bacteria
Hypomethylated CpG DNA
Gram (-) PAMP
Lipopolysaccharide
PAMP of motile organisms
Flagella –> Flagellin
PAMPS are recognized by
Pattern recognition receptors (PRR) on cells of the innate immune system:
Macrophages, NK cells, neutrophils, dendritic cells
PRRs include:
TLR (Toll like receptors)
Cytosolic Receptors
Uptake receptors
Facilitate uptake of particles: complement receptors, scavenger receptors, mannose receptors
Signaling Receptors
Recognizes bacterial PAMPs and induce activation of the cell through signaling cascades leading to changes in gene expression
TLR, NOD-like receptors, RIG-I-like receptors
scavenger receptors
bind to carbohydrate residues
Signaling receptors induce…
activation of the cell of the innate immune system
Receptors in the cytoplasm
NOD like receptors
RIG-I-Receptors
Membrane bound receptor
Toll Like Receptors (TLR)
TLR Family names after the Toll Gene in
Drosophilia
Structure of TLR
- Transmembrane molecules
- C terminus in cytoplasm (TIR Domain)
- N Terminus in extracellular space ( Pathogen recognition domain)
TIR domain (c terminus)
signaling domain on cytoplasmic end of the molecule and is specialized in binding to signaling proteins and starting signaling cascades
Receptor TLR2
Ligands: Lipoteichoic acid
Microorganism recognized: Gram (+) bacteria
Receptor TLR4 homo-dimer
Ligand: Lipopolysaccharide
Microorganism recognized: Gram negative bacteria
Receptors TLR7 and TLR8, homo-dimers
Ligands: single stranded viral RNAs
Microorganisms recognized: RNA virus
Receptor TLR9
Ligand: Un-methylated (hypo methylated) CpG-rich DNA
Microorganisms recognized: Bacteria
Receptor TLR3
Ligand: Double stranded viral RNA
Microorganism recognized: RNA virus
TLR 5 receptor
Ligands: Flagellin, a protein
Microorganisms recognized: Bacteria
TLR that live in endosomes
Their ligands are nucleic acids, they can only access these when a pathogen has been pretty well degraded beforehand
what TLRs are in the endosomes
TLR3,7,8,9
TLR4 and TLR5
Live on plasma membrane
TLR4 recognizes LPS
TLR5 recognizes Flagellin
TLR2 recognzies
Lipoteichoic acid at the cell surface
What TLR needs help from other molecules to get access to LPS?
TLR4
Molecules that help TLR4 access LPS from pathogens
LBP,CD14,MD2
Why does TLR4 need help from three molecules to access LPS
Because LPS is lipophilic
LBP
Binds and extracts LPS from the bacterial membrane, and takes it to TLR4
MD2 and CD14
make it possible for TLR4 to become activated and recognize LPS
TIR domain of TLR4 binds to
MyD88
The interaction between the TIR domain and the MyD88 recruits
several kinases which turns on a kinase cascade
at the end of the kinase cascade initiated by TIR and MyD88
Transcription factor NFkB becomes activated
When NFkB is actiavted
moves to nucleus and initiates the expressing of several genes. Those genes are involved in inflammation and take the form as secreted cytokines
TLR4 signaling by the TRIF and MyD88 pathway leads to
synthesis and secretion of TNF-alpha and other inflammatory cytokines
PRR of the cytoplasm
NLR (bacterial)
RIGI (viral)
MDA5 (viral)
Inflammasomes (synthesis of biologically active IL1)
NOD Like receptors NLR recognize
bacterial cell wall
inflammasomes recognize
pathogens + intracellular damage or injury
RIGI and MDA5 recognize
Viral nucleic acids
NLRP3 (inflammasome) living in the cytoplasm
- oligomerizes
- activating pro-caspace 1
- becomes active caspace 1
- active caspace 1 can activate IL1B and
- IL1B becomes biologically active
-IL1B binds to receptor - Initiates inflammation
IL1/IL6/TNF-alpha
Acts on:
Liver
Bone marrow endothelium
Hypothalamus
Fat, Muscle
IL1/IL6/TNF-alpha
Liver
Acute phase proteins (CRP + Mannose binding lectin)
IL1/IL6/TNF-alpha
Liver –> activation of
Complement opsonization
IL1/IL6/TNF-alpha
Bone Marrow Endothelium
Neutrophil mobilization
leading to phagocytosis
IL1/IL6/TNF-alpha
Hypothalamus
Increased body temperature,
leading to decreased viral and bacterial replication
IL1/IL6/TNF-alpha
Fat and Muscle
protein and energy mobilization to generate increased body temperature
IL1/IL6/TNF-alpha
Fat and Muscle
protein and energy mobilization to generate increased body temperature
leading to decreased viral and bacterial replication
Dendritic Cell Maturation
Immature state
Tissue resident, resting
Highly endocytic
Low level expression of molecules and cytokines
Poor stimulators of T cells
What turns a dendritic cell from immature to mature?
exposure to inflammatory stimuli, PAMPs
Dendritic Cell Maturation
Mature State
Homes to lymph node
Endocytosis shut down
High level expression of molecules and cytokines
Highly stimulated for T cells
Anti Viral Innate Immune Response
Type I interferon (beta and alphas)
Produced in response to viral infection
Acts in autocrine and paracrine manner to protect from further viral infection
Autocrine
Feeds back on cell that produced signal
Paracrine
Cell that produced it, secreted it, and made it available to other cells in close proximity
Viral Detection and Response activated
Transcription factor IRF - Interferon Response Factor
IRF Transcription Factors
Interferon Response Factors
move to nucleus, once activated, and they active transcription of IFN-alpha and IFN-beta
Virus enters cell, IRF3 turns on
IFN-Beta in the nucleus. Leads to secretion of a cytokine
IRF7 synthesizes
IFN-alpha
Paracrine effect can produce
an anti viral state
upregulation of PKR
inhibition of viral protein synthesis
2,5-oligo A Synthetase
degradation of Viral RNA
Mx GTPases
inhibition of viral gene expression and virion assembly
RIG-I Receptors facilitates two types of responses
Activated IRF3 –> produces type I interferon
activated NFkB –> induced expression of inflammatory cytokines
TLR7 and 3 recognize
Viral RNA, nucleic acids
Induce strong type I interferon responses
TLR3 is the only signaling adapter that doesn’t associate with
MyD88
It associates with TRIF
NK Cells respond to
normal proteins on cell surfaces and abnormal proteins. NK cells have multiple receptors
NK cells
Lymphocytes of the innate immune system
NK cells activity
Killing activity is balanced by activating and inhibitory responses
Macrophages vs NK cells
Macrophage: receptors recognize the cell surface carbohydrates of bacterial cells, not human cells
NK cells: receptors recognize changes at the surface of human cells that are caused by antiviral infections
Type I interferon drives
proliferation of NK cells
Function #1 of NK cells
killing infected or damaged cells
NK cells type of receptors
Inhibitory and Activating receptors
KIRs
Killer cell immunoglobin like receptor
KIRs can be
activating or inhibitory, depending on their cytoplasmic tail
Long tails on KIRs indicate
inhibitory receptor
Short tails on KIRs indicate
short cytoplasmic tails, whig interact with adapter molecules to facilitate signaling
Because activating receptors have a short cytoplasmic tail, they have to interact with
signaling adapting molecule, to exhibit a positive signal
Inhibitory receptors bind to
normal MHC Class I
NK cell mechanism of killing
Formation of NK killing “synapse”
Delivery of toxic molecules in their granules (
- perforin –> pore forming molecule), common with C9 of complement cascade
- granzymes - are delivered through the pore, active an apoptotic cascade, activate caspases
- DNA cleavage, nuclear fragmentation, membrane blebbing
- apoptosis of target cell
Perforin
pore forming molecule (oligomerizes)
granzymes
initiate an apoptotic cascade
Function #2 of NK cells
production of cytokines to activate macrophages
NK cells produce
IFN-gamma (type II interferon)
To stimulate the killing activity of macrophages
chemokines
recruitment and activation of leukocytes
IL1, TNF-alpha, IL6
pro inflammatory cytokines
