Lecture 2 - Innate Immunity Flashcards
Anatomical Barriers
- Skin (epidermis, dermis)
- Mucous membranes (cilia)
- Sebum (oil)
Sebum
- lactic and fatty acids
- lowers skin pH to 3-5
Innate organ protection
1) Urinary tract - acidic pH, long urethra, IgA
2) Vagina - acidic pH, IgA
3) Milk - enzymes
4) Mucous mem, tears, saliva
IgA
Immunoglobulin A
Opsonizes organisms
Defense barriers
1) Anatomical
2) Physiologic
3) Inflammatory
4) Phagocytic
Inflammation
- results from injury
- protective function, but can cause damage
- Can be chronic if infection remains
Signs of Acute Inflammation
1) Tumor - swelling
2) Rubor - redness
3) Calor - heat
4) Dolor - pain
Inflammatory Vasoactive Mediators & Function
- Signal inflammation
- Pain, vasodilation
- prostaglandins (Mast cell)
- histamine (Mast cell)
- bradykinin
Steps of Acute Inflammation
1) Injury, microbe entry
2) Sentinel cells activated
3) Sentinel cells secrete inflammatory mediators
4) Infection red and warm
5) Vasodilation, vessel become permeable to cells, which kill microbes at infected site
Fever
- Cause of strong inflammatory response lead by cytokines TNF, IL-1, IL-6 in macrophages
- Elevated temperature bad for pathogens
PAMPs (and examples)
- Pathogen Associated Molecular Patterns
- Allows discrimination of self and non-self
-Porins, lipoproteins, etc.
PAMP properties
1) Unique to each pathogen class
2) Cannot be concealed since they are necessary for pathogen survival
3) No similarity to host Ags
PRR
- Pattern Recognition Receptor
- How host cells detect pathogens (ex. Mannose Receptor can identify glycan, which is not present on terminal mannose in humans)
Nonclonal Distribution
Receptors (PRR) are identical on every cell — not unique specificity from host cell to cell in innate immunity
TLRs
- Toll-Like Receptor
- Recognize PAMPs by forming pairs with each other, activate inflammation, adaptive response, tissue injury response
- Endosomal (nucleic acids), epidermal (extracellular microbes),
TLR Pairings, Ligands, microorganisms recognized, receptor location
1) TLR1/2 & TLR2/6 – lipopeptides/GPI; bacteria/parasites/fungi; membrane
2) TLR3 – Double-strand viral RNA; Viruses; Endosome
3) TLR4 – Lipopolysaccharide, gram-negative bacteria; membrane
4) TLR5 – flagellin; flagella-bacteria; membrane
5) TLR7, 8 — SingleStrand viral RNA; viruses; endoscopes
6) TLR9; CpG-rich DNA; bacterial virus; endosome
6) TLR10 – unknown
Transcription Factors
- Activated by TLR signals
- Stimulate inflammatory mediator release
- Nuclear Factor-kB
- Interferon Regulator Factor
NF-kB
Nuclear Factor-kB
Promotes cytokine release and adhesion molecule for inflammation response
IRF
Interferon Regulatory Factors
Activate production of antiviral cytokines (IFN-a/b), called Type I Interferons
Signalling Pathways of TLRs
1) TLR1,2,5,6,7,8,9 – activated by respective pathogen, signal MyD88, which produces NFkB or IRF
2) TLR3 — activated by pathogen, signal MyD88, which produces NFkB or IFF
3) TLR 4 – activated by pathogen, signal MyD88 or TRIF, which produces NFkB or IRF
MyD88
- TLR signalling
- an adaptor protein that signals cell to get shit done and make proteins for immune response
TRIF
- TLR signalling
- Adaptor protein that signals cell to get shit done and make proteins for immune response
IRF
- TLR signalling
- Transcription factor
NF-kB
- Transcription factor for protein
- MOST IMPORTANT FOR INFLAMMATION
Extracellular TLR Signaling for NFkB
MyD88 —> IRAK enzymes –> TRAF adaptor protein —> NFkB translocation —> gene activation in the nucleus
TLR4-Dependent Cell Activation
1) TLR4 Complex assembled at macrophage surface
2) MYD88 binds to TLR4, activating IRAK and Phosphorylating TRAF.
3) IKK activated, which inactivates IKB and release of NFkB
4) NFkB activates gene transcription of cytokines
TLR Deficiencies (and two types)
- Results in immune cell not able to kill microbe — recurrent infections in patients and infection susceptibility
1) MyD88 deficiency
2) IRAK-4 deficiency
NLRs
- NOD-Like Receptors (NLRP3 most important)
- Present in inflammasomes, activated by PAMPs
- Scaffolding Proteins that aid activation of NFkB and MAPK pathways
Inflammasome
- Protein complex triggered by PAMPs
- Activate Protease caspase-1, which processes active IL-1B and IL-18 that comes from the nucleus of the immune cell, which drives inflammation
IL-1B & IL-18
Important interleukins that are activated by caspase-1 and are very potent cytokines that drive inflammation
NLRP3 Inflammasome & Gout
- IL-1B is key Gout cytokine that promotes acute inflammatory response in the gout joint and accumulation of monosodium urate
- Anti-IL-1 therapy is good treatment
DAMPs
- Damage-Associated Molecular Patterns
- Released from damaged/dying cells (i.e. NECROSIS) —> NOT APOPTOSIS
- Induce non-infection inflammatory response via NF-kB
- Activated by PRR interaction and Macrophage signaling for inflammation response
DAMP examples (relevant TLR and NLR)
1) HMGB1 - necrotic cells (TLR2/TLR3)
2) Uric Acid (NLRP3)
3) Heat Shock Proteins - cytoplasmic proteins (TLR2/TLR4)
DAMPs In Autoimmune Diseases
- Impact/promote adaptive immunity which can backfire:
- multiple sclerosis, Type 1 Diabetes, lupus, Rheumatoid Arthritis
Neutrophils vs Macrophages (origin, lifespan, cytokine production)
Neutrophils
-Marrow, 1-2 days, low
Macrophages
-Marrows, days (inflammatory) to years (tissue), very high
PRR-Triggered Responses in Phagocytes (explain migration)
1) Killing Microbes
2) Migration
Macrophage Functions
1) Respond to Danger Signals (PAMP & DAMP)
2) Regulate Extravasation of blood into tissues
3) Phagocytosis
4) Tissue Repair
5) Inflammatory
6) Antigen Presentation
Inflammatory Mediators examples
1) Cytokines
2) Reactive oxygen intermediates
3) Nitric oxide
4) Prostaglandins
5) Defensins
Mast Cells
- Important for allergic rxns
- Has PAMP/DAMP receptors
- Live for long time
- Secrete inflammatory, anti-inflammatory, immunosuppressive products
Strategic location off Mast Cells
- Near skin and exposed sites cause sentinel cells
- Near blood vessels to regulate vascular permeability
- Modulate local cell responses through chemical mediators
Mast Cell Activators
Chemical
-PAMPs
-IgE (Abs)
-Ags
-Cytokines
-Chemokines
Physical
-Temperature
-PressureMast Cell Effector Molecules (release time)
Seconds
-Histamine, Proteases, TNF
Minutes (De novo mediator production)
-Prostaglandins, Leukotrienes
Hours (De novo mediator production)
-TNF, IL-4
Granules replenished after days
Cytokines
- Peptides secreted to mediate:
- Inflammation, Immunity, hematopoiesis
- Pro-inflammatory and anti-inflammatory
- Endocrine (long distance), paracrine or autocrine
- Function dependent on cell it binds to
Chemokines
Chemoattractants that help move immune cells
IL-10
- Anti-inflammatory cytokine
- Macrophages principle source
- Inhibition of cytokines and chemokines, target dendritic cels and macrophages
TGF-B
- Anti-inflammatory cytokine
- Macrophages principle source
- Target T-cell, stop inflammation
IL-1B (Local & Systemic)
Local
-Activates: lymphocytes, vascular endothelium permeability
Systemic
-Fever, IL-6 production
TNF-a
Local
-Increase vascular permeability to let IgA into tissues
Systemic
-Fever, shock, metabolite mobilization
IL-6
Local
-Lymphocyte activation, antibodies
Systemic
-Fever, acute phase protein production
IL-8
Local Only
-Recruits neutrophils, basophils, Tcells to infection
IL-12
Local Only
-Activates NK cells, induces transition of CD4 TCells into THelper cells
Sickness Behavior Syndrome
- From systemic release of TNF-a, IL-1, IL-6
- Lethargy, depression, anorexia, fever, cognitive impairment
Complement System
- Activation results in the production of polypeptide fragments that are essential for inflammation and immunity — enhances ability of body to kill microbes
- 30 proteins make it up
- All make C3b fragment
- Forms MACs
MACs
- Membrane attack complex
- Create holes in membranes and kills pathogens via osmotic shock
- C5b triggers self-assembly of MAC
IL-6, IL-1 and TNF-a
Act on hepatocytes for increase in APR proteins — major signalers for Acute Phase Protein Response
Acute Phase Protein (APP) (Types and Roles)
1) C-reactive —- opsonizes, fixes complement system
2) Mannose binding —- opsonizes, fixes complement system
3) Acid glycoprotein - transporter
4) Serum Amyloid — Amyloid component precursor
APP serum concentrations
- Low concentration levels in healthy people
- After inflammation, APP levels high, peaking 24-48 hours after onset
- ALLOWS FOR DETECTION OF INFLAMMATION!!!
Innate immune cell movement to tissues
- Neutrophils and monocytes enter through:
1) Post-capillary venules - all
2) Capillaries - liver, lungs, kidney
Chemotaxis
-Substance released by bacteria or damaged cell that stimulates the movement of neutrophils to that area
What is hemodynamic shear?
Friction force acting on the blood vessel as a result of blood flow
(Venules have low hemodynamic shear, which is why they are good for migration)
What are the steps for neutrophil/monocyte migration?
1) Endothelial activation – TNF & IL-1 activate endothelial cells, which express P-, E-selectin
2) Tethering – Neutrophils bind to selectin with their carbs (PSGL-1; ESL-1)
3) Rolling – Blood flow disrupts carb-selectin bond, which reattaches downstream (this causes rolling)
4) Binding – Integrin affinity on leukocytes increased by endothelial cytokines binding to leukocyte chemokine receptor, arresting the cell
5) Tissue Entry – leukocyte moves through the cell wall and into the tissues
6) Migration/Chemotaxis — IL-8 directs neutrophils to inflammation site
What are LFA-1, VLA-4?
- Late Function Antigen 1 & Very Late Antigen 4
- Neutrophil integrin proteins
- Bind to ICAM-1 and VCAM-1 on endothelial cells, stopping neutrophil roll
- Chemokine receptor increases intern affinity for ligands (Extended conformation)
What are ICAM-1, VCAM-1 and PSGL-1?
- Intercellular Adhesion Molecule 1 & Vascular Cell Adhesion Molecule 1
- Ligands that LFA-1 and VLA-4 bind to
- Present on endothelium cells
PSGL-1 is the main endothelial adhesion molecule for MONOCYTE migration for P-Selectin
What are the chemokines used in neutrophil and monocyte migration?
- IL-8, which lines endothelium and attaches to IL-8 receptor on neutrophil
- MCP-1 — for monocytes
Neutrophil rolling is……
….selectin dependent
What is MCP-1?
- Monocyte chemoattractant protein 1
- Helps arrest MONOCYTES to endothelium during migration
- MOST IMPORTANT FOR MONOCYTES
How are monocyte activated to become macrophages by the Classical Pathway?
- Activated by
1) microbial ligand binding to TLR
2) IFN-gamma (cytokines)
What is the function of Classically Activated Macrophages?
1) Microbe kiling
2) Inflammation activation
How are monocyte activated to become macrophages by the Alternative Pathway?
Activated by:
1) IL-13 and IL-4
What us the function of Alternatively Activated Macrophages?
- Anti-inflammatory
- Tissues repair
- Fibrosis
Immunomodulation
Process that modulates the immune response to a desired level (pro-inflammatory and anti-inflammatory)
What is the Role of PRR in Phagocytosis?
-They bind to the microbes, triggering a signal to the cell to ingest the microbe
What ROSs kill microbes and how are they created?
- Radical Oxidative Speciaes
- OH (Hydroxyl radical); OCl (hypochlorite); H2O2 (peroxide)
1) Respiratory Burst
What are the steps of the Respiratory Burst?
1) O2 -> O2- (superoxide) via NADPH oxidase
2) O2- —> H2O2 (peroxide) (via Superoxide dismutase)
3) H2O2 —-> OCl (hypochlorite m– MOST ANTIMOCRIBIAL) + OH+ (hydroxyl radical) via myeloperoxidase
What mediates Innate Immune Response against viruses and what do they do?
1) Type I Interferons (alpha/beta) – block viral replication
2) Natural Killer (NK) Cells – kill infected cells
Why are Type I Interferons important and how do they achieve their function?
Regulators of the killing of virally-infected cells
- Released by dendritic cells -> bind to infected cell receptor -> signal transduction to:
1) Inhibit protein syntheis
2) Degrade RNA
3) Inhibit gene expression
What are the (basic) steps of killing for NK cells?
1) Recognize ligand on infected/stressed cells
2) Kill infected cells or stressed host cells
3) Eliminate infection reservoirs (kill host cells and release pathogens for host phagocytosis)
How do NK cells stimulate macrophages?
-By secreting IFN-gamma (Type II Interferon), which is the most powerful macrophage activator to kill microbes
What is the activation mechanism in NK cells?
- Killer cell immunoglobulin (Ig)-like receptors (KIRs)
- Stress molecules on cell recognized -> KIRs activate protein tyrosine kinases (PTKs)
What is the inhibitory mechanism in NK cells?
-KIR receptors recognize MHC-I and activate “protein tyrosine phosphotases” (PTP) that inhibit signal.
Key: Insufficient binding of MHC-I by KIRs will not override kill signal
How do NK cells kill infected cells?
1) PERFORINS are released by NKs, make hole in infected cell (think “perforate”)
2) Granzymes enter infected host, initiate apoptosis
3) Infected cell dies
4) Macrophage eats dying cell and detritus
Explain some mechanisms for bacterial escape from innate immune system defense
1) Polysaccharide inhibits phagocytosis
2) Breakdown of ROS in phagolysosomes
3) Inhibition of C3 and C5 convertase
How does the innate immune system link to the adaptive immune system and what does it lead to?
- Two signal activation:
1) Signal 1 – microbe binds./recognized by lymphocyte
2) Signal 2 – Molecules from APCs (costimulatory molecules)
Leads to…..Lymphocyte proliferation!!!
INNATE indirectly controls Ab-mediated response of adaptive immunity
Steps for Innate-Adaptive linkage
1) PRR recognizes pathogen
2) PRR activates and APC, allowing it to mature
3) APC presents antigen to you T Cell
4) Cytokines secreted, assist in T cell development
