Innate Immunity Flashcards
Opsonization
Coating a microbe with molecules that can be recognized by receptors on phagocytes
Ex. IgG expressed on microbe, IgG binds to receptors on phagocyte, crosslinks
Phagocytosis (4 steps)
- Fc receptors on phagocyte bind to opsonized microbes
- Fc receptor signals activate phagocyte
- Phagocytosis of microbe
- Killing of ingested microbe
Role of immune system (4)
- Defense against infection (vaccinations boost immune defenses)
- Defense against tumors (immunotherapy for cancer)
- Injure cells; pathologic inflammatory response (cause of allergic, autoimmune, inflammatory diseases)
- Recognizes and responds to tissue grafts and newly introduced proteins (barriers to gene therapy and transplantation)
Principles of Innate Immunity
Inflammation or antiviral defense
- Present in healthy individuals at birth
- Receptors are encoded in germline
- Restricted response without memory**
- Immediate
- Physical and chemical barriers (1st line of defense)
- Enhances adaptive immune responses
- Response similar to repeat encounters with an infectious organism
- Able to recognize and respond to invariable (nonchanging) structures
- Does not normally react against host
Innate Immunity Defense (at site of microbial entry)
GI tract, epithelium, resp. tract
Physical barrier, antimicrobial molecules, lymphoid cells
Innate Immunity Defense (at tissues where microbes breach)
Macrophages, dendritic cells, mast cells (secrete cytokines)
Initiation of inflammation
Phagocytes destroy microbes and then eliminate damaged cells
Innate Immunity Defense (in blood)
Plasma proteins complement microbial destruction
Innate Immunity Defense (for Viruses)
Induce production of interferons from infected cells to inhibit infection of other cells
Through the production of Natural Killer cells (that kill)
Adaptive Immunity
- Specific or acquired
- Memory responses through somatic rearrangement of gene segments during lymphocyte development leading to clonal expansion of B and T lymphocytes
- Immune response:
Expansion and differentiation of lymphocytes
Adapts based on exposures and vaccines - Develops later in life
- Lymphocytes (receptors) and immunoglobulins (antibodies)
Specificity (Innate vs Adaptive)
Innate: Structures shared by classes of microbes (PAMPs) or damaged cells (DAMPs)
Identical TLRs recognize different microbes
Adaptive: For structural detail of microbial molecules (antigens); may also recognize nonmicrobial antigens
Distinct antibodies recognize different microbes
Receptors (Innate vs. Adaptive)
Innate: Encoded in the germline; limited diversity
NOD-like receptors (cytosolic), mannose receptors, Toll-like receptors
Nonclonal (identical receptors on all cells of the same lineage)
Adaptive: From somatic recombination of gene segments; greater diversity
Clonal (clones of lymphocytes with distinct specificities express different receptors)
Microbial Recognition (Innate vs. Adaptive) and their interplay
Innate:
Recognize structures shared by classes of microbes that aren’t present on host cells
Enhanced function through adaptive immune system
Adaptive:
Lymphocytes express receptors (antibodies) on their cell surface that recognize specific antigens
–> Molecules present on microbe surface
–> Non-infectious substances that are involved in a microbial infection
Utilizes cells of innate immunity (phagocytes) to eliminate microbes
Antibody binds to microbe, which activates phagocytes (innate) to ingest and destroy the molecule
PAMPs
Pathogen-associated Molecular Pattern
Recognized by the PRR (innate)
Microbial molecules, shared by microbes of the same type
Not on normal host cells
Stimulate innate immune responses
Essential for survival/infectivity
DAMPs
Damage-associated Molecular Pattern
Recognized by the PRR (innate)
Released from damaged or necrotic host cells
Present in injury (infarction) or infection
Toll-Like Receptors (TLRs) (innate)
Specific for microbial components
Extracellular: lipids, proteins, polysaccharides on cell surface of microbe
Intracellular: nucleic acids of ingested microbes
Activate TFs to stimulate production of cytokines, enzymes, etc.
Ex. Nuclear factor KB (NFKB) promotes items involved in fighting infection
Defect in TLR signaling (recurrent or severe infection)
TLR Signaling Cascade (innate)
- TLR binds bacterial or viral molecule
- Recruits proteins to activate transcription
- NF-kB
- Increases production of cytokines, adhesion molecules, and costimulators
- Acute inflammation, stimulation of adaptive immunity
OR
- Interferon Regulatory Factors (IRFs)
- Increases production of type 1 Interferons (IFN a, B)
- Antiviral state (blocks viral replication in host cells)
NOD-like Receptors (innate)
Family of cytosolic receptors that sense DAMPs and PAMPs in cytoplasm that contain: Central NOD (nucleotide oligomerization domain) Different N-terminal domains
NOD1 and NOD2
Contain N-terminal (Caspase Related Domains)
Bacterial peptidoglycans in the cell wall
Activated NF-kB
NLRP-3
Recognizes microbial products, substances associated with damage, and endogenous substances in large quantities (crystals)
Enhances production of IL-1bB (inflammation, fever)
Inflammasome
- NLRP-3 oligomerizes with inactive caspase-1 inflammasome
- Activated caspase-1 cleaves IL-1B precursor (coming from nucleus after innate signals enhanced production of pro-IL1B)
- Activated IL-1B generates fever
Inflammatory dysregulation:
Gout: urate crystal deposit
Autoinflammatory syndromes
Components of Innate Immunity (10)
- Epithelial barrier
- Phagocytes: neutrophils and monocytes/macrophages
- Dendritic cells
- Mast cells
- Innate lymphoid cells
- Natural Killer cells
- Lymphocytes with limited diversity
- Complement
- Plasma proteins
- Cytokines
Epithelial Barrier
- Mechanical barrier of tightly adherent cells
- Produce mucous
- Chemical barrier of peptide antibiotics (defensins and cathelicidins)
- Intraepithelial lymphocytes: limited diversity, function is not well known
Barriers to infection and presence of microbial killers (local antibiotics and intraepithelial lymphocytes)
How do leukocytes get to where they need to go? (5)
- Rolling
- Guided to epithelial barrier by selectins which slow the cell down
- Integrins activated by chemokines bind to the cell via ligands to the epithelium
- Stable adhesion
- Migration through endothelium
Integrins are what directly cause binding for diapedesis
Once inside the tissue, chemokines direct to area of infection
Cytokines at infected area promote more recruitment to area of infection
Neutrophils (phagocytes)
[Polymorphonuclear leukocytes (PNMs)]
- Most abundant leukocyte in the blood
- Increase rapidly during infection (cytokine simulation
- First cell to respond to infections (bacterial and fungal)
- Dominant cell of inflammation
- Phagocytose microbes in the blood and tissues and destroy them
- Recruited to tissues to remove debris
- Live for only a few hours in tissues, dead ones form pus
Band neutrophil
Immature neutrophils
Can be released when they’re immature because the stimulation is so intense
Indicative of an overwhelming infection
Oxidative (Respiratory) Burst and ROS toxicity to microbes
- Microbe is recognized by PRRs and phagocytosis occurs
- Membrane closes around microbe, forming a phagosome
- Phagosome fuses with lysosome forming a phagolysosome
- Phagocyte oxidase converts molecular oxygen into ROS
- ROSs are toxic to microbes and work with inducible nitric oxide synthase (iNOS) and lysosomal proteases to destroy microbes
Monocytes/macrophages (phagocytes)
- Monocytes differentiate into macrophages in tissues
Brain: Microglial cells
Liver: Kupffer cells
Lungs: Alveolar macrophages - Found in all connective tissues and organs
- Survive very long in tissues
- Ingest microbes in blood and tissues
- Clear dead tissues
- Initiate tissue repair
Macrophages
- Cytokines regulate and induce inflammation
- Phagocytose microbes because of recognition on cell surface receptors
- Activated by PRRs (TLRs and NLRs)
- Clear dead tissues
- Initiate repair process
- Some phagocytic receptors activate killing
- Respond to cytokines
Macrophage activation (classical vs. alternative)
Classical:
- Monocyte (with TLR ligands, cytokine IFN-g) form classically activated macrophage (M1)
- Releases ROS, NO, lysosomal enzymes to destroy microbes
- Releases IL-1, IL-12, IL-23, chemokines to induce inflammation
Alternative:
- Monocyte (with cytokines IL-4 and IL-13) form alternatively activated macrophage (M2)
- Releases IL-10, TGF-B
- Aids tissue repair and termination of inflammation
Dendritic Cells
Antigen presenting cells
Produce cytokines to initiate inflammation and stimulate adaptive immune responses
Bridges innate and adaptive immunity
- Antigen captured by DC (immature)
- DC activated
- DC travels through lymphatic vessel to naive T cell
- Mature DC presents antigen to T cell
DC have lots of arms because its purpose is to tag onto things
Mast Cells
Abundant cytoplasmic and vasoactive granules
Skin and mucosal epithelium
More inflammatory than killing cell
- Activated by:
>Microbial products binding to TLRs (innate immunity)
>Antibody-dependent (allergic reactions) - Vasoactive amines (histamines and tryptase)
>Increase capillary permeability
>Kill bacteria and inactivate microbial toxins - Synthesize and secrete lipid mediators (prostaglandins) and cytokines (TNF)
>Stimulate inflammation
Natural Killer (NK) Cells - CD16/56
- Identify infected and stressed cells and kill them
>Empty cytoplasmic granules into extracellular space near the infected cell
>Granules enter the cell and activate enzymes to induce apoptosis - Intracellular microbial infections
>Like tumors or viral infections - Secrete IFN-g (macrophage activation)
- Activated by cytokines from macrophages and dendritic cells
>IL-15: development and maturation of NK cells
>IL-12 and type I IFNs: enhance NK cell killing function
Activation of NK cells
- To eliminate cells infected with intracellular microbes
>Antibody-dependent cellular cytotoxicity (ADCC)
»CD16 cell surface marker specific for IgG bound to cells
>Immunoreceptor tyrosine-based activation motifs (ITAMs) in their cytoplasmic tails
»ITAMs become phosphorylated on tyrosine residues and recognize their activating ligands, promoting activation of cytosolic protein tyrosine kinases and activate other substrates involved in downstream signaling pathways causing cytotoxic granule exocytosis and production of IFN-g - Eliminate injured cells and tumor cells with stress from DNA damage and malignant transformation
Inhibition of NK cells
To block signaling by receptor activation specific for “self” MHC I molecules to protect healthy cells
Inhibitor receptors (on NK cell):
>Contain immunoreceptor tyrosine-based inhibitor motifs (ITIMs) that become phosphorylated on tyrosine residues when receptors bind to MHC I (on normal cell)
>Then bind and promote activation of cytosolic protein tyrosine phosphatases which remove the phosphate groups from the tyrosine residues of signaling molecules, counteracting ITAMs, blocking NK cell activation
Killer cell immunoglobulin-like receptors (KIRs)
CD94 and lectin subunit NKG2
NK Cell ADCC
Antibody-dependent cellular cytotoxicity
Antibodies (IgG) recognize viral glycoproteins expressed on the surface of cells infected with the enveloped viruses
Therapeutic intervention in treating tumor cells
- IgG binds to surface antigens on antibody-coated cell
- Antibodies bind to CD16 on NK cell
- Killing of antibody-coated cell
Complement System (Alternative, Classical, Lectin; C3a, C3b, C5a, C6-9)
- Initiation of complement activation:
Alternative (innate)
Triggered when activated complement proteins on microbial surfaces are uncontrolled due to lack of regulatory proteins
Classical (adaptive)
Triggered antibodies bound to microbes/antigens
Lectin (innate)
Mannose binding lectin (MBL) binds to terminal residues on microbial cell surface glycoproteins
All release complements that aid in next steps
- Early step:
C3 > [help of complements from pathway] > C3b > C3a breaks off of C3b
C3a: Inflammation
C3b: OPSONIZATION and PHAGOCYTOSIS (C3b is deposited on microbe)
C5 > [help of C3b-microbe complex] > C5b > C5a breaks off of C5b
C5a: INFLAMMATION
C6-9: LYSIS of microbe (form membrane attack complex MAC)
Membrane Attack Complex (Complement System)
C5 convertase causes proteolysis of C5 > C5b
C5b binds with C6, C7, C8, and C9s
Forms pore in cell membrane
Allows for influx of water and ions
Cell death
C6-9: Lysis of microbe
Activated by C3b
Acute Phase Response
When plasma proteins increase rapidly with infection
Collectins
Plasma proteins (innate)
- Mannose binding lectin (MBL):
Recognizes microbial carbohydrates, coating them for phagocytosis
Activation of complement by lectin pathway - Surfactant:
Soap like substance in the lung protective from infectious microbes
C-reactive protein (CRP)
Plasma proteins (innate)
Binds phosphorylcholine on microbes, opsonizes them for phagocytosis by macrophages (CRP receptor)
Activates classical complement pathway proteins
Produced as part of the acute phase response and in the case of Gram+ bacteria, a common means of stimulation would be via TLR-2 on macrophages
Cytokines (innate)
Interleukins
- Soluble proteins that cause cell signaling to generate immune and inflammatory reactions - stimulated by infection
- Communication between cells
- Produced by activated and act on leukocytes
- Innate immunity: mast cells, dendritic cells, macrophages
- Adaptive immunity: helper T lymphocytes
TNFs, IL-1, Chemokines (cytokines)
Recruitment of neutrophils and monocytes
TNF, IL-1 (cytokines)
Produce fever by acting on the hypothalamus
IL-6 (cytokines)
Acute phase response protein synthesis from the liver: CRP and fibrinogen
TNF at high concentration (cytokines)
Thrombus formation
Hypotension: reduced myocardial contractility and vascular dilation and leakage
High TNF, IL-12 from dendritic cells and macrophages (in response to LPS and microbial molecules) - (cytokines)
Septic shock: hypotension, disseminated intravascular coagulation, metabolic disturbances
Type 1 Interferon
Important in viral infections (creates antiviral state)
Type 1 interferon binds to the virus >Blocking enzymes necessary for viral replication >>Inhibiting protein synthesis >>Degrading viral RNA >>Inhibiting viral gene expression
Tumor Necrosis Factor (TNF)
Cytokine
Cell source:
Macrophages, T cells, Mast cells
Cell target/bio effects: Endothelial cells: activation (inflammation, coagulation) Liver: synthesis of acute-phase proteins Hypothalamus: fever Neutrophils: activation Muscle, fat: catabolism (cachexia) Many cells: apoptosis
Increases the expression of MHCII molecules on APC
Interleukin-1 (IL-1)
Cytokine
Cell source:
Macrophages, dendritic cells, endothelial, epithelial, mast cells
Cell target/bio effects: Endothelial cells: activation Hypothalamus: fever Liver: synthesis of acute-phase proteins T cells: Th17 differentiation
Chemokines
Cytokine
Cell source:
Macrophages, endothelial cells, T cells, dendritic cells, fibroblasts, platelets
Cell target/bio effects:
Leukocytes: increase integrin affinity, chemotaxis, activation
Interleukin-12 (IL-12)
Cytokine
Cell source:
Dendritic cells, macrophages
Cell target/bio effects:
NK cells and T cells: IFN-g production, increased cytotoxic activity
T cells: Th1 differentiation
Interferon-g (IFN-g)
Cytokine
Cell source:
NK cells, T lymphocytes
Cell target/bio effects:
Activation of macrophages (Th1 response)
Stimulation of some antibody responses
Increased MHCI, MHCII expression
Only member of Type 2 IFN
Essential for Innate and adaptive immunity
Type 1 IFNs (IFN-a, IFN-b)
Cytokine
Cell source:
IFN-a: Dendritic cells, macrophages
IFN-B: Fibroblasts
Leukocytes
Cell target/bio effects:
All cells: antiviral state, increased MHCI expression
NK cells: activation
Binds to INFAR1/INFAR2
IFNa only: increase MHCII expression
Interleukin-10 (IL-10)
Cytokine
Cell source:
Macrophages, dendritic cells, T cells
Cell target/bio effects: Macrophages, dendritic: inhibition of cytokine and chemokine production, REDUCED expression of costimulators and class II MHC
Calming effect
Reduces immune activation
(Can switch off T cells)
Interleukin-6 (IL-6)
Cytokine
Cell source:
Macrophages (in response to PAMPs), endothelial cells, T cells
Cell target/bio effects:
Liver: synthesis of acute-phase proteins
B cells: proliferation of antibody producing cells
Mediator of fever
Crosses BBB and initiates synthesis of PGE2 in hypothalamus
Interleukin-15 (IL-15)
Cytokine
Cell source:
Macrophages, others
Cell target/bio effects:
NK cells: proliferation
T cells: proliferation
Interleukin-18 (IL-18)
Cytokine
Cell source:
Macrophages
Cell target/bio effects:
NK and T cells: IFN-g synthesis
TGF-B
Cytokine
Cell source:
Many cells
Cell target/bio effects:
Inhibition of inflammation
T cells: differentiation of Th17, regulatory cells
Can switch off T cells
Chronic granulomatous disease
Functional Deficiencies:
Defective production of reactive oxygen intermediates in phagocytes
Mechanisms of Defect:
Mutations in genes encoding phagocyte oxidase enzyme, mainly b558
Leukocyte adhesion deficiency-1
Functional Deficiencies:
Absent or deficient expression of B2 integrins causing defective leukocyte adhesion-dependent functions
Mechanisms of Defect:
Mutations in gene encoding the B chain (CD18) of B2 integrins
Leukocyte adhesion deficiency-2
Functional Deficiencies:
Absent or deficient expression of leukocyte ligands for E and P selectins, causing failure of leukocyte migration into the tissues
Mechanisms of Defect:
Mutation in the gene encoding a protein required for synthesis of the sialyl-Lewis X component of E and P selectin ligands
Complement C3 Deficiency
Functional Deficiencies:
Defect in complement cascade activation
Mechanisms of Defect:
Mutation in the C3 gene
Complement C2, C4 deficiency
Functional Deficiencies:
Deficient activation of classical pathway of complement leading to failure to clear immune complexes and development of lupus-like disease
Mechanisms of Defect:
Mutations in C2 or C4 gene
Chediak-Higashi Syndrome
Functional Deficiencies:
Defective lysosomal function in neutrophils, macrophages, and dendritic cells, and defective granule function in natural killer cells
Mechanisms of Defect:
Mutation in a gene encoding a lysosomal trafficking regulatory protein
Herpes Simplex Virus 1 (HSV-1) encephalitis
Functional Deficiencies:
Defective antiviral immunity in the CNS
Mechanisms of Defect:
Mutations in the TLR3 gene
Recurrent pyogenic bacterial infections
Functional Deficiencies:
Defective innate immune response to pyogenic bacteria
Mechanisms of Defect:
Mutations in MyD88 gene
Discrimination against self-antigens (Innate and Adaptive)
Prevent cell death and autoimmunity
Innate:
Receptors specific for PAMPs and DAMPs, not healthy substances
PRRs that recognize NAs (on normal cells) but located in cellular components where healthy cells are not accessible
Adaptive:
Lymphocytes that recognize self undergo apoptosis or are inactivated when they encounter self antigens
IL-8
Chemotactic for neutrophils
TNF-a
Improves cell surface molecules that improve adhesion of
Derived from monocytes and is a potent pyrogen
Causes fever directly or through IL-1; induces cachexia
Superantigens (produced by, causes)
Exotoxins that cross-link TCR to Class II MHC
Instead of activating 1 in 10,000 T cells, as many as 1 in 5 are stimulated
Leads to massive IFN-g and IL-2 production
Acts on vascular endothelium to cause capillary leakage
Results in hypotension, shock, and death
Produced primarily by S. aureus and S. pyogenes
Causes:
Toxic shock syndrome
S. aureus causes:
- Toxic shock syndrome
2. Sometimes food intoxication
Treatment for TSS
1. Manage infection Blood culture Antibiotics asap Catheter replacement Surgery? 2. Manage shock Oxygen, IV fluids Breathing machines, kidney dialysis
Currently no drugs to target immune response
Drugs under consideration for TSS
- Anti-inflammatory
- Drugs/immunotherapy targeting cytokines
- Anticoagulants
- Plasma exchange
- Vitamin/corticosteroids
Vitamin C may improve blood flow to organs?
Good results - NSAIDS
Help with blood flow
Inhibit caspases
Accelerate PhenoTest BC
Identification and antibiotic susceptibility of organisms for bloodstream infections
Identification in 90 min
Antibiotic susceptibility in 7 hours
TSS
Sudden fever followed by headache, sore throat, diffuse red rash, skin desquamation
Shock within 48 hours
6,000/year
5/65% fatality with and without treatment
TLR-4
Binds to LPS
