L3 - Innate immunity 2: The induced response Flashcards
Innate immune cells
- Neutrophils
- Macrophages
- Dendritic cells
- Natural killer cells
Function of neutrophils
- Phagocytosis
- Reactive oxygen and nitrogen species
- Antimicrobial peptides
- NETs - neutrophil extracellular traps
Function of macrophages
- Phagocytosis
- Inflammatory mediators
- Antigen presentation
- Reactive oxygen and nitrogen species
- Cytokines
- Complement proteins
Function of dendritic cells
- Antigen presentation
- Costimulatory signals
- Reactive oxygen species
- Interferon
- Cytokines
Function of natural killer cells
- Lysis of viral-infected cells
- Interferon
- Macrophage activation
How does phagocyte recruitment occur
1) Rolling
2) Activation
3) Arrest/adhesion
4) Transendothelial migration
Effect of cytokines on blood vessels
- Cytokines dilate local blood vessels
What do chemokines attract to infection sites
- Chemokines attract monocytes and neutrophils to the infection
- Cell adhesion molecules (ICAM-1 and ICAM-2) are upregulated on the endothelium which bind to integrins (family of adhesion molecules) on the leukocytes
What is phagocytosis performed by
- Performed by neutrophils and macrophages
- Phagocytosis is the capture and digestion of foreign particles
Examples of opsonins
- Complement components (C3b)
- Collectins (mannose-binding lectin) antibodies
Examples of phagocytic receptors
- Complement receptors
- Fc receptors
- Mannose receptor
- Scavenger receptors
Summary of receptor mediated phagocytosis
- Macrophage receptors that recognise components of microbial surfaces
- Microorganisms are bound by phagocytic receptors on the macrophage surface
- Microorganisms are internalised by receptor-mediated endocytosis
- Fusion of the endosome with a lysosome forms a phagolysosome in which microorganisms are degraded
Antimicrobial mechanisms of phagocytes
- Acidification
- Toxic oxygen-derived products
- Toxic nitrogen oxides
- Antimicrobial peptides
- Enzymes
- Competitors
Effect of acidification
- pH - 3.5-4.0, bacteriostatic or bactericidal
Examples of oxygen-derived products
- Superoxide O2-, hydrogen peroxide H2O2, singlet oxygen 1O2, hydroxyl radical OH, hypohalite OCL-
Examples of antimicrobial peptides produced by macrophages
- Cathelicidin, macrophage elastase-derived peptide
Examples of antimicrobial peptides produced by neutrophils
- alpha-defensins (HNP1-4), beta-defensin HBD4, cathelicidin, azurocidin, bacterial permeability inducing protein(BPI), lactoferrin
Effects of lysozymes
- Digests cell walls of some gram-positive bacteria
- Acid hydrolases (eg. elastase and other proteases): break down ingested microbes
Examples of competitors
- Lactoferrin(sequesters Fe2+)
- vitamin B12 binding protein
What are neutrophill extracellular traps (NETs)
- When activated, some neutrophils undergo a special form of cell death termed ‘NETosis’
- During NETosis, nuclear chromatin is released from cells trapping microorganisms thus aiding phagocytosis
What are pattern recognition receptors (PRRs)
- Receptors able to recognise conserved structures
- They recognise patterns termed: Pathogen-associated molecular patterns (PAMPs)
Examples of pattern recognition receptors
- Toll-like receptors (TLRs)
- NOD-like receptors (NLRs)
- Rig-I like receptors (RLRs)
- Cytosolic DNA sensors (CDS)
What are PAMPs
- Microbes evolve rapidly, so innate immunity must focus on highly conserved and essential components of microbes (cell wall structures; nucleic acids)
What are DAMPs
- Damage associated molecular patterns, molecules released from necrotic cells
Effect of mutations on microbe survival
- Random mutations that occur in microbes play a significant role in their ability to survive and adapt due to the speed at which they replicate
Importance of drosophila toll receptor
- Mutagenesis work on drosophila revealed two members of the Toll family, dToll and 18-wheeler
- Important for development
- Important for immunity to the fungal and bacterial infections
- Mammalian equivalent are the Toll-like receptors
Toll-like receptor structure
Extracellular: LRR domain - site of pathogen binding
Cytosolic side: TIR-domain - conserved stretch of - 200 amino acids
What do convex surfaces of TLRs contain
- The convex surfaces of TLR-1 and TLR-2 have binding sites for lipid side chains of triacyl lipopeptides
What induces dimerisation between TLRs
- Binding of each TLR to the same lipopeptide induces dimerisation, bringing their cytoplasmic TLR domains into close proximity
TLRs located on the cell surface
- TLRs 1, 2, 4, 5, 6
Endosomal TLRs
- TLRs 3, 7, 8, 9, 10
Bacterial products recognised by TLRs
- Lipopolysaccharude (LPS)
- Flagellin
- Lipoteichoic acid
- HSP70
- Fibrinogen
- Fibronectin
Viral products recognised by TLRs
- dsRNA
- ssRNA
- DNA
What does TLR signalling induce
- TLR signalling induces genes that function in host defense
- Pro-inflammatory cytokines
- Chemokines
- MHC and co-stimulatory molecules
- Antimicrobial peptides and complement components
What is MyD88
- The MyD88 protein acts as an adapter, connecting proteins that receive signals from outside the cell to the proteins that relay signals inside the cell
- In particular, MyD88 transfers signals from certain proteins called Toll-like receptors and interleukin-1 (IL-1) receptors, which are important for an early immune response to foreign invaders such as bacteria
What does the MyD88 adaptor protein stimulate
- In response to signals from these receptors, the MyD88 adapter protein stimulates signalling molecules that turn on a group of interacting proteins known as nuclear factor-kappa-B.
- Nuclear factor-kappa-B regulates the activity of multiple genes, including genes that control the body’s immune responses and inflammatory reactions. It also protects cells from certain signals that would otherwise cause them to self-destruct (undergo apoptosis).
Link between somatic mutations in MYD88 and CXCR4and waldenstrom’s macroglobulinemia
- Somatic mutations in MYD88 and CXCR4 are determinants of clinical presentation and survival
What is waldenstrom macroglobulinemia
- Is a rare type of non-hodgkin lymphoma
- B cells make large amounts of IgM that can cause excess bleeding, vision problems and headaches
- Lymphoma cells proliferating in the bone marrow can cause anaemia, neutropenia and thrombocytopenia
Link between TLR3 and herpes
- TLR3 deficiency in patients with herpes simplex encephalitis
- Defects in other signalling molecules involved in the TLR3 signalling pathway have also been associated with HSE
What is herpes simplex encephalitis
- Inflammation of the brain due to infection with herpes simplex virus (HSV-1)
What is HSV-1
- HSV-1 is a dsDNA virus, but during viral replication it produces dsRNA
HIV - TLR
TLR8
Sepsis - TLR
TLR2 and 4
Tuberculosis - TLRs
TLR2 and 4
Systemic lupus erythamatosus - TLRs
TLR7, 8 and 9
Alzheimer’s disease - TLRs
TLR2 and 4
Atherosclerosis - TLRs
TLR2 and 4
TLR agonists
Infection - genital warts (TLR7)
Cancer - melanoma (TLR7 ligand)
Allergy - ragweed pollen (TLR9)
Vaccine adjuvant
TLR antagonists
Autoimmunity (TLR7,8,9)
Sepsis (TLR4)
Cancer
What are Nod-like receptors (NLRs)
NLR = nucleotide-binding leucine rich
- Cytoplasmic pattern recognition molecules
- Two major groups - NLRCs and NLRPs - ‘C’ stands for ‘caspase receruitment domain (CARD)’ and the ‘P’ stands for pyrin domain
Examples of NLRCs
- NLRC1 (NOD1)
- NLRC2 (NOD2)
How do NLRCs bind to peptidoglycans
- They have leucine rich domain which can bind to peptidoglycan which is present on the cell membrane of most bacteria
What do NOD1 and NOD2 detect
- NOD1 and NOD2 detect similar yet distinct peptides of peptidoglycan
What does NOD1 bind to
- NOD1 binds gamma-glutamyl diaminopimelic acid (iE-DAP) (Mainly Gm-ve bacteria)
What does NOD2 bind to
- NOD2 binds muramyl dipeptide (both Gm+ve and Gm-ve bacteria)
What is a NOD2 gain of function mutation linked to
- NOD2 gain of function mutation linked to early onset sarcoidosis where granulomas develop in the organs of the body
What is a NOD2 loss of function mutation associated with
- Associated with susceptibility to crohn’s disease, a chronic intestinal inflammatory disorder
Best characterised NLRP
- The best characterised is NLRP3 (NALP3)
What is NLRP3 activated by
- NLRP3 is activated by cellular stress; K+ efflux, ATP, reactive oxygen species and lysosomal damage
What is an inflammasome essential for the secretion of
- IL-1 and IL-18 secretion
What is an inflammasome
The inflammasome is a multiprotein intracellular complex that detects pathogenic microorganisms and sterile stressors, and that activates the highly pro-inflammatory cytokines interleukin-1b (IL-1b) and IL-18
Examples of pathogenic microbes and sterile stressors that can activate an inflammasome
- Uric acid crystals (gout)
- Asbestos
- Silica
- Amyloid beta (alzheimer’s)
- Islet amyloid polypeptide (type ii diabetes)
- Hemozoin (malaria)
What does inflammasome activation lead to
- Inflammasome activation leads to cleavage of pro-IL-1 and pro-IL-18 to allow secretion
What are gain of function mutations in NLRP3 caused by
- Caused by rare mutations in exon 3 of NLRP3 gene causing over production of IL-1
What can gain of function mutations in NLRP3 cause
- Cryopyrin-associated periodic syndromes (CAPS)
- eg Muckle wells syndrome and familial cold autoinflammatory syndrome
What is muckle wells syndrome
- Can occur spontaneously or be triggered by cold, heat, fatigue, or other stresses
- Symptoms of fever, rash, arthralgia, conjunctivitis, uveitis, sensorineural deafness and potentially life-threatening amyloidosis
What is familial cold autoinflammatory syndrome
- 1:1000000
- Triggered by exposure to cold
- Symptoms of fever urticarial rash with headache, arthralgia, and sometimes conjunctivitis
What are muckle wells syndrome and familial cold autoinflammatory syndrome treated with
- Both conditions can be treated with anakinra (IL-1RA)
What are RIG-I-like receptors (RLRs)
- RIG-I and MDA5 are sensors of cytoplasmic RNA, a replication intermediate for viruses
- They signal to induce pro-inflammatory cytokines and ifn
Features of RIG-I
- Binds to single stranded RNA containing 5’-triphosphate
- Recognition of: Flaviviruses(hep C) and orthomyxoviruses(influenza)
Features of MDA5
- Preferentially recognises long double stranded RNA
- Critical for picornavirus detection
- Mutations (rare) are beginning to be associated with IFN related diseases
How does expression of type I interferon genes occur
- Double-stranded DNA from viruses activates cGAS to produce cGAMP from ATP and GTP
- cGAMP or other bacterial-derived cyclic dinucleotides bind to the STING dimer present on the ER membrane and activate its signalling
- STING activates the kinase TBK1 to phosphorylate IRF3, which enters the nucleus and induces expression of type 1 interferon genes
What is SAVI
- Stimulator of interferon genes (STING)-associated vasculopathy with onset in infancy (SAVI) is an autoinflammatory disease caused by gain-of-function mutations in TMEM173, the gene that codes for STING
- Patients have abnormal inflammation throughout the body, especially in the skin, blood vessels, and lungs
What is an acute phase response induced by
- Induced by cytokines such as TNF, IL-6 and IL-1 during infection and inflammation
Where are acute phase proteins mainly produced
- Acute phase proteins are mainly produced by the liver
What do acute phase proteins induce
- Induces opsonisation/phagocytosis
- Can activate the complement pathway
Clinical measures used to to detect an acute phase response
- Raised erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP (a pentraxin)) are characteristic of an acute phase response and are used clinically to detect inflammation
Which TLR receptors only use the Myd88 adaptor protein
IL-1R, TLR5,7,8 and 9
Which TLR receptors use Myd88 and Mal only
TLR1/2
TLR2/6
Which TLR receptor uses TRIF only
TLR3
Which TLR receptors use Myd88, Mal, TRAM and TRIF
TLR4
