Chapter 3: Cellular Mechanisms Of Innate Immunity Flashcards
What are PAMPs? What are DAMPs? How are they recognized?
- Pathogen associated molecular patterns
- Damage associated molecular patterns
- Recognized by PRRs
What are the four main groups of PRRs?
- Free receptors in serum
- Mannose binding proteins and ficolins
- Membrane-bound phagocytic receptors
- Membrane-bound signaling receptors
- Cytoplasmic signaling receptors
What do macrophages, granulocytes, and dendritic cells do when they encounter a pathogen?
Macrophage
- In connective tissue
- Different names based on tissue
- Mature from monocyte
Granulocytes
- Neutrophils have greatest phagocytic capacity
Dendritic cells
- Conventional antigen-presentation
- Plasmacytoid: release antiviral cytokines
What are three types of phagocytic receptors?
C-lectin type like
- Dectin-1 (recognize fungi)
- Mannose receptors (fungi, bacteria, viruses)
Scavenger receptors
- Class A
- receptors have collagenous structure
- recognize Recognize bacterial components
- Class B
- Bind to fatty acids
Complement and FC receptors
What is phagocytosis? Is it the same in neutrophils?
- Pathogens and opsinins bind to receptors
- Pathogen is internalized and fuzed with lysosomes
- Acidic, antimicorbial peptides, Auperoxide and nitic oxide radicals
Neutrophils: Phagosomes fuse w/ primary and secondary granules
What is an important primary granule in a neutrophil?
- Myeliperoxidase
What type of receptor do phagocytes express to stimulate antimicrobial killing?
- G protein coupled receptor
- Activates intracellular GTP-binding proteins
- Direct response to PAMPs, anaphylatoxins (C5a), leukotrienes and chemokines
- fMet-Leu-Phe (fMLF) receptor and C5a receptor
What is fMLF receptor and what does it do?
- PRR
- High affinity towards fMLF and other motifs
- Protein synth of bact starts with fMet
- Promotes the production of microbial reactive oxygen (ROS) in phagolysosome
- Induces NADPH oxidase assembly (and nitric oxide synthase)
How does GPCR activation result in ROS generation?
- Before ligand binds, G protein is not associated
- Binding of ligand allows association with G protein by replacing GDP w/ GTP
- G protein dissociates and forms alpha and beta-gamma subunits to activate other proteins
- GTP cleavage allows for the formation of G protein once more
How does the production of ROS result in the destruction of bacteria? What happens in neutrophils?
- Rapid production of superoxide anions by NADPH oxidase results in increase O2 consumption known as respiratory burst
- Superoxide anions converted into hydrogen peroxide
- In neutrophils, hydrogen peroxide is converted by myeloperoxidase from the primary granule to hypochlorite
What is the role of Rac in phagocytosis?
- fMLF binds to GPCR which signals RAC to induce assembly of NADPH oxidase
- NADPH oxidase leads to the generation of O2-
What are NETs?
- Neutrophil extracellular traps
- meshwork of nuclear chromatin release in extracellular space and undergo apoptosis trapping bacteria which enhances phagocytosis
What are the three main functions of pathogen recognition by innate immune cells?
- Deliver effector molecules(compliment) and cells( neutrophils, monocytes, etc.)
- Induce local blood clotting to prevent spread
- Promote repairment of injured tissue after infection
What are the four types of changes that can occur in local blood vessels during inflammation?
Vasodialation
- Increase/decrease vascular diameter to slow or speed up blood flow
- redness and heat
Activated endothelial cells (cell-adhesion molecule expression)
- Promotes binding of leukocytes (neutrophils first then monocytes)
- Monocytes can become either inflammatory monocytes or dendritic cells, and release inflammatory cytokines
- Tissue damage and pain
Activated endothelial cells (increase vascular permeability)
-Allow fluid and effector molecules (compliment proteins) to cross
- Cause swelling/edema and pain
Clotting of micro vessels
- Activation of platelets or coagulation cascade to limit spread of infection
What are TLRs? What do they do? What do they look like? Where are they found?
- Toll like receptors (similar to toll in flies)
- Induce expression of host-defense mechanisms
- Horse shoe shaped transmembrane proteins on the surface or inside of endosome/phagosome
- Found in leukocytes, stromal cells, and epithelial cells
What happens when a ligand binds to a TLR?
- Dimer forms
- Either Homo or hetero dimer
How do TLRs become functional?
- TLR-3,-7,-8,-9,-11,-12,-13 all require transmembrane transport protein UNC93B1 to reach endosome
- Nucleic acid sensing TLRs are cleaved in endosome to become functional
- This mechanism is to prevent host’s nucleic acids from activating the receptor
Are TLRs all able to independently recognize bacterial lipopolysaccharides?
- Some are able to bind directly to ligand while others may require accessory proteins
Ex. TLR-4 requires LPS, CD14, and MD-2
What does LPS look like?
- Multiple fatty-acyl chains linked to glycan head
- Binds to MD-2
- Free chain is able to bind to complex of another T:LR during dimerization
What is the purpose of TLR activation and what does it do?
- TLR activation induce expression of inflammatory cytokines and type 1 interferon
- Induce chemokines and antimicrobial peptides
- TLR interacts with adaptor proteins that facilitate signal transduction by recruiting signal molecules
What does signaling activation of TLRs result in? (NFkB, AP-1, IRF)
NFkB - induces pro-inflammatory cytokines and chemokines
A(ctivator)P(rotein)-1 - induces pro-inflammatory cytokines and chemokines
I(nterferon) R(egulatory) F(actor) - induce type-1 interferons
Describe in general terms how cytokine genes are produced.
- Dimerization of TLRs results in activation of downstream ligase
- Phosphorylation of a complex leading to the release of NFkB
- NFkB enters nucleus inducing expression of cytokine genes
What do the cytoplasmic innate receptors RIG-1, RIG-1-like receptor (RLR), NOD-like receptor (NLR) do?
- Activate transcription factors NFkB and IRF
What does RIG-1 do?
- Detect cytoplasmic viral RNAs and activate MAVS (Adaptor proteins)
- Induction of T1 interferons and pro-inflammatory cytokines
- Activation of RIG-1 results in IRF3 and NFkB
What does activation of cGAS-STING result in?
- Production of type 1 interferon
What is an important function NLRs (intracellular sensors) carry out?
- Activate NFkB, release different pro-inflammatory cytokines which trigger pyroptosis
How do NLR proteins react to infection and/or cellular damage?
- Form inflammasome that induce cell death and secretion of inflammatory cytokines
What are the three types of cytokine signaling that can occur?
Autocrine, paracrine, endocrine
How is cytokine signaling regulated?
Pleitropy - One cyto can have different effects on different cells
Redundancy - Many cyto have same effect
Synergy - Cyto cooperate to enhance signaling
Antagonism - Cyto inhibit actions of others
What are the members of cytokine families?
- IL-1 family
- Hematopoietin superfamily
- Tumor Necrosis Factor (TNF)
- Chemokine
- Interferons
What are the properties of IL-1 family?
- Notable: IL-1a,1B,18,33
- Proprotein cleaved to make mature cytokine
- Pro-inflammatory functions
What are the properties of Hematopoietin superfamily?
- Function in immune system and growth/development of hemopoietic cells
- Notable: IL-6, GM-CSF
What are the properties of Interferons?
- Type I,II,III
- Notable IFN-alpha, beta, INF-gamma
What are the properties of TNF?
- Membrane bound (some can be released)
- Notable: TNF/TNF-alpha
- Inflammatory cytokine that can induce apoptosis
What signaling pathway are Type I and Type II receptors involved in?
- JAK-STAT signaling pathway
- Interferon receptors
What are the cytokine receptors of the hematopoietin superfamily associated with?
- They’re associated with JAK tyrosine kinases which activate STAT transcription factors
What happens in the JAK-STAT pathway?
- 4 components of JAK, 7 STATs
What type of cytokines can amacrophage secrete?
- IL1 Beta, TNF,IL-6, CXCL8,IL-12
What do CC and CXC chemokines do?
CC: promote migration of monocytes,lymphocytes, and other cell types
CXC: Promote migration of neutrophils
What do cell adhesion molecules control?
- Control interactions bt leukocytes and endothelial cells during inflammatory response
- Selectins on activated endothelial cells initiate leukocyte-endothelial cell interaction by binding to ligands of leukocyte (cause rolling)
- Intracellular adhesion molecules (ICAMs) on activated endo cells bind to integrins on leukocyte forming tighter adhesion which arrests rolling cell
What drives endothelial activation? What is it? How long does it take? What does TNF do?
- Driven by macrophage produced cytokines (especially TNF)
- When granules are rapidly externalized from endo cells when TNF, C5a, leukotriene B4, or histamine bidn to receptor
- Occurs within minutes
- Induces transcription of E-selectin and later other adhesion molecules
How do neutrophils manage to cross the blood vessel and enter the inflamed tissue?
- Selectin-mediated adhesion is weak which allows for leukocyte rolling
- Chemokines cause conf change which allows for tight binding as a result of activated integrins
- Diapedesis (CD31) is when the neutrophil starts to make its way into the tissue and eventually fully migrates in
What can result if TNF is systematically released?
- Cytokine can trigger local containment but systemic release induces shock
What is acute phase response?
- TNF, IL1B, IL-6 (cytokines)initiate acute phase response
- Change in blood proteins during inflammation, infection, trauma
- Acute phase proteins increase in blood while certain proteins decrease in []
What are additional biological activities of TNF, IL-1B, IL-6?
- Induce fever and mobilize neutrophils
What are the two sources for neutrophils? What happens if there is an increase in neutrophils circulating in blood pool?
- Bone marrow
- Production of neutrophils and main reserve
- Marginating Pool
- Neutrophils attached to cells throughout the body
- Increase in neutrophils that enter circulating pool leads to leukocytosis/neutrophilia
What are 4 consequences of innate immune activation?
- Fever caused by endogenous pyrogens (TNF, IL-1B, IL-6
- Fever caused by exogenous pyrogens (LPS)
- Cytokine induced expression of COX-2 required to make Prostaglandin E2 (PGE2)
- PGE2 acts on neurons of hypothalamus
- Heat production due to catabolism of brown fat
- Heat retention by vasoconstriction
- heat production from shivering
What are type I and type III interferons?
Type I:
- IFN A and B
- Produced in almost all cell types
- Produced mainly by palasmacytoid dendritic
- Autocrine and paracrine signaling
- STAT1 + STAT2 + IRF9 = TF ISGF3 to promote ISRE
Type II:
- Interferon - ƛ
- Receptors restricted to largely epithelial cell (mucosal immunity)
- Similar signal pathway and ISG as Type I
What effect do autocrine and paracrine signaling have on ISGs
Autocrine: ISGs block ongoing infection
Paracrine: ISGs act to prevent infection
What are type II interferons?
- IFN-γ
- Defend against intracellular pathogens
- tuberculosis
- Produced by CD4 TH1 cells, CD* T cells, NK cells
- Activate macrophages
