9/19 Flashcards
Properties of Inflammatory Mediators
Tightly controlled: made only in response to stimulus like microbes or material from necrotic cells, inflammation only occurs when needed
Reaction is specific: trigger well defined receptors and signaling pathways, but most unknown
Short lived: quickly decay, enzymatic cleavage, scavenged, or inhibited
Cascading Effect: release of one mediator can stimulate the activation of other mediators that can amplify or counteract the initial response
Plasma
Colorless fluid part of blood in which RBCs and WBCs are suspended
Water, electrolytes, enzymes, clotting factors, and some proteins
Contains fibrinogen, serum doesn’t have fibrinogen (doesn’t have the clotting factors)
Basics of Plasma Derived inflammatory Mediators
End products of a group of serine proteases produced in the liver
Zymogens activated in a stepwise manner by a previously activated enzyme, usually need proteolytic cleavage
Zymogens in circulating plasma and sequestered in ECM of tissues
Simplified Complement Cascade
Three ways for proteolytic cleavage of C3- by C3 Convertase-
1. Classical: fixation of C1 to antibody bound to antigen
- Alternative: microbial surface molecules like LPS or endotoxins in absence of antibody
- Lectin: plasma mannose-binding lectin binds to carbs on microbes and directly activates C1
C3b does positive feedback on Alternative pathway, opsonization of neutrophil/macrophage after binding to microbe surface, activates C5 convertase
C5b helps form membrane attack complex (MAC) with C6-C9
C3a and C5a involved in inflammation and histamine release, recruits and activates leukocytes to kill microbes, microbe permeable to water and ions then lysis
C5a is chemotactic agent for leukocytes and activates the lipooxygenase pathway of cell derived m ediators
Kinin System
Factor XIIa from the coagulation cascade converts prekallikerin to kallikerin, which cleaves high molecular weight kininogen (HMWK) into bradykinin
Bradykinin binds to B1 receptors and activates endothelial cells to get NO and prostaglandin synthesis that leads to vascular permeability, vasodilation, pain, and contraction of nonvascular smooth muscle like bronchi/uterus
HMWK can activate Factor XII to get positive feedback
Kinin System Regulation
- Kininase: rapidly inactivates bradykinin
- ACE: inactivates bradykinin in the lungs, ACE inhibitors lead to higher bradykinin to cause angioedema of the face and chronic cough due to contraction of smooth muscle in the bronchi
Coagulation System
Factor XII (Hageman factor) circulates in the blood and becomes activated when touch negative thing like collagen, basement membrane, or activated platelet that arise during inflammation
Clotting factors activate thrombin to convert fibrinogen to fibrin for a durable blood clot
Enhances inflammation: thrombin induces expression of cell adhesion molecules and production of cytokines, chemokines, prostaglandins, NO, and platelet activating factor
Fibrinolytic System
Curbs clot formation to prevent it from getting out of hand and keeps its area focused
Kallikerin and plasminogen activator (from Endothelium, leukocytes, and other tissues) cleave plasminogen into plasmin
Plasmin lyses blood clots, cleaves C3 to get fibrin split products which increase vascular permeability, also can activate Factor XII
Defense Mechanism of innate Immunity based on Site of Infection
Extracellular-
Interstitial, blood, lymph: complement, macrophages, neutrophils
Epithelial cell surfaces: antimicrobial peptides
Intracellular-
Cytoplasmic: NK cells
Vesicular: activated macrophages
Physical Barriers of Innate Immunity
Goblet cells secrete mucus that trap microorganisms and prevent them from penetrating epithelial barriers
Tears, urine, saliva, gastric acid, mucus, coughing, sneezing
Types of Innate Immunity
Physical barriers
Coagulation and platelets
Defensins
Innate immune cells
Coagulation and Platelets for Innate Immunity
Coagulation System: plasma enzymes that form blood clots to immobilize microorganisms and prevent them from entering blood/lymph, leads to bacterial destruction
Platelets: release prostaglandin, enzymes, GFs, and cytokines that help with anti-microbe defense, wound healing, and inflammation
Activate neutrophils and dendritic cells
Defensins
Small antimicrobial peptides, penetrate microbial membranes and disrupt integrity
Alpha defensins: made by neutrophils, paneth cells in the intestinal crypts maintain gut microbiome
Beta defensins: broadly expressed by all leukocytes and epithelial cells in many tissues
Macrophages
Express several receptors specific for bacterial constituents: mannose, LPS, Toll like Receptors, CR3, Glu can, scavenger
Bacteria bind to macrophage receptors and get digested, present antigens from the degraded cells
Reside in tissues and produce cytokines at infection site to signal other immune cells to come
Have TLR4 for LPS, induce inflammatory cytokine transcription
Microglia in NS, osteoclasts in bone, Kupffer cells in liver, and Langerhans cells in skin
Dendritic a Cells
Phagocytic cells, antigen presenting cells
Most potent activator of T cells
Can traffic and transport antigens
Toll-like Receptors
TLR3 recognizes dsRNA in viruses and are often in endosomes
TLR4 recognizes LPS
TLR9 recognizes unmethylated CpG DNA
On dendritic cells and macrophages induce inflammatory cytokines like IL-1/6, TNFalpha, IFNgamma
On virally infected cells induce gene transcription of Type 1 interferons like IFNalpha/beta
Induces expression of MHC II and costimulatory molecules (CD80/86) in dendritic cells and macrophages
Major Histocompatibility Complex
Proteins expressed on cells that bind peptide antigens and present them to T cells
MHC I: expressed by most cell types
MHC II: expressed by dendritic cells, macrophages, and B cells
Respiratory Burst
Metabolic change accompanied by transient increase in oxygen consumption that occurs in neutrophils and macrophages when they phagocytose pathogens
Septic Shock
Severe shock caused by systemic release of TNFalpha after bacterial infection in blood
Macrophages activated in the liver/spleen secrete TNFalpha into bloodstream
Systemic edema causes decreased blood volume and hypoprotenemia
Disseminated intravascular coagulation leads to wasting and multiple organ failure
More likely if heterozygous for TLR mutation
Cytokines Induced by TLR Signaling in Macrophages
IL-6: fever, induces acute Phase protein production by hepatocytes
TNFalpha: increases vascular permeability that increases entry of complement/cells to tissues and increases fluid draining to lymph nodes
Fever, mobilization of metabolites, shock
IL-1beta: activates vascular endothelium/lymphocytes, local tissue destruction, increase access of effector cells
Fever, production of IL-6
CXCL8 (IL-8): chemotactic Factor, recruits neutrophils/basophils to site of infection
IL-12: activates NK cells
Neutrophils
Most abundant WBC, migrate rapidly to site of infection, high energy cells with short life
Phagocytose and then degrade microorganisms with toxic granules, use respiratory burst
Phagosome fuses with azurophilic/specific granules, pH of phagosome incresse and bacterium is killed, pH of phagosome decreases and then fuses with lysosome, neutrophil dies by apoptosis and eaten by macrophage
Attracted by IL-8 to site of infection
Type I Interferons (IFNalpha/beta)
Induced by most infectious agents but do worse than other interferons at limiting viral infections
TLR signaling by an infected cell initially induces INFbeta expression, secretes IFNbeta and binds to the surface of neighboring cells and itself
IFN receptor signaling induces production of INFalpha by infected cells and INFaplha/beta by neighboring cells
Type I interferons inhibit viruses from entering cells and limits viral replication in cells
Natural Killer Cells
- Healthy cells express MHC class I receptors that bind to an inhibitory receptor on the NK cell and the healthy cell lives, all cells have MHC I receptors
Some viruses remove MHC I receptors from cells, an activated receptor binds to a ligand on the virally infected cell
Release lyric granule with perforin to put hole in PM and granules that damage intracellular structures to induce apoptosis
- Normal cells don’t express MIC receptors, virally infected cells express MIC receptors that bind to NKG2D receptor on NK cell, release lyric granules
MIc also comes from trauma or malignancy
Mast Cells
Express Fcepsilon receptors that bind IgE, allergen crosslinks IgE, mediators like histamine are released
IgE often for allergens and parasites
Basophils
Have Fcepsilon receptors that have IgE bound
Bind parasites and allergens, release inflammatory mediators like IL-4 that is for T cells
Eosinophil
IgE receptors to limit parasite infections, but can contribute to allergies
Arachidonic Acid Metabolites STP
Ligand like C5a bind to a cell receptor and activate phospholipase C and the IP3/DAG pathway with Ca2+, PKC activates MAPK which then activates phospholipase A2 (PLA2)
PLA2 releases arachidonic acid from the membrane, AA converted into eicosanoids
Cyclooxygenase: converts AA to prostaglandins
Lipoxygenases: convert AA to leukotrienes or lipotoxins
Convert these basic eicoanoids into cell specific eicosanoids which can bind to G protein coupled receptors on other cells
Steroids inhibit Phospholipase A2
Cyclooxygenase Pathway
Involved in vascular and systemic reactions of inflammation
Occurs in mast cells, macrophages, endothelial cells, and other cells
COX-1 (constitutively active) and COX-2 (Induced by IL-1 / TNFalpha, inhibited by IL-4) do cyclooxygenase to convert AA into Prostaglandin G2 then H2, inhibited by aspirin
PGI2 (Prostacyclin): made by endothelial cells, vasodilation, inhibits platelet aggregation
TxA2 (Thromboxane): made by platelets, vasoconstriction, bronchoconstriction, promotes platelet aggregation
PGD2: mast cells, vasodilation, increase vascular permeability, bronchoconstriction, eosinophil recruitment
PGE2: in tissues and does classic signs of inflammation, pain, fever cuz interact with IL-1, vasodilation, increase vascular permeability
PGF2alpha: uterine smooth muscle contraction and initiates parturition, bronchoconstriction
Lipoxygenase Pathway: Leukotrines
Makes leukotrienes for inflammation
Arachidonic acid converted to 5-lipoxygenase then 5-HPETE to become the different leukotrienes
LTB4: chemotactic agent for neutrophil aggregation to Endothelium and activates them by helping to make their ROS
LTC/D/E4: bronchconstriction, vasoconstriction, increase vascular Permeability more than histamine
Lipoxygenase Pathway: Lipoxins
Inhibit inflammation and neutrophil chemotaxis/adhesion to endothelial cells
Transcellular synthesis: leukocyte converts AA to LTA4 and then it diffuses into platelet where it becomes 12-LOX, finally becomes LXA4 and LXB4
Inhibition of Eicosanoid Synthesis
Aspirin and other NSAIDS are cyclooxygenase inhibitors that prevent prostaglandin synthesis, don’t work on Lipoxygenase
Platelet Activating Factor
Derived from membrane lipids of neutrophils, monocytes, activated endothelial cells, platelets, and basophils
Phospholipase A2 cleaves membrane lipid into AA and lyso-PAF that can be put back into the membrane or turned into activated PAF
PAF short lived and binds to PAF receptor (GPCR) that’s constitutively expressed on platelets, endothelial cells, and leukocytes
Functions-
1. Enhance platelet aggregation and degranulation
- Activates leukocytes: leukocyte endothelial cell adherence, mobility, chemotaxis, oxidative burst, and synthesis of lipid mediators/cytokines
- Activates endothelial cells: increase vascular Permeability, vasodilation via NOS
Nitric Oxide
Inducible NOS in macrophages, neutrophils, and endothelial cells by IL-1, TNF, and IFN-gamma
Helps kill microbes via free radical mechanism involving peroxynitrite
Oxygen dependent Pathway with L-Arg
Antagonist for platelet aggregation and adhesion, and also against leukocyte adhesion
Smooth muscle cells: makes cGMP from guanylate cyclase, decreased sensitivity of myosin to calcium induced contraction, muscle relaxation and vasodilation
Histamine
Vasoactive: dilation of arterioles, increases venule permeability
Mast cells line blood vessels, store large granules of histamine, rapid since already made
Release Factors for Histamine-
1. Physical injury: trauma, hot/cold
- Antibody binding, IgE in allergic reactions
- C3a and C5a
- Histamine releasing proteins from leukocytes, substance P, IL-1, IL-8
Histamine Receptors-
H1 Receptor on Endothelial Cells: contraction of myosin to create vascular permeability
H1 on lung Smooth Muscle Cells: brinchoconstriction
H1 on eosinophils: stimulates chemotaxis
H2 on vascular smooth muscle: relaxation and vasodilation, inhibits eosinophil chemotaxis
Anaphylatoxins
C3a and C5a induce inflammation
Helps mast cells degranulate
Increased permeability of blood vessels increases fluid leakage and extra version of complement/plasma proteins
Monocytes and neutrophils migrate into tissues, microbicidal activity of macrophages and neutrophils increased
Complement Fixation
Attachment of C3b to pathogen surface which labels the pathogen for phagocytosis
Alternative Complement Pathway: C3
- C3 made by liver and constitutively present in blood, hydrolyzed in blood naturally, binds factors B and D in local environment of microbes to form C3 comvertse (Bb)
C3 converts cleaves C3 into C3a and C3b
C3b binds to surface of pathogens (complement fixation), positive feedback loop cuz forms C3bBb that can recruit other C3s and cleave them to bring more C3b to pathogen surface
CR1 receptor on macrophages bind C3b coated pathogens and phagocytose into lysosome
Alternative Complement Pathway: C5
Directly kills pathogen
Alternative C5 convertase (C3b2Bb on pathogen surface) cleaves C5 into C5a and C5b
Membrane Attack Complex: C5b brings C6-8 to pathogen surface then C9 comes to form pore
MAC not have much clinical significance if deficient like with Japs
Lectin Complement Pathway
Second pathway, after alternative pathway
Mannose binding lectin is attached to Mannose Associated Serine Protease (MASP-1 and 2)
Mannose binding lectin binds to pathogen surface, MASP-2 cleaves C4 and C2, C4b and then C2a binds to pathogen surface to form Classical C3 Convertase
Classical C3 Convertase cleaves C3 to do normal alternative pathway stuff
Classical Complement Pathway
Last pathway to be activated
C1 has three parts: C1q,r,s
Cytokine Classification
- Type I Cytokine Family-
A: Short-chain Cytokine: Growth hormone, EPO, prolactin, leptin
B: Long-chain Cytokine: IL-2,3,4,6,12 - Type II Helical Cytokine-
A: interleukins: IL-10,22,26, produced by leukocytes
B: interferon: IFN type I is IFNalpha/beta and type II is IFNgamma, help cells resist viruses - IL-1 Family: IL-1beta,18,Ra, made by leukocytes
- TFN-Family: TFNalpha and LTbeta
- Chemokines- guide WBCs where they’re needed
A: CC19,20,25 and CXCa-b,12,14 plus IL-8
IL-2 Receptor Signaling
Induces T cell proliferation
Naive T cells express low affinity IL-2 receptor (beta/gamma chains), activated T cells have high affinity IL-2 receptor (alpha/beta/gamma)
Activated T cells also secrete IL-2 via autocrine manner, cause STP with a JAK Stat pathway, activate proto-oncogene and cyclins to cause T cell proliferation
Interferon-Gamma Receptor Signaling
Use JAK-STAT pathway
Regulates expression for antiviral, inflammatory, and anti-tumor responses
Enhance expression of MHC, TFs and cytokine receptor for T cell differentiation, induce isotype switching in B cells to produce specific antibodies
IL-8 Receptor Signaling
CXCR1/2 receptors on neutrophils bind IL-8, neutrophils travel through blood, binding to IL-8 brings to site of infection
IL-8 (CXCR8) is made by macrophages from a STP involving a TLR, neutrophil binding to IL-8 promotes extravasation of neutrophils into site of infection
IL-8 binds to a GPCR (normal for chemokines), activate genes that enhance ability of neutrophils to enter infection site and also phagocytose/kill pathogens
