Inflammation, Inflammatory Disorders, and Wound Healing Flashcards
What are two stimuli for acute inflammation?
Infection - goal is eliminate pathogen
Tissue necrosis - goal is to clear necrotic debris
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What is the role of TLRs in innate immunity/acute inflammation? Give an example.
TLRs are receptors present on cells of the innate immune system (e.g. macrophages, DCs) that enable the cells to recognize microbial PAMPs (pathogen-associated molecular patterns). Activation of TLR stimulates upregulation of NF-kB to “switch on” innate immunity. A classic example is TLR4/CD14 of macrophages and LPS of gram-negative bacteria.
TLRs are ALSO present on cells of ADAPTIVE immunity (e.g. lymphocytes).
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How are arachidonic acid generated? What are the enzymes involved with generating AA metabolites? What functions do each category of metabolites carry out?
AA are released from phosphoplipid membrane by phopholipase A2, then acted upon by either cyclooxygenase or 5-lipooxygenase to produce either prostaglandins (PGs) or leukotrienes (LTs), respsectively.
PGs:
1) PGI2/D2/E2 - vasodilation and increased vascular permeability
2) PGE2 - pain and fever
LTs:
1) LTB4 - attracts/activates neutrophils
2) LTC4/D4/E4 - vasoconstriction, bronchospasm (slow reacting substances of anaphylaxis), and increased vascular permeability
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What four mediators of neutrophils?
Leukotriene B4
C5a
IL-8
Bacterial products
Where are mast cells distributed? What are three “triggers” of mast cell activation? How do the immediate and delayed responses of mast cells contribute to immune response?
Mast cells are widely distributed throughout connective tissues.
Activators of mast cells include:
1) Tissue trauma
2) Complement C3a and C5a
3) IgE cross-linking by antigen
Immediate response involves preformed histamine granules that mediate vasodilation (arterioles) and increased vascular permeability (post-capillary venules).
Delayed response involves AA metabolites, ESPECIALLY LTs, to help maintain innate immune response.
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What are the three complement pathways? What are the factors involved?
Pathways:
1) Classical - C1 binds IgG or IgM that is bound to antigen
2) Alternative - direct activation by microbial products
3) Mannose-binding lectin - MBL binds microbial mannose
All pathways result in activation of C3 convertase, which mediates C3 –> C3a and C3b. C3b produces C5 convertase, which mediates C5 –> C5a and C5b. C5b complexes with C6-9 to form MAC.
C3a and C5a - activates mast cells –> degranulation
C5a - chemotactic factor for neutrophils
C3b - opsonin for phagocytosis
MAC - C5b, C6-9. perforates microbial membrane
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What are the two inflammatory mediators of pain?
PGE2, generated from cyclooxygenase acting on arachidonic acid.
Bradykinin, generated from Hageman factor (XII)-activated kinin that cleaves high-molecular weight kininogen (HMWK). Bradykinin also mediates vasodilation and increased vascular permeability, similar to that of histamines.
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How is Hageman Factor (Factor XII) activated and what other pathways does it stimulate?
Released by liver in inactive form and activated by exposure to subendothelial or tissue collagen.
Activates:
1) Coagulation/fibrinolytic system - can lead to DIC, especially during severe gram-negative sepsis
2) Complement system
3) Kinin system
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Describe normal flow pattern within undilated blood vessel. How does that change with inflammation and what mediates that change?
Normally, in undilated vessels heavy molecules travel in laminar flow within the center of the vessel. However, upon activation of inflammation vasodilation of post-capillary venules occur (mediated by prostaglandins, histamines).
Vasodilation results in margination of these molecules, which then travel in the periphery of vessels to allow interaction with endothelial surface molecules.
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What is the mechanism of leukocyte rolling and what factors are involved?
Selectins are expressed on endothelial cells. P-selectins are released by Weibel-Palade bodies after stimulation by histamines. E-selectins are induced by TNF and IL-1.
Selectins interact with leukocytic sialyl Lewis X factor to mediate the rolling process.
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Which molecules are involved in the adhesion phase of neutrophil recruitment?
ICAMs/VCAMs are upregulated on endothelial cells by TNF/IL-1. Integrins are upregulated on leukocytes by C5a and LTB4.
Interactions between these two groups of molecules result in firm adhesion.
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What are the clinical findings of leukocyte adhesion deficiency (LAD)? Cause of deficiency?
LAD is commonly due to autosomal recessive defect of integrin CD18 on leukocytes, thereby impairing leukocyte adhesion.
Common findings include delayed umbilical separation, increased neutrophil circulation (decrease in marginal pool population in lungs), and increased bacterial infections + lack of pus formation.
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Which chemotactic factors mediate neutrophil transmigration and chemotaxis?
C5a, LTB4, IL-8, bacterial products
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Describe the mechanism of phagocytosis.
Phagocytosis usually “blind” action with no specificity, but can be guided by opsonins like IgG and C3b.
Phagocytosis starts off with extension of pseudopods from leukocytes that uptakes target to form phagosome. Phagosome then trafficks to meet and fuse with lysosome to form phagolysosome that leads to destruction of pathogen.
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Etiology for Chediak-Higashi syndrome? Clinical features?
Autosomal recessive mutation resulting in defect in protein-trafficking (“railroad track defect”).
Increased risk of pyogenic infections, albinism, giant granules in leukocytes, defective primary hemostasis, peripheral neuropathy
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Cause of chronic granulomatous disease? How do we screen for CGD and what is the mechanism for this test?
X-linked or autosomal recessive defect in NADPH oxidase –> poor O2 dependent killing.
Recurrent infections and granuloma formation with CATALASE-POSITIVE organisms: Staphylococcus aureus, Pseudomonas cepacia, Serratia marcescens, Nocardia, Aspergillus. (SPANS).
We use nitroblue tetrazolium test (NBT) with incubated leukocytes, which turns blue if NADPH oxidase can convert O2 to superoxide–colorless if defective.
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Mechanism in generating O2 dependent killing for leukocytes?
O2 –> superoxide by NADPH oxidase (oxidative burst)
Superoxide –> H2O2 by superoxide dismutase (respiratory burst)
H2O2 –> HOCl (bleach) by myeloperoxidase
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Mechanism for O2 independent killing?
Less effective than O2 dependent killing.
Involves enzymes present in leukocyte secondary granules: macrophage lysozymes, major basic protein in eosinophils.
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How is pus formed?
Pus is formed as a result of resolution of neutrophils. After controlling infection via phagocytosis/O2 dependent or independent killing mechanisms, neutrophils undergo APOPTOSIS and disappear within 24 hours after resolution of inflammatory stimulus.
Pus consists of dead neutrophils in fluid.
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How do macrophages home to site of infection? What is their primary mechanism of killing?
Arrive in tissue using similar mechanisms to neutrophils.
However, unlike neutrophils, their primary mechanism of killing is O2 independent killing with enzymes (lysozymes) in secondary granules.
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Describe the means (and factors involved) by which macrophages mediate the following processes:
1) Resolution and healing
2) Continued acute inflammation
3) Abscess
4) Chronic inflammation
1) If neutrophils do a good job in clearing infection, macrophages secrete anti-inflammatory cytokines (IL-10 and TGF-B).
2) If infection requires more neutrophils to manage, macrophages secrete neutrophil-recruiting chemotactic cytokine IL-8.
3) If infection/acute inflammatory process needs to be walled off to protect organ macrophages can mediate formation of fibrosis around area with fibrogenic growth factors/cytokines.
4) If neutrophils are insufficient in clearing infection (e.g. virus), macrophages can activate CD4 T-cells via MHC II presentation.
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Give a brief description of T cell development. What are the minimum requirements for general T cell activation.
T cell progenitors produced in the bone marrow.
In thymus, they are “educated” and undergo receptor rearrangement to become either CD4+ OR CD8+ T cells. The TCR complex (TCR and CD3) used for antigen surveillance.
Activation requires:
1) Antigen/MHC complex binding
2) Second additional signal
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CD4+ helper T cell activation? Different subsets and cytokines released?
Activation: APCs (DCs or macrophages) process extracellular antigens and present on MHCII (APCs) to CD4+. Secondary signal involves CD28 on CD4+ T helper cells and B7 on APC activates TC to secrete different cytokines depending on helper cell subtype.
Th1 subset:
IL-2 - aids in CD8 activation (second signal) + TC GF
IFN-gamma - macrophage activation
Th2 subset: IL-4 - IgG --> IgE class switch IL-5 - BC maturation to plasma cells + class switch to IgG. Also plays role in eosinophil maturation and chemotaxis. Class switch to IgA. IL-10 - suppresses Th1 phenotype
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CD8+ cytotoxic T cell activation? Mechanism in cell killing?
Activation: First signal involves TCR complex and MHCI/Antigen interaction. MHCI present on ALL nucleated cells and platelets. Second signal is IL-2 from Th1 subset.
Killing via caspase activation and apoptosis. Achieved by either CD8 perforin/granzyme release or extracellular signaling pathway with TC FasL/target Fas interaction.
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