Oral Immunology - 0518 - L5 6

  1. Antimicrobial peptides in mucosal innate host defense - a model
    • Recognition - Patterns on pathogen are recognized by TLRs and other receptors
    • Signaling - Signal transduction resulting in activation of transcription factors
    • Products - Upregulation of defensin (and other) genes
    • Response - Defensins and other inflammatory mediators modulate an inflammatory response
    • Differential activation by commensal and pathogenic organisms
  2. Removal of colonized pathogens in the circulation
    • Cell recruit - Neutrophils and macrophages are recruited by cytokines, stimulated by LPS and other signals
    • Phagocytosis - These cells phagocytose the organisms signals
    • IC Kill - Pathogens are killed intracellularly by a variety of mechanisms
  3. Macrophages have many different cell-surface receptors by which they ________ and ___________
    • recognize and bind to pathogens
    • enable phagocytosis and intracellular digestion by fusing phagosome with lysosome to form phagolysosome
  4. Neutrophils' granules
    • Primary/azurophilic
    • - lysosomal enzymes
    • - myeloperoxidase
    • - lysozyme
    • - BPI - bactericidal permeability increasing protein (antimicrobial peptide)
    • Secondary
    • - alkaline phosphatase
    • - lysozyme; lactoferrin
  5. NADPH oxidase
    • • Located in plasma membrane
    • • Dormant in unstimulated cells
    • • Activated by protein phosphorylation
    • • Inactive -> Chronic Granulomatous Disease
    • - Oxygen and nonoxygen pathways
    • - Oxygen pathway: NADPH oxidase is used, involved with hexose monophosphate shunt (HMP shunt)
  6. Oxygen-dependent antibacterial mechanisms - Respiratory burst:
    • Stimulation of HMP shunt pathway
    • Production of superoxide, hydrogen peroxide, Hydroxyl radical
    • H2O2/chloride/MPO
    • Products can also be secreted to kill extracellular bacteria
  7. Respiratory Burst - 1: Superoxide
    • Increase in O2 consumption upon stimulation
    • Production of superoxide:
    • – 2 O2 + NADPH ---> 2 O2.- +NADP+ +H+
    • NADPH oxidase
    • – causes increase in HMP pathway
  8. Respiratory burst - 2: H2O2
    • 2O2.- + 2H+ --> H2O2 + O2
    • Spontaneous or catalyzed by superoxide dismutase
    • Microbicidal and cytotoxic
    • Excess of H2O2 scavenged by catalase and glutathione
    • Interacts with MPO and Cl-:
    • – H2O2 + Cl- --> OCl- + OH-
  9. Respiratory Burst - 3: Hydroxyl radical
    • H2O2 + Fe2+ --> OH + OH.
    • Enhanced by lactoferrin (Fe binding)
  10. Oxygen dependent antibacterial mechanisms - summary
    • O2 -> O2- (superoxide ion; by NADPH oxidase)
    • O2- -> H2O2 (superoxide dismutase, SOD)
    • H2O2 -> ClO-, .OH (peroxidase, iron)
  11. Myeloperoxidase
    • Packaged in azurophilic granules
    • – 1-5% of the dry weight of the cell
    • Requires heme and glycosylation for activity
    • Green in color
    • Reacts with H2O2 and halides to form hypohalous acids (HXO; X=Cl, Br, or I)
    • MPO-H2O2-halide system in the phagosome
  12. Oxygen-independent antibacterial mechanisms
    • BPI (Bactericidal/Permeability Increasing Protein
    • Lysozyme and lactoferrin
    • Myeloid Antimicrobial peptides
    • –Defensins
    • –Cathelicidin
  13. Bactericidal/Permeability Increasing Protein (BPI)
    • found in azurophilic granules
    • potent LPS binding and inhibition
    • bactericidal against G(-) bacteria
  14. Lysozyme and Lactoferrin
    • Antimicrobial proteins
    • Found in secretions including saliva
    • Lactoferrin appears to be associated with anti-caries activity
  15. Myeloid Defensins
    • Highly concentrated in azurophilic granules of neutrophils in man, rat, guinea pig, rabbit
    • Numerous isoforms in each cell
  16. Infection stimulates macrophages to
    • release cytokines and chemokines, initiating an inflammatory response
    • Cytokines -> dilate local small blood vessels
    • Endothlium increases adhesion expression, attract leukocytes to periphery of blood vessels.
    • Leukocytes extravasate
    • Blood clotting
  17. Activated macrophages secrete a range of important cytokines:
    IL-1b, IL-6, CXCL8, IL-12, and TNF-a.
  18. IL-1b
    • Activates vascular endothelium
    • Activates lymphocytes
    • Local tissue destruction
    • Increases access of effector cells
    • Systemic: Fever; Production of IL-6
  19. IL-6
    • Lymphocyte activation
    • Antibody production
    • Systemic: Fever; Induces acute-phase protein production
  20. CXCL8
    • chemokine
    • Chemotactic factor recruits neutrophils, basophils, and T cells to site of infection
  21. IL-12
    • Activates NK cells
    • Induces the differentiation of CD4 T cells into TH1 cells
  22. TNF-a
    • Activates vascular endothelium and increases vascular permeability, which leads to increased entry of lgG, complement, and cells to tissues and increased fluid drainage to lymph nodes
    • Systemic: Fever; Mobilization of metabolites; Shock
  23. Innate immunity against viruses: NK cells
    • Lyse virus-infected cells
    • Secrete cytokines (IFN-γ)
  24. NK cell lysis
    • Virus-infected and tumor cell have no or fewer normal MHC I (almost all normal cells have it, except RBC), allowing for recognition by NK cells (disabling inhibitory receptors that inhibit signals from activating receptors)
    • Virus-infected cells secrete IFN-a and b - activate NK cells
    • Perforins creates pores in target cells
    • Granzymes enter through pores and cause apoptosis
  25. Complement
    • Circulating plasma proteins that bind membranes
    • Microbial membranes lack inhibitory proteins, and are subjected to lysis
    • stimulates influx of neutrophils
  26. ILCs and _____ are different __________.
    • NK cells
    • innate lymphoid subgroups
    • ILCs more localized; NK tends to move around
  27. ILC_ is similar to NK cells in that _________.
    • 1
    • induced by IL-12
    • secretes IFN-γ
  28. Classical pathway via _______, lectin pathway via _____, and alternate pathway via ______, to activate ______.
    • Ag:Ab complexes
    • lectin (instead of Ab) binding to pathogen surfaces
    • pathogen surfaces (absence of Ab)
    • complement
  29. For all pathways, following complement activation:
    • recruit immunocompetent and inflammatory cells
    • opsonization of pathogens
    • kill pathogens
  30. _______: a key link between the innate immune system and the adaptive immune system
    Dendritic cells
  31. Innate immunity and periodontal disease
    • Adult onset periodontitis
    • – Genetic component
    • – Immunosuppression
    • – Introduction of pathogenic bacteria (e.g., P. gingivalis)
    • Localized Aggressive Periodontitis
    • – Genetic component
    • – Most often associated with (commensal) Aa: Bacterial encoded virulence factors
    • Papillon-Lefevre Syndrome
    • - Lack of mature, active cathelicidin (LL-37)
    • - Defect in Cathepsin C, which activates Cathepsin G, which induces maturation of LL-37; predispose to bacterial infection
    • Morbus Kostmann
    • - Inherited, complete lack of cathelicidin (LL-37) in neutrophils
    • - Severe gingivitis and periodontitis
  32. Innate immunity and LAP
    • Aa expresses leukotoxin (which kills leukocytes)
    • ~70% of patients exhibit defective neutrophil chemotaxis
    • –> reduced capacity to respond to infection
    • –> reduced killing capacity of neutrophils
  33. P. gingivalis LPS is recognized by _____.
    TLR2, not TLR4
  34. Innate immunity effectors are found in ____ sites and in _______ cells.
    • epithelial
    • myeloid
  35. Four characteristics of inflammation
    pain, heat, redness, swelling
  36. Innate Host Defenses Against Infection
    • Anatomical barriers
    • – Mechanical factors
    • – Chemical factors
    • – Biological factors
    • Humoral components
    • – Complement
    • – Coagulation system
    • – Cytokines
    • Cellular components
    • – Neutrophils
    • – Monocytes and macrophages
    • – NK cells
    • – Eosinophils
  37. Bordet's experiments leading to the discovery of ____.
    • complement
    • experiment on lysis of Vibrio cholera w/ serum
    • Exp. 1
    • - Normal fresh serum (no immunity) -> no lysis
    • - Immune fresh serum (w/ immunity) -> lysed; Ab?
    • - Heated immune serum -> no lysis
    • - Some heat labile components, in addition to Ab, while is heat stable, are needed to lyse.
    • Exp. 2
    • - Heated immune serum + normal fresh serum -> lysed
    • - Some heat labile sub in normal fresh serum "complements" the Ab to lyse.
    • - Proof of principle
  38. Complement
    • A complex series of proteins
    • Activated in a fixed sequence to non-specifically "complement" the action of Ab
    • When activated, all cleaved into a big and a small fragments (split product)
    • Sequential lysis -> "proteolytic enzymes" for the next
    • The fragments are responsible for their function
    • Attach to microbes or Ab bound to microbes
    • Inhibited by regulatory proteins on host cells
  39. All pathway of complement activation converge on ______.
    • C3
    • Classical, alternative, lectin
  40. Sequence of complement activation
    1, 4, 2, 3, 5-9.
  41. C1 is composed of:
    • C1q: binds to Fc of Ab; hexamer; requires multivalent binding
    • C1r: protease, activates C1s
    • C1s: protease, lyses C4 and C2
    • 750kD in total, heaviest among all complements
  42. C3 has a serum concentration of
    >1mg/ml, highest among all complements
  43. C1q only binds to IgM when it _______ and IgG when it _____.
    • binds to Ag, so the Fc regions of the pentamer are exposed
    • binds to pathogen surface so that there are multiple Fc regions adjacent to each other (from different IgG molecules)
    • Won't activate C1q when freely moving/soluble
  44. Steps of classical pathway of complement activation
    • C1q binds to Fc region of IgG on Ag surface (can be IgM, too), activates C1r -> C1s
    • C4 binds to C1q
    • C4a is cleaved off, C4b stays on C1q or binds of pathogen surface
    • C2 binds to C4 and C1s cleaves C2a off, C4b2b = C3 convertase
    • C3 convertase cleaves C3a off
    • C3b binds to pathogen surface or C4b2b, Cab2b3b = C5 convertase
    • C5a cleaved off, C5b continues.
  45. Small pieces cleaved off from complement
    esp. C3a and C5a, induce inflammatory acute reaction that mimic serious allergic reaction
  46. C3b binds to antigen via __________.
    • thioester linkage
    • thioester concealed inside off C3
    • exposed after cleaving off C3a
    • hydrolyzed/disabled when no microbe available (fluid phase)
    • covalently bonded to surface protein or polysaccharide of microbes
  47. Components involved in alternative passway
    C3, factor B, factor D, Properdin
  48. Alternative pathway of complement activation
    • spontaneous cleavage of C3 -> C3b
    • C3b hydrolysis/disabled in fluid phase
    • C3b binds to pathogen surface
    • factor B binds to C3b-Ag
    • cleavage of B -> Bb
    • C3bBb = C3 convertase, cleavage of more C3; properdin stabilizes C3bBb
    • C3b binds to pathogen surface and C3bBb
    • C3bBb3b = C5 convertase, cleavage of C5 -> C5b
  49. Alternative vs. classical
    • C3 convertase: C3bBb vs C4bC2b
    • C5 convertase: C3bBbC3b vs C4bC2bC3b
  50. Late steps of complement activation
    • C5 convertase cleaves C5->C5b
    • C6,C7 bind to C5b
    • C8 binds to C5bC6C7; integrate to membrane and shows some lysis
    • this complex binds to poly C9 to form MAC (membrane attack complex)
  51. Surface receptors for complements
    • CR1 (CD35) - many cells; phagocytosis, clearance of immune complexes
    • CR2 (CD21) - B cells; corecptors for B cell activation, binds to C3d, cleavage product of C3b
    • CR3 (CD11b/18), CR4 (CD11c/18) - monocytes / macrophages; phagocytosis
  52. C-receptor enhanced phagocytosis by mononuclear phagocyte -
    • opsonization
    • C3b attached to pathogen surface binds to corresponding receptor on phagocyte surface
    • the binding enhances the binding Ag-AbFab-ABFc-FcR
    • promotes phagocytosis
  53. Down-regulators of complement activation
    • prevents inappropriate binding leading to self-destruction
    • C1 INH -> C1r, C1s
    • Factor I + membrane cofactor for protein (MCP, CD46) -> C4b, C3b
    • Decay accelerating factor (DAF) -> C3b convertase
    • CD59 -> C7, C8
  54. _____________ displace C2b from C4b; __________ displace Bb from C3b.
    • DAF, MCP, or CR1
    • DAF or CR1
  55. Biological Functions of Complement
    • Opsonization and Phagocytosis - binding of C3b or C4b to microbe (opsonization), recognition by phagocyte's surface receptor, ingested more efficiently
    • Stimulation of Inflammation - C3a, C5a = anaphylatoxins, recruit & activates leukocytes
    • Complement-mediated Cytolysis - MAC punches a hole on the microbe membrane -> osmotic lysis
    • Immune Clearance (i.e., Solubilization of immune complexes; IC) – important to prevent accumulation in the blood and deposition in vessel walls, which can lead to IC-mediated tissue damage, vasculitis in kidney., via inflammatory cells
    • Trapping of IC in germinal centers – C receptors on Follicular Dendritic Cells bind IC and present antigen to B cells during humoral immune responses.
    • B cell activation – C3d (cleavage product of C3b) binds to CR2 on B cells, providing a signal to initiate B cell activation during humoral immune responses.
  56. Complement Deficiencies
    • Not life-threatening
    • Classical Pathway:
    • - C1q, C1r
    • - C2 (most common) & C4 -- autoimmune diseases (e.g., SLE, systemic leukoerythroblastosis)
    • - C3 -- G(+) infections
    • Alternative Pathway:
    • - Properdin & Factor D -- G(+) infections
    • Membrane Attack Complex (MAC): C5-9 - Neisseria bacterial infections
Author
akhan
ID
320498
Card Set
Oral Immunology - 0518 - L5 6
Description
Oral Immunology - 0518 - L5,6
Updated