Immuno: Phagocytosis, Inflammation

Question 1

describe PAMPs (pathogen associated molecular patterns)

Answer 1

• essential to microbial survival and metabolism which makes them relatively invariant and evolutionary stable
• examples:
  
  • peptidoglycan found in bacterial cell walls
  • flagellin, a protein found in bacterial flagella
  • LPS from the outer membrane of gram-negative bacteria
  • lipopeptides, molecules expressed by most bacteria
  • nucleic acids such as viral ds RNA

Question 2

which toll like receptors (TLRs) are associated with viruses?

Answer 2

TLR 3, 7, 8, 9

Question 3

describe opsonization

Answer 3

• addition of an opsonin, to ensure cell is readily identified, and more efficiently taken by phagocytes (enhance phagocytosis)
• phagocytes have specific receptors for this mechanism:
  
  • CR1 - complement receptor for C3b fragment (complement cascade)
  • Fc receptors for Fc region of immunoglobulins (antibodies)

Question 4

describe the opsonins

Answer 4

• antibodies: opsonize the antigen
  
  • Fc region of antibody binds to phagocytic cell receptors
  • phagocytic cells do not have Fc receptors for IgM but IgM activates complement to do the opsonization
  • main opsonin: IgG
• complement molecules: opsonize the antigen
  
  • opsonized antigen binds to CR1 receptor on the phagocyte
  • main opsonins: C3b, C4b and C1q
• circulating proteins (secreted pattern recognition receptors): pentraxins, ficolins, collectins (Mannose-binding lectin, MBL)

Question 5

describe the mechanism of phagocytic recognition, engulfment and killing

Answer 5

• chemotaxis and ingestion: phagocytes migrate and recognize PAMPs that drive initiation and perpetuation of the inflammatory response
• phagolysosome formation: lysosome fused with phagosome (death ~30 min)
• destruction and elimination:
  
  • oxygen-dependent system (respiratory burst)
  • liberation of lactic acid, lysozyme and nitric oxide

Question 6

describe oxygen-independent phagocytic killing

Answer 6

• lysozyme: split peptidoglycan
• lactoferrin and reactive nitrogen intermediates: deprive pathogens of iron
• proteolytic enzymes: degrade dead microbes
• defensins, cathepsin G and cationic proteins: damage microbial membrane

Question 7

describe oxygen-dependent degradation (oxidative burst)

Answer 7

• NADPH oxidase produces superoxide which recombines with other molecules to produce reactive free radicals
• the superoxide reacts with NO forming peroxynitrate
• myeloperoxidase uses the derived H2O2 to produce hypochlorite (antimicrobial)
• to combat infxns, immune cells use NADPH oxidase
• absence of NADPH oxidase will prevent the formation of ROS and resulti n chronic granulomatous disease (CGD)

Question 8

describe lab tests for CGD

Answer 8

• the nitroblue-tetrazolium (NBT) test
• the higher the blue socre, the better the cell is at producing ROS
• in CGD, the test will be negative

Question 9

describe Chediak-Higashi syndrome

Answer 9

• autosomal recessive disorder that arises from a mutation of a lysosomal trafficking regulator protein
• the disease is characterized by large lysosome vesicles in phagocytes with poor killing action leading to:
  
  • susceptibility to infxns
  • abnormalities in nuclear structure of leukocyte
  • anemias
  • hepatomegaly
  • Dohle bodies (cytoplasmic inclusions in neutrophils)
• clinical presentation: albinism, neutropenia, periodontal disease, recurrent infxns

Question 10

describe the steps of the inflammatory response

Answer 10

• injury/immediate rxns:
  
  • injury/damage causes release of chemical mediators, cytokines, histamine
  • attracts leukocytes to the site of injury
• vascular reactions:
  
  • histamine causes vasodilation, increased vessel permeability (redness and heat)
  • delivers leukocytes, fluid and clotting factors to the site of injury
• edema and pus formation:
  
  • edema (swelling) helps contain the infxns and attract neutrophils
  • debris and WBCs form pus
  • bradykinin stimulates pain receptors

Question 11

summarize the mediators of acute inflammation

Answer 11

Question 12

describe the cell adhesion molecules (CAMs)

Answer 12

• selectins
  
  • glycoproteins
  • bind to carbohydrates
  • expressed on leukocytes and endothelial cells
• mucins
  
  • proteins
  • present CHO ligands to selectins
  • present on endothelial cells and neutrophils
• integrins
  
  • proteins; heterodimers
  • expressed on leukocytes
  • bind to Ig superfamily molecules
• ICAMs
  
  • Ig CAMs
  • expressed on endothelial cells
  • bind to integrins

Question 13

describe the 4 steps of leukocyte extravasation

Answer 13

• rolling
  
  • mediated by binding of selectins (endothelium) to mucin-like CAMs (leukocyte)
• activation
  
  • chemokine binding induces conformational change in integrins (leukocyte)
• arrest/adhesion
  
  • integrins now capable of binding Ig-superfamily CAMS (endothelium)
• transendothelial migration
  
  • migration through tight junctions of inflamed endothelium

Question 14

describe leukocyte adhesion defect (LAD)

Answer 14

• patients with LAD1 have an inherited defect that causes a deficiency of the B-2 integrin subunit (CD18)
  
  • this subunit is involved in the formation fo the B-2 integrins by dimerization with different CD11 subunits
• the main function of these proteins is to allow neutrophiles to make their way out of the blood stream by adhering to the different ligand ICAM-1
• in LAD1 patients, neutrophils cannot extravasate and fight against bacteria in tissues

Question 15

describe the Kinin system (mediator of inflammation)

Answer 15

• Hagman factor (XII) activation leads to bradykinin formation
  
  • increased vasodilation, permeability, pain and smooth muscle contraction

Question 16

describe the clotting system (mediator of inflammation)

Answer 16

• Hagman factor activation leads to increased thrombin and clot formation that stops bleeding
• forms a fibrinous meshwork at an injured or inflamed site
  
  • prevents the spread of infxn and keeps microbes at the site of inflammatory cell activity
  • provides a framework for repair and healing
  • main substance: fibrin

Question 17

describe the fibrinolytic system (mediator of inflammation)

Answer 17

• Hagman factor activation leads to plasmin activation
• Plasmin breaks down clots and activates complement

Question 18

describe the complement system (mediator of inflammation)

Answer 18

• anaphylatoxins activate mast cells, which increase permeability

Question 19

describe the early events of the inflammatory process

Answer 19

• acute inflammation
  
  • increased E-selectin and P-selectin on endothelium
    
    • due to thrombin, histamine, IL-1, TNFa
  • attachment of circulating neutrophils
  • transendothelial migration
• infiltration of neutrophils
  
  • chemotaxis
    
    • IL-8, leukotriene B4, C5a, fibrinopeptides act as chemokines
• phagocytosis
  
  • increased Fc receptor expression, complement receptors, stimulation of cytotoxic compounds (free radicals)

Question 20

describe the localized events of the inflammatory process

Answer 20

• vasodilation
  
  • bradykinin
• vascular permeability
  
  • bradykinin, fibrin breakdown, histamine
• neutrophils release chemokines
  
  • chemoattractant for macrophages
  • macrophages arrive 5-6 hours after inflammation begins
• activated tissue macrophages
  
  • secrete IL-1, IL-6, TNFa

Question 21

describe the systemic acute phase response of the inflammatory process

Answer 21

• mediated by IL-1, IL-6, TNFa
  
  • act on hypothalamus: fever
  • act on liver: increase acute phase proteins
  • act on bone marrow: increase leukocytosis
• increased acute phase proteins
  
  • C-reactive protein, fibrinogen, haptoglobin, amyloid, ceruloplasmin
  • activates complement
• increase leukocytosis
• left shift, increase in immature cells (bands)

Question 22

describe the chronic inflammatory response

Answer 22

• inflammation lasting 2 weeks or longer
• often related to an unsuccessful acute inflammatory response
• IFNγ and TNFa play a major role