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Infection And Immunity > Killing by Phagocytes > Flashcards

Killing by Phagocytes Flashcards

1
Q

explain Intracellular Bacterial Killing

A
  1. Phagosome
  2. oxygen independent by lysosomal enzymes
  3. Oxygen dependent killing by NO and Reactive Oxygen Intermediates
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2
Q

what are the Two main types of Lysosomes in Neutrophils?

A 
Specific granules (Specific to mature neutrophils)
Azurophil granules
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3
Q

what are Specific granules ?

A
  • made late in PMN development
  • Contain alkaline phosphatase, lysozyme, and lactoferrin
  • Function best at neutral or alkaline pH
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4
Q

what are Azurophil granules?

A
  • made early in PMN development
  • Contain peroxidase, and the”acid hydrolase” enzymes, defensins, also lysozyme
  • Most have pH optima of pH4.5 and lower
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5
Q

who discovered Sequential fusing of different lysosomes is linked to the pH optima of their contents?

A

Dorothy F. Bainton, 1973

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6
Q

what is the pH optima of Specific granules?

A
  • Function best at neutral or alkaline pH
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7
Q

what is the pH optima of Azurophil granules?

A
  • pH optima 4.5 or lower
  • e.g. peroxidase, ”acid hydrolase” enzymes, lysozyme,
  • Azurophilic granules fuse with phagosomes later
  • pH of phagocytic vacuoles drops to 6.5 within 3 min and to 4 within 7–15 min.
  • The pH drop is due to a proton pump (V Type H+ ATPase) in the azurophilic membrane
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8
Q

what is Oxygen independent killing?

A

Destruction of microbes by lysosomal contents, i.e:

1) Anti-microbial peptides
2) Enzymes
3) Nutrient starvation (prevention of growth)

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9
Q

name 2 Lysosomal anti-microbial peptides

A

Defensives and Bactericidal permeability increasing protein (BPI)

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10
Q

what are Defensins?

A 
4 types
Highly cationic (+ve charge) peptides/proteins
Adhere to -ve charged bacterial cell membranes and punch holes
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11
Q

what are BPIs?

A

Highly cationic

Binds Gram -ve bacteria (via LPS)

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12
Q

name the 2 types of Lysosomal enzymes

A

Lysozyme and “Acid Hydrolases”

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13
Q

what the action of Lysozyme?

A
  • Splits peptidoglycan in bacterial cell walls
  • Constitutively expressed by macrophages
  • Stored in lysosomes and secreted
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14
Q

name 4 Acid Hydrolases?

A

Proteases
DNAses
Lipases
Glycopeptideases

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15
Q

what do acid hydrolases do?

A

Digest dead organisms

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16
Q

name 2 Lysosomal nutrient binding proteins

A

Lactoferrin- Deprives proliferating bacteria of iron

Vitamin B12 binding protein- Deprives proliferating bacteria of cobalt

17
Q

what do Lysosomal nutrient binding proteins do?

A

Bind growth limiting metal ions required for microbial enzyme functionality

18
Q

describe Oxygen-dependent killing

A
  1. Enzymes add electrons to oxygen to make radical “Superoxide”
  2. Enzymes react to form Reactive Oxygen Species (ROS)
19
Q

what are Free Radicals?

A
  • a cluster of atoms, one of which contains an unpaired electron in its outermost shell of electrons.
  • extremely unstable configuration, and radicals quickly react with other molecules or radicals to achieve a stable configuration
20
Q

what is NADPH?

A
  • an electron carrier.
  • molecule exists in two forms that vary in whether or not they are carrying electrons.
  • NADPH is the reduced form
21
Q

what does NADPH oxidase do?

A
  1. assembly stimulated by microbes
  2. produces oxygen radicals inside the phagolysosome
  3. converts o2 to superoxide o2-
  4. 2nd enzyme superoxide dismutase convert superoxide to hydrogen peroxide.
  5. peroxidase enzymes and Fe convert h2o2 to hypochlorite ions and hydroxyl ions.
22
Q

what is the affect of Hypochlorous acid and chloramines?

A
  • increase bactericidal power of ROI system by destroying biologically important proteins through chlorination and bromination.
23
Q

what are Myeloperoxidases

A
  • MPO is not found in macrophages, which lose MPO within 2 days of entering the tissues.
  • MPO synthesized during promyelocyte stage, prior to final granulocyte/ monocyte commitment.
  • Peroxidases contain iron in haem-like groups, which means neutrophils or e.g. nasal mucus containing them appear green
24
Q

how does OH (hydroxyl radical) cause damage?

A
  • short-lived, powerful oxidant with high antibacterial activity, causing damage to DNA, membrane lipids, and proteins.
  • hydroxyl radical is most reactive radical known.
  • can attack and damage every molecule found in living cells
25
Q

what is the “Washing machine” analogy

A
  1. Alkaline cycle
    Lysozyme
2. Acid cycle
	Enzymes (protease, lipase, glycopeptidase, DNAse)
	Detergent (cationic peptides)
	Superoxide, Hydrogen Peroxide
	Hydroxyl Radicals, Singlet oxygen
	Bleach (Hyperchlorous acid)
	Nitric oxide
26
Q

what are Reactive Nitrogen Species

A
  • principal RNI is nitric oxide (NO) derived from terminal guanidino-nitrogen atom of L-arginine.
  • reaction catalyzed by inducible form of nitric oxide synthase (iNOS), leading to formation of NO.
27
Q

what up-regulate iNOS

A

Microbes and Interferon gamma

28
Q

what are the Oxygen-dependent killing pathways?

A

Parallel and interacting metabolic pathways generate reactive oxygen intermediates (*ROI) and nitrogen intermediates in phagocytes

29
Q

Summarise phagocyte killing mechanisms

A
  1. Acidification- bactericidal/static
  2. toxic o2 derived- o2-, H2O2, 1o2, OH, OCL-
  3. toxic nitrogen oxides- NO
  4. AMP- defusing
  5. Enzyme- lysozyme and acid hydrolases
  6. competitors- lactorferin
30
Q

summarise Oxygen independent killing

A
  1. Fusion with lysosomes
    Defensins
    Degradative enzymes e.g., lysozyme, proteases
    Binding of metal cations
  2. Late phagosomal membranes contain ATPases that pump protons into vacuole (pH ~ 4)
  3. Lower pH activates acid hydrolase enzymes
31
Q

summarise Oxygen dependent Respiratory Burst killing

A
  1. Activated following phagocytosis
  2. Stimulated by Pathogen Recognition Receptors
  3. Requires increased oxygen consumption
  4. Produces substances that are directly toxic to the bacteria
32
Q

what are the substances directly toxic to bacteria?

A
  • Oxygen-derived products
    O2-, H2O2 , Hydroxyl radicals (. OH)
  • Nitrogen-derived products
    NO (nitrogen oxide)
    Produced by inducible NO synthase (iNOS) enzyme
    Enzyme is induced by cytokines (Interferon )
33
Q

name a Respiratory burst deficiencies

A

chronic granulomatous disease

Infection And Immunity (16 decks)

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