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MICR3305 > 23 - Immune Responses to Bacteria > Flashcards

23 - Immune Responses to Bacteria Flashcards

1
Q

Pathogenesis

A
  • Attachment and colonisation to host tissue
  • Invasion into deeper host tissue and production of toxins
  • Growth and multiplication at site of invasion
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2
Q

What determines immune responses to pathogneic bacteria

A

Surface chemistry

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3
Q

What is active against peptidoglycan layer

A

Lysosomal enzymes and lysozymes

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4
Q

What is active against. the outer lipid bilayer of gram negative

A

Cationic proteins and complement

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5
Q

What are immune responses to pathogens determined by

A

-If intracellular or extracellular
- Mechanisms of pathogenicity

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6
Q

Direct mechanisms of tissue damage by pathogens

A
  • Exotoxin production
  • Endotoxin (e.g. LPS)
  • Direct cytopathic effect
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7
Q

Indirect mechanisms of tissue damage by pathogens

A
  • Immune complexes
  • Anti host antibody
  • Cell mediated immunity
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8
Q

Recognition of bacterial components

A
  • Many PAMPS activate cells via TLRs and other PRRs
  • TLR activation leads to expression of co stimulatory molecules on phagocytes and has important role in production of inflammatory cytokines
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9
Q

Nucleotide binding oligomerisation domain (NOD) like receptors

A

Recognise bacterial degradation product in the cytoplasm

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10
Q

Extracellular bacteria

A
  • Replicate outside host cells (e.g. blood, connective tissue) and in tissue spaces
  • Induce inflammation resulting in tissue injury at the site of infection and produce toxins
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11
Q

Immunity to extracellular bacteria

A
  • Phagocytosis, complement activation, and the inflammatory response
  • Humoral immunity is a major protective immune response against extracellular bacteria, and it functions to block infection, to eliminate the microbes, and to neutralise their toxins
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12
Q

Anaphylatoxin C5a

A
  • Enhances the phagocytosis of microorganisms opsonised in an innate immune response
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13
Q

What are phagocytes attracted by

A
  • Bacterial structural components
  • Complement products such as C5a
  • Locally released cytokines and chemokines derived from resident macrophages and epithelial cells
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14
Q

What is neutralisation mediated by

A

High affinity IgG, IgM, and IgA

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15
Q

What is opsonisation mediated by

A

IgG1 and IgG3

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16
Q

What is complement activation initated by

A

IgM, IgG1 and IgG3

17
Q

Cell mediated immune responses to extracellular bacteria

A
  • CD4 + helper T cells induce local inflammation, enhance the phagocytic and microbicidal activities of macrophages and neutrophils, and stimulate antibody production
  • Th17 responses recruit neutrophils and monocytes and promote local inflammation at sites of bacterial infection
18
Q

Intracellular bacteria

A
  • Bacteria that are ingested by macrophages but able to survive and replicate within these cells
  • some infect nonphagocytic cells
  • Can be facultative or obligate intracellular bacteria
19
Q

Immunity to intraceullar bacteria

A
  • The innate immune response to intracellular bacteria is mediated mainly by phagocytes and NK cells
  • The major protective immune response against intracellular bacteria is T cell–mediated recruitment and activation of phagocytes
20
Q

Cytokines that mediate innate immune response to intracellular bacteria

A

Il-12 and IFN-γ

21
Q

M1 macrophages

A
  • Classically activated macrophages
  • Microbicidal and inflammation
  • induced to differentiate by IFN gamma and CD40L
22
Q

M2 macrophages

A
  • Alternatively activated macrophages
  • Anti inflammatory effects, wound repair
23
Q

IFN-γ and TNF-α, produced by Th1 cells, and CD40:CD40L interaction

A

Contribute to the recruitment of monocytes and granulocytes and
activate the anti-microbial activity of macrophages through phagosome maturation, production of reactive nitrogen intermediates and antigen presentation

24
Q

Mechanisms used by bacteria to subvert the host immune system

A
  • Inhibition of PAMP recognition
  • Antigenic variation
  • Inhibition of opsonisation
  • Resistance to antimicrobial peptides
  • Phagocytosis inhibitions
25
Q

Mechanisms used by Neisseria
gonorrhoea to evade humoral immunity

A
  • Fails to evoke a large antibody response
  • Secretes an IgA protease to destroy antibody
  • Membrane vesicles (blebs) are released (deplete antibody levels)
  • Alter antigenic composition (e.g. LPS may be sialylated)
26
Q

Th1 Effector functions in infections by intracellular bacteria

A
  • Induce and activate M1 macrophages
  • Induce apoptosis of bacteria laden macrophages
  • Act on naive CD4 and CD8 cells to favour production of Th1
  • Stimulate production of monocytes by bone marrow
  • Acts on endothelium to enhance macrophage exit from blood vessel
  • Produces CCL2, a chemoattractant for monocytes

MICR3305 (25 decks)

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