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Infection * > S2 Innate Immune System > Flashcards

S2 Innate Immune System Flashcards

1
Q

What are the 3 factors determining the outcome of the host-pathogen relationship? Which part of the infection model does each effect?

A
  • infectivity (pathogen)
  • host’s immune response (patient)
  • virulence (mechanism of infection)
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2
Q

What does infectivity mean?

A

Ability of microbe to establish itself within/on the host

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3
Q

What does virulence mean?

A

Capacity of the microbe to do damage

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4
Q

Which 3 groups are at increased risk of infection?

A
  1. Elderly
  2. Children
  3. Pregnant women
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5
Q

What is the immune system?

A

Cells and organs that contribute to immune defences against infectious and non-infectious conditions (self vs non-self)

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6
Q

What is an example of a non-infectious condition the immune system targets?

A

Cancer

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7
Q

What is an infectious disease?

A

When the pathogen succeeds in evading and/or overwhelming the host’s immune defences

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8
Q

What are the 4 roles of the immune system?

A
  1. Pathogen recognition (cell surface and soluble receptors)
  2. Containing/eliminating the infection (killing and clearance mechanisms)
  3. Regulating itself (minimum damage to host)
  4. Remembering pathogens (preventing reoccurrence of the disease)
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9
Q

What are the two types of immunity?

A
  • innate immunity

* adaptive immunity

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10
Q

What is innate immunity?

A
  • first immunity
  • immediate protection
  • fast (seconds)
  • lack of specificity
  • lack of memory
  • non change in intensity
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11
Q

What is adaptive immunity?

A
  • second immunity, if any pathogen gets through innate
  • long lasting protection
  • slow (days)
  • specificity
  • immunologic memory
  • changes in intensity
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12
Q

What are the first lines of defence?

A

Factors that prevent entry and limit growth of pathogens

  • physical barriers
  • physiological barriers
  • chemical barriers
  • biological barriers
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13
Q

What are the physical barriers?

A
  • skin
  • mucous membranes (mouth, respiratory tract, GI tract, urinary tract)
  • bronchial cilia
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14
Q

What are the physiological barriers? Give an example of an infectious disease that causes each

A
  • diarrhoea (food poisoning)
  • vomiting (hepatitis)
  • coughing (pneumonia)
  • sneezing (sinusitis)
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15
Q

What are the chemical barriers?

A
  • low pH e.g. on skin, in stomach and vagina

* antimicrobial molecules - IgA, lysozyme, mucus, gastric acid and pepsin, beta-defensins

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16
Q

What are the biological barriers?

A
  • normal flora (non-pathogenic microbes) that become pathogenic if get into wrong location
17
Q

What are the benefits of the human microbiome?

A
  • they compete with pathogens for attachment sites and resources
  • produce antimicrobial chemicals
  • synthesis vitamins
  • lead to immune maturation
18
Q

Give examples of some normal flora that inhabit the skin.

A
  • staphylococcus aureus
  • staphylococcus epidermidis
  • streptococcus pyogenes
  • candida albicans
  • clostridium perfingens
19
Q

Give examples of some normal flora that inhabit the nasopharynx.

A
  • streptococcus pneumoniae
  • neisseria meningitidis
  • haemophilius species
20
Q

When do clinical problems arise from normal flora?

A

Displacement of normal flora by e.g. breaching of the skin integrity, fecal-oral route or fecal-perineal-urethral route, poor dental hygiene/dental work, depleted by antibiotic therapy or overgrown and becomes pathogenic

21
Q

Who are high-risk patients to serious infections?

A
  • asplenic patients
  • patients with damaged or prosthetic heart valves
  • patients with previous infective endocarditis
22
Q

What are the second lines of defence?

A

Factors that will contain and clear the infection

  • phagocytes
  • chemicals
  • inflammation
23
Q

What are the 3 main phagocytes?

A
  • macrophages (in all organs) - produce cytokines/chemokines and phagocytose microbes
  • monocytes (in blood) - differentiate into macrophages at infected tissue
  • neutrophils (blood) - increase during infection, recruited by chemokines to infection site
24
Q

What are the other key cells of the innate immunity (minus phagocytes)?

A
  • basophils/mast cells
  • eosinophils
  • natural killer cells
  • dendritic cells - present microbial antigens to T cells (acquired immunity)
25
Q

How do phagocytes recognise microbes?

A

Phagocytes have pathogen recognition receptors (PRRs) e.g. TLR4 that recognise and bind to pathogen-associated molecular patterns (PAMPs) on the microbe

Microbes also have proteins called opsonins on their surface that bind to opsonin receptors on phagocyte

Two attachments increases recognition - more enhanced

26
Q

What are examples of opsonins? Why are they important?

A
  • complement proteins
  • antibodies e.g. IgG
  • acute phase proteins e.g. CRP

Essential in clearing encapsulated bacteria

27
Q

What do phagocytes do?

A

Ingest and destroy (phagocytosis)

28
Q

In which two pathways do phagocytes kill microbes?

A
  • oxygen dependent pathway (respiratory burst) - toxic oxygen products
  • oxygen-independent pathways - enzymes
29
Q

What is the antimicrobial action of C3a and C5a complement serum proteins?

A

Recruitment of phagocytes

30
Q

What is the antimicrobial action of C3b-C4b complement serum proteins?

A

Opsonisation of pathogens

31
Q

What is the antimicrobial action of C5- C9 complement serum proteins?

A

Killing of pathogens

Membrane attack complex

32
Q

What are the 2 activating pathways of complement serum proteins?

A
  • alternative pathway

* MBL pathway

33
Q

What are clinical problems that arise if phagocytosis is reduced?

A
  • decrease spleen function
  • decrease neutrophil number
  • decrease neutrophil function
34
Q

What are the antimicrobial actions of macrophage-derived cytokines like TNFalpha/IL-6/IL-1

A
  • systemic actions - liver (CRP and MBL - complement activation), bone marrow (neutrophil mobilisation), hypothalamus (increased temp)
  • local inflammatory actions - blood vessels (vasodilation, vascular permeability, expression fo adhesion molecule to attract neutrophils)
35
Q

What is the summary of the innate immune response?

A
  1. Innate barrier breached
  2. Complement, mast cells and macrophage activation
  3. Cytokine/chemokine production causes vascular changes and chemoattraction
  4. Hypothalamus and liver cause fever and acute phase response
  5. Redness, heat, swelling and pain due to local inflammation

Infection * (18 decks)

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