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Immunology > Review of the innate immune system > Flashcards

Review of the innate immune system Flashcards

1
Q

What does a resolution of infection require?

A

• Resolution of infection requires both adaptive and innate immune responses

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2
Q

What does adaptive immunity involve?

A

Involves very specific recognition of infectious agent (usually sees a protein = antigen)

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3
Q

What is there no specific recognition in innate immunity and what does it involve?

A

• Innate immunity – no specific antigen recognition

§ Innate involves recognition of broadly conserved features of different classes of pathogens

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4
Q

What are the components of the innate immune system?

A

• Phagocytosis
• The Inflammatory Response
• Cytokines, Interferons and Antimicrobial peptides (AMPs)
• Complement
○ Enhances ability of immune system to work
• Intrinsic Defences – “the hostile cell”
• NK cells

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5
Q

What is phagocytosis carried out by in vertebrates?

A

Carried out in vertebrates by dendritic cells, macrophages and neutrophils

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6
Q

What are macrophages never involved in?

A

○ Macrophages are never involved in triggering new immune response but can reactivate memory

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7
Q

Where are macrophages found?

A

Macrophages are tissue-resident

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8
Q

What cells do most of the phagocytosing?

A

Neutrophils do most of the phagocytosing

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9
Q

What does phagocytosis clear and present and what does this promote?

A

• Phagocytosis clears pathogens but also presents peptides on MHCs – this promotes development or reactivation of the adaptive immune response
§ Selects and stimulates division of naïve T and B cells

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10
Q

What are the 2 distinct roles of macrophages in innate immunity?

A
  1. Phagocytosis; material is destroyed in lysosomes

2. Captured material can trigger macrophage activation

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11
Q

What do activated macrophages produce and what does this trigger?

A

○ Activated macrophages produce cytokines and chemokines to stimulate both innate and adaptive immune responses
§ This triggers the inflammatory response and can promote a local anti-microbial state

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12
Q

What is the inflammatory response?

A

A generic defence mechanism whose purpose is to localize and eliminate injurious agents and to remove damaged tissue components

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13
Q

What does the inflammatory response localise?

A

Localizes the infection

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14
Q

What does the inflammatory response remove and repair?

A
  • Removes infectious agent i.e. by phagocytosis

* Repairs tissue damage

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15
Q

What does the inflammatory response enhance?

A

Enhanced permeability, extravasation, cell adhesion and clotting

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16
Q

What does the inflammatory response recruit?

A

• Neutrophil recruitment

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17
Q

What are cytokines and chemokines?

A

Glycoprotein hormones that affect the immune response

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18
Q

What do cytokines act as?

A

○ Act as a very specific signal for a component of the immune system

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19
Q

What does the role of cytokines help?

A

○ Very defined narrow role that helps the immune system

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20
Q

What do cytokines act to modify?

A

○ Act to modify the behaviour of cells in the immune response

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21
Q

What are most of the cytokines called?

A

○ Most of these are called interleukins (eg. IL-1)

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22
Q

Where are chemokines secreted?

A

○ Secreted at site of infection

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23
Q

What do chemokines act as and create?

A

○ Act as chemotactic factors
§ Create concentration gradients which attract (or occasionally repel) specific cell types to a site of production/infection

24
Q

How do pathogens recognise material to ingest?

A

○ By detecting phosphatidylserine on exterior membrane surface (cells undergoing apoptosis)
○ By Scavenger receptors
○ By some Toll-Like Receptors (TLRs)
○ By passive sampling

25
Q

What can passive sampling be done by?

A

§ Done by neurophils

26
Q

Why does passive sampling need to be controlled?

A

§ Can do a lot of tissue damage so need to be controlled

27
Q

What are PAMPs and where they present?

A

• Molecules present only on pathogens and not on host cells

28
Q

What are PAMPs essential for?

A

• Essential for survival of pathogens

29
Q

What are examples of PAMPs?

A

○ Gram-negative bacteria; lipopolysaccharides (LPSs) found in outer membrane
○ Gram-positive bacteria; teichoic acid, lipoteichoic acid, peptidoglycan found in outer membrane
○ Bacterial flagellin
○ Abnormal protein glycosylation
○ Abnormal nucleic acids - viruses

30
Q

What are PRRs?

A

• Host factors that specifically recognise a particular type of PAMP

31
Q

What do extracellular PRRs do?

A

they recognise PAMPs outside of a cell and trigger a co-ordinated response to the pathogen

32
Q

What do intracellular PRRs do?

A

they recognise PAMPs inside a cell and act to co-ordinate a response to the pathogen

33
Q

What do secreted PRRs do?

A

they act to tag circulating pathogens for elimination

34
Q

What is the complement system originally described as?

A

Originally described as a heat-sensitive component of serum that could augment the ability of antibodies to inactivate antigen

35
Q

What does the complement system lead to and how?

A

○ Opsonisation

§ Complement gets recruited and forms a hard shell complement protein around the pathogen

36
Q

What does opsonization make harder?

A

§ Opsonisation makes it hard for the pathogen to exert its effects as it cannot bind to its receptor

37
Q

What do complement proteins act as and what can they be activated by?

A

Complement proteins act as secreted Pattern recognition receptors (PRRs) and can be activated by a range of PAMPs, and can also be activated by “altered self”

38
Q

Classical pathway of complement system

A

○ Works through antigen-antibody pathway

○ Triggering protein C1Q in classical pathway and this recognizes polysaccharides

39
Q

Lectin pathway of complement system

A

○ There to recognise abnormal glycosylation of proteins

○ Any abnormally glycosylated pathogen will attract the lectin pathway of complement system

40
Q

Alternative pathway of complement system

A

○ Any pathogen surface which is not of host origin

41
Q

What are interferons?

A

Secreted factors (type I and type III)

42
Q

What are interferons induced by?

A

Induced by viral infection

43
Q

What are interferons secreted by?

A

Secreted by proteins

44
Q

How does the interferon system work?

A

§ Interferon is produced during primary infection
§ Interferon binds to neighbouring cells that have the receptor for it
§ Triggers antiviral state in neighbouring cells

45
Q

What are defensins?

A
  • Anti-microbial peptides

- Secreted short pepitdes about 18-45 amino acids long

46
Q

How do defensins work?

A

• Usually work by disrupting cell wall leading to lysis

47
Q

What are defensins induced by?

A

• Some are induced by bacterial infection

48
Q

What are example of intrinsic defences?

A 
○ Apoptosis
○ Restriction factors/Intrinsic Immunity
○ Epigenetic silencing
○ RNA silencing
○ Autophagy/Xenophagy
49
Q

What are natural killer cells?

A

Large granular lymphocytes

50
Q

What percentage of WBC’s are natural killer cells

A

• 4% white blood cells

51
Q

What do natural killer cells kill?

A

• Kill certain tumour & virally infected cells

52
Q

What do natural killer cells target?

A

• Target cell destruction is caused by cytotoxic molecules called granzymes & perforins

53
Q

What are natural killer cells activated by?

A

• Activated by loss-of-self

54
Q

What ability do natural killer cells possess?

A

• NK cells possess the ability to recognise and lyse virally infected cells and certain tumour cells.

55
Q

Why do natural killer cells not kill uninfected cells?

A

• NK cells do not kill uninfected cells because they recognize the MHC-peptide complex as well as the fact that there is no activating ligand
§ This is an inhibitory signal so stops NK from targeting healthy/unifected cells

56
Q

Why do pathogens try and downregulate MHC class 1 and what do the natural killer cells do in response?

A 
• Pathogens try and downregulate MHC class I because if it is downregulated, the antigens will not be presented
§ NK cells however, detect the absence of MHC and as there is no inhibitory signal, they lyse the cells by injecting perforins
57
Q

INNATE VS ADAPTIVE

A

CHECK NOTES

Immunology (8 decks)

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