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BIO388 - MOLECULAR AND CELLULAR IMMUNOLOGY > Cellular innate immunity > Flashcards

Cellular innate immunity Flashcards

1
Q

What are the phagocytic cells in innate immunity?

A

Neutrophils, dendritic cells and macrophages.

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2
Q

Do non-phagocytic cells show phagocytosis?

A

Yes, there is some evidence of them phagocytosing pathogens, although this is not their main role.

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3
Q

What are the main differences between innate and adaptive immunity?

A

Speed:
- Adaptive is slow (days), innate is fast (minutes-hours).

Evolution:
- Adaptive is found only invertebrates, innate is evolutionarily old.

Specificity:
- Adaptive is highly specific, innate is relatively non-specific.

Memory:

  • Adaptive has a highly specific memory, innate has no specific memory.
  • > However, there is evidence showing some memory in macrophages.

Driver:
- Adaptive is driven by lymphoid cells, innate is mostly driven by myeloid cells.

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4
Q

Describe the general differentiation to innate immunity cells.

A
  1. Pluripotent haematopoietic stem cell (bone marrow).
  2. Common myeloid progenitor (bone marrow).
  3. Granulocyte/macrophage progenitor (bone marrow).
  4. Innate cells (blood).
  5. Innate cells (tissue).
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5
Q

Which innate cells are mature in the blood?

A

Neutrophils, eosinophils, basophils.

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6
Q

Which innate cells mature in the tissues?

A

Mast cells (only found in tissues, not blood) and macrophages.

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7
Q

What innate cell precursor is in the blood?

A

Unknown precursor of mast cell.

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8
Q

What are monocytes and where are they found?

A

Immature precursors of macrophages, found in the blood.

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9
Q

Which 2 innate cells are the exception to the general pathway and why?

A
  1. Dendritic cells.
    Some of these have lymphoid progenitors (adaptive cells). However, mostly come from the myeloid monocyte progenitor.
  2. Natural killer cells.
    These are considered as innate cells, despite differentiating from a lymphoid progenitor (adaptive).
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10
Q

Where are dendritic cells mature?

A

Lymph nodes.

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11
Q

What is the differentiation pathway of a natural killer cell?

A
  1. Pluripotent haematopoietic stem cell (bone marrow).
  2. Common lymphoid progenitor (bone marrow).
  3. NK cell (blood).
  4. NK cell (lymph nodes).
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12
Q

What is the function of macrophages and how do they move?

A
  • To tackle the primary infection and raise the alarm.
  • They act as antigen presenting cells: they phagocytose the pathogen, process it and present it to T and B cells.
  • The main cell body remains static and they put out ‘fingers’ which move.
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13
Q

Where are macrophages found and what is the importance of this?

A

In the tissue. They also mature here. Macrophages specialise dependant on the tissue to allow for easier encountering of the pathogen.

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14
Q

What are the differences between tissue-specific macrophages? Give an example of different types.

A

They have different morphologies and cell surface markers.

  • Alveolar macrophages have CD11c, CD64.
  • Microglia have CD11b and CD45, CD68.
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15
Q

When do macrophages encounter a pathogen?

A

First, as they are in the tissue.

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16
Q

How do macrophages recognise foreign particles?

A
  • PAMPs (endogenous ligands on the pathogen surface).

- Opsonins (host factors that are deposited onto the surface).

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17
Q

What is an experiment that can be done to see how macrophages phagocytose?

A

Expose them to latex beads - these are foreign particles but are inert so don’t stimulate the immune system.

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18
Q

What is a difficulty found when studying macrophages and how is it resolved?

A

They are very dynamic.
Resolved by ‘pinning’ them down.
- OVA-TRITC+IgG is put in ordered dots on a slide. Ovalbumin is a non-self antigen and it is stained. IgG is used so the macrophages can bind.
- The macrophage tries to phagocytose the dots and spreads out and becomes flat.
- The dots can’t be phagocytosed, instead they keep the macrophage in place, acting as an anchor.

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19
Q

How do macrophages raise the alarm?

A
  • They release cytokines (a secreted protein which affects a nearby cell and signals it to do something immune-related).
  • They release chemokines (protein that triggers chemotaxis in cells. They also recruit other cells).
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20
Q

Describe the events following cytokine and chemokine release.

A
  1. Vasodilation and pain is seen as macrophages are recruited.
  2. Increased fluid brings in humoral components (the complement system).
  3. Neutrophils migrate into the tissue by changing of the endothelial cell surface to allow it to stick-roll-enter.
  4. T cells enter the tissue.
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21
Q

What are the main functions of dendritic cells?

A
  • To phagocytose and destroy pathogens.
  • To link innate and adaptive immunity, by being the major antigen presenting cell.
  • To carry out macropinocytosis (engulf extracellular fluids) constitutively.
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22
Q

What happens when a dendritic cell encounters a pathogenic antigen?

A

Antigen presenting occurs (it is processed and expressed on the cell surface via MHC proteins).
They then leave the tissue and enter the lymph nodes. Here, they present the antigen to T cells and activate them.

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23
Q

How do dendritic cells move?

A

They have long cytoplasmic extensions (‘dendrites’) which move rapidly, these cause the whole cell to move at a moderate speed/

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24
Q

Name some different subtypes of dendritic cells and their location/function.

A

CD103+
These migrate to lymph nodes for antigen presentation.
- Behave as normal DCs.
- Found to have a key role in proliferation of Treg cells within gut tolerance.

CD103-
These remain in the tissue and promote local T-cell and inflammatory responses.
- Behave as macrophages.

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25
Q

How can neutrophils be distinguished under a microscope?

A

They have multi-lobed nuclei.

26
Q

Describe the lifespan and movement of neutrophils.

A

Very fast moving.

Short lived; live for 1-2 days.

27
Q

What is the function of neutrophils?

A

They migrate rapidly to the site of infection once cytokines and chemokines are released. Here, they phagocytose the pathogen and then self-destruct.

28
Q

When do neutrophils encounter a pathogen and why?

A

~2 hours into the immune response as they are not tissue resident, they are found in the blood.

29
Q

What % of the circulating WBCs do neutrophils make up?

A

70%

30
Q

What is an emerging function of neutrophils and why?

A

Are involved in resolving inflammation.

- As they self destruct, they release many molecules, including pro-inflammatory molecules in the tissue.

31
Q

Name some chemoattractants which attract neutrophils.

A
  • C5a (from the complement system).
  • IL-8
  • IFNgamma
  • ATP
32
Q

What other cells are phagocytes in humans and in bony fish?

A

Humans:

  • Gamma-delta T cell.
  • Some granulocytes.

Bony fish and Xenopus:
- B-cells.

33
Q

Name a disease which arises due to neutrophil defects?

What happens in this disease?

A

Chronic granulomatous disease.

  • Caused by mutations in the PHOX genes.
  • Means that NADH complexes don’t form in the phagosome. These are required to pump ROS in, which allows for self-destruction.
  • > In this disease, phagocytosis can occur but the neutrophils aren’t killed.
  • > Therefore, the patient is highly susceptible to infection even by non-infectious organisms.
  • > Patients usually die before adulthood.
34
Q

What are the non-phagocytic cells in innate immunity?

A

Eosinophils, basophils, mast cells and natural killer cells.

35
Q

Describe the morphology and proportion of eosinophils.

A

Make up 1% of WBCs.
Have a horseshoe nucleus.
Have cytoplasmic granules which have glutamate in. This attracts the positive dye eosin (=name).

36
Q

Describe the morphology and proportion of basophils.

A

Make up 3% of WBCs.

Have a horseshoe, bi-lobed nucleus.

37
Q

How did eosinophils get their name?

A

They have many cytoplasmic granules which contain glutamate.
The glutamate is acidic and attracts the dye eosin which is basic. Therefore, the granules appear red under a microscope.

38
Q

What is the main function of eosinophils?

A

To kill pathogens which are too large to phagocytose, e.g. parasitic worms.
They do this by releasing their granules which contain a range of toxins and enzymes in response to an antibody-coated pathogen.

39
Q

Which antibody do eosinophils particularly recognise?

A

IgE

40
Q

In which group of animals are eosinophils found?

A

Vertebrates and invertebrates.

- Not clear how they work in invertebrates.

41
Q

How do eosinophils activate local tissues to have an immune response?

A

By releasing cytokines.

42
Q

What is known about basophils?

A

Not much.

They contain a range of toxins/enzymes and are often found close to internal or exo- parasites.

43
Q

What is the main known function of basophils?

A

In IgE mediated allergic reactions.

- They secrete many cytokines including IL-4.

44
Q

What is a controversial function of basophils?

A

If they play a role in Th2 antigen presentation.

45
Q

What is the function of mast cells?

A

To release granules containing histamine and active agents in response to IgE.
They have a major role in allergic responses, where they react with the allergen and release inflammatory mediators.

46
Q

What is the tissue effect of mast cells?

A

Cause host tissue damage.

47
Q

What other cells are mast cells closely linked to?

A

Basophils and eosinophils.

- Cross-talk occurs and they act upon each other to cause a larger immune response.

48
Q

Name the different classes of agents released upon granulation of mast cells.

A

Enzymes, toxic mediators, cytokines, chemokines and lipid mediators.

49
Q

Give an example of an enzyme released by mast cells and the biological effect it has.

A

Tryptase, remodels the connective tissue matrix.

50
Q

Give an example of a toxic mediator released by mast cells and the biological effect it has.

A

Histamine, causes smooth muscle contraction, increases vascular permeability and kills parasites.

51
Q

Give 3 examples of cytokines released by mast cells and the biological effect they have.

A

IL-4: stimulates and amplifies the Th2 response (adaptive).
IL-3: promotes eosinophil production and activation.
TNF-alpha: promotes inflammation, stimulates other cells to produce cytokines and activates the endothelium.

52
Q

Give an example of a chemokine released by mast cells and the biological effect it has.

A

CCL3, attracts monocytes, macrophages and neutrophils.

53
Q

Give an example of a lipid mediator released by mast cells and the biological effect it has.

A

Prostaglandin D2, causes smooth muscle contraction, increases vascular permeability and stimulates mucus secretion.

54
Q

Where are mast cells present?

A

All of the body’s surfaces.

55
Q

How do mast cells work?

A

Constitutively bind IgE which triggers cytokine and chemokine release. This causes inflammation.

56
Q

Why are natural killer (NK) cells unusual?

A

They are lymphoid but are not pattern antigen specific.

- This means they behave as an innate cell despite coming from an adaptive progenitor.

57
Q

How do NK cells kill pathogens?

A

They release toxic granules and induce apoptosis in the host cell.

58
Q

How do NK cells recognise infected cells?

A

Look for abnormalities in the host cells protein surface receptors.

59
Q

What do inflammatory cytokines do?

A

Increase vascular diameter, activate endothelial cells and attract leukocytes.
- Leukocytes then extravate at the site of infection and blood clotting occurs.

60
Q

Describe endothelial activation and its purpose.

A

When cytokines are released, endothelial cells express different adhesion molecules on their surface, e.g. selectins.
These grab passing neutrophils and cause them to slow down and roll on the membrane.
During this, bonds are formed and broken between selectins and the ligand.
Chemokines cause integrins on the endothelial cell to bind tightly to neutrophils, immobilising them.
Now, the neutrophil is able to extravate into the tissue and reach the site of infection via changes in the cytoskeleton.

61
Q

What is a debated function of neutrophils?

A

Extracellular trapping.
This is when the neutrophil forms a trap made out of extracellular fibres which bind to pathogens. This allows the neutrophil to sacrifices itself and releases its content to every neighbouring pathogen, minimising host cell damage.
It is not known is this occurs in vivo.

62
Q

Summarise the innate defences

A
  • Constitutive defences (barriers, defensins)
  • Macrophages (first line of attack)
  • Neutrophils (main attack)
  • DCs (primary APC)
  • NK cells (hybrid adaptive/innate cell)
  • Mast cells (local inflammation)
  • Eosinophils and basophils (extracellular destruction)

BIO388 - MOLECULAR AND CELLULAR IMMUNOLOGY (14 decks)

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