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second line of defence Flashcards

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1
Q

what is the second line of defence?

A

second line of defence are the molecules and cells that pathogens face after breaching the first line of defence

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2
Q

why is the second line of defence important?

A

the second line of defence is vital for the survival of an organism because it can take days for the adaptive immune response to be activated. Even if they are unable to eliminate the pathogen, it keeps infections under control until adaptive immune response kicks in.

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3
Q

when is the second line of defence activated?

A

it is activated when a pathogen has breached first line of defence

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4
Q

what are the characteristics of the second line of defence?

A
  1. non-specific: same response regardless of the type of pathogen
  2. rapid: occurs within minutes to hours of the pathogen invading host
  3. fixed response
  4. no immunological memory: response isn’t larger or faster upon pathogen’s reinfection
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5
Q

what are the specialised cell types in the second line of defence?

A
  • inflammatory
  • phagocytic
  • cytotoxic
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6
Q

what are the molecules that are part of the second line of defence?

A

interferons, cytokines and histamine, complement proteins

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7
Q

what are leukocytes and what are the types of leukocytes?

A

leukocytes are also known as white blood cells and are a group of blood cells that are responsible for protecting the body against pathogens and foreign material. The types of white blood cells include: mast cells, neutrophils, natural killer cells, dendritic cells and macrophages

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8
Q

what are the types of inflammatory cells?

A

mast cells

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9
Q

what are the types of phagocytic cells?

A

macrophages, neutrophils and dendritic cells

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10
Q

what are the types of cytotoxic cells?

A

natural killer cells, eosinophils

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11
Q

what is a phagocyte’s role?

A

phagocyte’s role is to seek, engulf and destroy pathogens via a process called phagocytosis

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12
Q

what are mast cells?

A

mast cells are white blood cells that are involved in the inflammatory response and release histamine which triggers the inflammatory response. They reside in the connective tissues throughout the body. When they detect injury in surrounding cells or are stimulated by antigens or allergens, they release histamine

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13
Q

what are macrophages?

A

large white blood cells that carry out phagocytosis and can act as an APC. They are found throughout the body and are attracted to the site of infection by cytokines. Macrophages are abundant in sites that are prone to infection and are one of the first cells to recognise pathogens that have breached the first line of defence

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14
Q

what is neutrophil?

A

short lives white blood cells in the bloodstream that are attracted to the site of infection by presence of cytokines. They carry out phagocytosis and release defensins that are toxic to bacteria and fungi. Neutrophils are the most common type of white blood cell and self destruct after consuming pathogens

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15
Q

what are dendritic cells?

A

white blood cells that have many folds and projections in it membrane to increase surface area which permits contact with a larger number of cells. They are found near the body’s surface and carry out phagocytosis and act as antigen presenting cells

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16
Q

what are natural killer cells?

A

white blood cells that are involved in the innate immune response and kill infected host cells through recognition of an absent or damaged MHC I marker. They release chemicals such as perforin and granzymes which which induce apoptosis and cell lysis. NK cells release cytokines to attract other specific adaptive immune cells to the area of infection

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17
Q

what are eosinophils?

A

white blood cells that target parasites and contain granules (cytotoxic chemicals) that target parasites

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18
Q

what are antigen presenting cells?

A

Antigen presenting cells are are phagocytes that perform phagocytosis and retain pathogenic fragments (such as their antigen fragments) and display them on their MHC II markers. Antigen presenting cells use their MHC II markers to communicate with other immune cells. They act as the bridge between the second and third line of defence and play a role in activating humoral and adaptive immune response.

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19
Q

what are phagocytes?

A

a group of white blood cells that are responsible for the destruction of pathogens and foreign material. They are able to undergo phagocytosis

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20
Q

why are phagocytes able to destroy invading pathogen?

A

this is because they contain highly toxic lysosomes which contain lysozymes that which can drastically lower the pH within the phagosome, assisting in degrading pathogenic contents and lysozymes also release content to digest phagosomes

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21
Q

what is phagocytosis?

A

a type of endocytosis in which solid substances (such as pathogens) enter a cell via vesical mediated transport

22
Q

what is a phagosome?

A

the vesicle that engulfs a pathogen during endocytosis

23
Q

what is the process of phagocytosis?

A
  1. receptors in the phagocyte recognise the microbe as non-self
  2. leads to the activation of the phagocyte
  3. Phagocyte engulfs the pathogen with the plasma membrane forming a vesicle called a phagosome around it
  4. lysozyme containing lysosomes fuses with the phagosome which breaks down the foreign material
  5. debris is released via exocytosis and antigens may be presented on MHC II markers if phagocyte is acting as an APC
24
Q

What are the receptors that a NK cell have and what do they bind to to initiate no response?

A

an NK cell has an inhibitory receptor and an activating receptor. The inhibitory receptor binds to a natural killer ligand and the activating receptor binds to the MHC I marker. When both receptors bind, the cell is recognised as healthy and no activation occurs

25
Q

How are NK cells attracted to infected cells

A

infected cells release interferons which attract NK cells

26
Q

When is a response initiated from an NK cell?

A

when an activating receptor doesn’t find MHC I marker so it is identified as unhealthy and non-self and a response from NK cell is initiated

27
Q

How does an NK cell destroy infected cells?

A

it released cytotoxins such as perforin and granzymes to cause apoptosis and cell lysis. The NK cell then releases cytokines to signal the infection to other immune cells.

28
Q

what is the molecule defence?

A

molecules that assist in defending against pathogens that have breached the first line of defence

29
Q

what are the different roles of complement proteins?

A

complement proteins are found in the blood and opsonise, cause lysis, and attract phagocytes to invading pathogens
when activated:
- cause lysis by inserting themselves into cell membrane of pathogens creating a pore. Water and ions enter the cell and cell swells and lyses
- attract phagocytes to site of infection
- attach to invading organisms and act as flags making pathogen more readily identifiable
- contribute to inflammation by increasing local permeability of capillaries

30
Q

what are cytokines?

A

signalling molecules of the immune system, released by immune cells and acts on other specific immune cells to activate further adaptive immune responses. Examples include interferons and interleukines

31
Q

what are interferons?

A

a type of cytokine released by virally infected cells that increase the viral resistance of neighbouring uninfected cells

32
Q

what can interferons do to prevent further viral infection?

A

-activates the virally infected cell to produce enzymes that break down viral RNA and proteins that block translation
- signals to neighbouring uninfected cells to reduce protein synthesis and also produce enzymes that break down viral DNA and proteins that block translation
- signals to neighbouring infected cells to undergo apoptosis
- attracts Natural killer cells to release perforins to kill virally infected cells
- warns nearby cells, making them more resistant, keeping virus outside of cells so that it is more susceptible to phagocytosis

33
Q

what is histamine?

A

a signalling molecule released by mast cells which initiates the inflammatory response

34
Q

what are chemokines?

A

act as chemical attractants that are important in attracting leukocytes to site of infection and inflammation

35
Q

what is apoptosis?

A

death and disintegration of a cell through a series of controlled steps

36
Q

what is cell lysis?

A

when holes are punched in the cell causing it to rupture

37
Q

what are the two ways in which interferons are released and what do they mean?

A

autocrine manner: the autocrine signal acts on the cell itself and triggers the production of proteins that will inhibit viral proteins from being synthesised within it

paracrine manner: acts on nearby cells allowing uninfected cells to prepare for the production of inhibitory proteins in case they get infected.

38
Q

what is the inflammatory response?

A

a physiological response to a pathogen breaching first line of defence and is characterised by redness, heat, pain and swelling

39
Q

what are the symptoms of the inflammatory response and why are they caused?

A

symptoms: pain, swelling, redness and heat
heat and redness: capillary widening increases blood flow to the site of infection resulting in increased heat and redness
pain: extra pressure due to excess fluid applies pressure to nerve endings, causing pain
swelling: increased permeability causes leaky blood vessels and as a result, there can be fluid build up in tissue, causing swelling

40
Q

what is vasodilation?

A

widening of blood vessels to increase blood flow

41
Q

what role does cytokines play in the inflammatory response?

A

damaged cells from the breached sin release cytokines to attract second line of defence cells (neutrophils and macrophages) and molecules to the site of infection

42
Q

what do the platelets do in the inflammatory response?

A

they travel to the wound and stop active bleeding. They release clotting factors to prevent further bleeding at breech site.
- they block blood vessels which can prevent the pathogen from entering the blood stream and spreading infection to other parts of the body
- also assist in re-establishing the physical barrier to aid first line of defence

43
Q

what do mast cells do in the inflammatory response?

A
  • release histamine that travel to nearby blood vessels to initiate vasodilation of local blood vessels
44
Q

function of vasodilation

A
  • increases blood flow and permeability of blood vessels
  • enables more second line molecules and cells to come to the site of infection and leave the blood vessels
45
Q

what do the complement proteins do in the inflammatory response?

A

complement proteins are activated and attach to the pathogen to cause cell lysis, attract phagocytes and aid in immobilising the pathogen

46
Q

what do the macrophages do in the inflammatory response?

A
  • release cytokines
  • are attracted to the site of infection by cytokines
  • engulfs pathogen via phagocytosis and retains antigens
  • can act as an APC
47
Q

function of neutrophil in the inflammatory response

A
  • leave the blood vessels and are attracted to the site of infection by presence of cytokines
  • engulfs pathogen via phagocytosis
  • release defensins that target and disrupt bacterial and fungal membranes
  • release further cytokines to attract more immune cells
48
Q

what is fever?

A

rise in body temperature caused by infection

49
Q

why is fever beneficial in the inflammatory response?

A

cytokines in the inflammatory response can also cause fever because the rise in body temperature helps body fight the infection. Bacteria and viruses prefer lower body temperatures to efficiently replicate while immune cells perform slightly better at higher temperatures.

50
Q

what is the process of the inflammatory response?

A
  1. Damage to skin where first line of defence is breached, allowing pathogens to enter the body. Damaged skin cells release cytokines and activate blood clotting factors
  2. Mast cells are activated to release histamine which causes vasodilation of blood vessels making it more permeable through formation of gaps and increasing blood flow
  3. complement proteins are activated, leave the blood cells and cause lysis of pathogens , coating them for easier identification for [phagocytes
  4. Neutrophils attracted to the infection, leave the blood vessels, release defensins and assist macrophages in performing phagocytosis and secreting cytokines
  5. Inflammatory response continues until pathogen is eliminated
51
Q

How does the inflammatory response terminate

A

Once pathogen is eliminated, phagocytes die and are removed by carefully controlled apoptosis
- when no longer required, the inflammatory response is switched off
- The response continues until the site has been cleared of pathogen and debris

52
Q

what is pus composed of?

A

Pus is a fluid containing large amounts of dead immune cells such as neutrophils and also pathogens debris and fragments

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