7C: Second Line of Defence

Question 1

Second Line of Defence

Answer 1

a component of the immune system characterised by the non-specific and immediate response to injury and pathogens by a variety of cells and molecules

- The backup plan for when pathogens slip past the first line of defence
- Composed of cellular and noncellular components
- All the cells involved are leukocytes

Question 2

Leukocytes

Answer 2

a group of blood cells responsible for protecting the body against pathogens and foreign material

- Also known as white blood cells

Question 3

Cytokines

Answer 3

a signaling molecule released by cells which aid in communication between immune cells and helps protect against pathogens

- Typically found in the immune system
- Guides the immune cells to the site of infection or injury

Question 4

Phagocytes

Answer 4

a group of leukocytes responsible for the endocytosis and destruction of pathogens, foreign material and cell debris

- The process is known as Phagocytosis
    - Communicate within the immune system by releasing a number of substances such as cytokines

Question 5

Process of Phagocytosis

Answer 5

• Pathogen, Foreign material or dead material is consumed through endocytosis.
  
  • Lysosomes contain lysozymes destroy the Pathogen, foreign or dead material by fusing with the vesicle.
  • Pathogen, foreign or dead material is broken into smaller fragments.

Question 6

Types of Phagocytes: Neutrophils

Answer 6

the most common type of leukocyte which engages in phagocytosis of pathogens as well as the release of cytokines

Question 7

Types of Phagocytes: Macrophages

Answer 7

a type of leukocyte found throughout the body that engages in phagocytosis and antigen presentation

Question 8

Types of Phagocytes: Dendritic Cells

Answer 8

a type of leukocyte that engages in phagocytosis and antigen presentation

• Stimulate an immune response

Question 9

Antigen - Presenting Cell

Answer 9

a subgroup of phagocytes that display antigens from consumed pathogens on their surface and interact with the adaptive immune system

- Macrophages and dendritic cells are also antigen presenting cells

Question 10

Natural Killer Cells(NKC)

Answer 10

a large granulated leukocyte responsible for the recognition and destruction of damaged and or infected host cells

- Achieved through the presence of receptors

Question 11

Types of NKC Receptors: Killer Inhibitory Receptor

Answer 11

• Killer Inhibitory Receptor: examines the surface of cells for MHC I markers
• If the killer inhibitory receptor detects a sufficient number of MHC I markers, then it overrides the killer activation signal, preventing cell death

Question 12

Types of NKC Receptors: Killer Activation Receptor

Answer 12

• Killer Activation Receptor: binds to certain molecules which appear on cells undergoing cellular stress
• If the killer activation receptor is activated and the killer inhibitor receptor is unable to bind to sufficient MHC I markers, cell death occurs

Question 13

Degranulation

Answer 13

the release of contents from a cell

- E.g. Mast cells releasing histamine 
- E.g. Eosinophils releasing their chemical mediator

Question 14

Mast Cells

Answer 14

a type of leukocyte responsible for releasing histamine during allergic and inflammatory responses

- Reside in connective tissue
- When they detect an injury, they activate and degranulate(release contents), releasing histamine

Question 15

Histamine

Answer 15

a molecule released by mast cells which plays a key role in the inflammatory response

- Causes vasodilation, increases permeability of blood vessels and act as a chemoattracter to phagocytes

Question 16

Eosinophils

Answer 16

a large granular leukocyte responsible for the release of toxic chemical mediators

- Contains chemicals such as DNases, RNases and proteases which all help destroy invading pathogens
- Typically target pathogens too large to be phagocytosed by degranulating on contact with them and releasing the chemical mediator

Question 17

Interferons

Answer 17

a type of cytokine released by virally infected cells that increases the viral resistance of neighboring uninfected cells by causing them to undergo a number of changes

- Helps prevent the virus from spreading between cells

Question 18

Complement Proteins

Answer 18

a number of different types of proteins found in the blood that in the presence of certain pathogens, begin reacting together causing three major outcomes to assist phagocytes eliminating pathogens

- Reaction is known as the complement cascade - Outcomes are opsonization, chemotaxis, lysis

Question 19

Outcomes of the Complement Cascade

Answer 19

• Opsonisation: complement proteins stick to the outside surface of the pathogen and make it easier for the immune system, such as phagocytes, to recognise them as foreign
  
  • Chemotaxis: complement proteins gather near a pathogen, attracting phagocytes to it, making it more likely to be destroyed
  • Lysis: complement proteins join together on the surface of the pathogen forming a Membrane Attack Complex which creates pores in the membrane, destroying the pathogen with a sudden influx of fluid entering the pathogen causing it to burst

Question 20

Fever Immune Response

Answer 20

• Involves the temporary increase in body temperature
  • This is an innate response to potential infection as many pathogens cannot survive at the elevated temperatures caused by fevers
  • Also though to help by activating certain proteins in the body that bolster the strength of the body’s defences
  • Prolonged fevers however can be detrimental to the body due to cells not functioning at their optimal temperature

Question 21

Inflammatory Response

Answer 21

a response designed to eliminate the effects of an injury, defend against potential pathogens, clear out cells that may be damaged or destroyed and initiate repair

- The response will continue until the site has been cleared of the pathogen and debris and the site of injury has been healed and will eventually return to normal

Question 22

Steps in the Inflammatory Response

Answer 22

1. Initiation:
   
   • In response to an injury, Cytokines are released by immune cells
   • Mast cells degranulate releasing histamine
   2. Vasodilation:
      - Histamine released travels to nearby blood vessels and binds to specific receptors
   • causing vasodilation which increases blood flow to the injury site causing swelling, redness and warmth
   • Gaps in blood vessels also form, increasing its permeability to cells of the immune system
   3. Migration:
      - Vasodilation and increased permeability of blood vessels allow for:
      ○ Phagocytes to enter the site of injury and phagocytose pathogens

       ○ Complement proteins to be attracted to pathogens and make it easier for phagocytes to destroy them