Introduction to immune response

Question 1

What is the innate immune response?

Answer 1

Innate immune response is the immune response we are born with.

It produces a non-specific response

Question 2

What are some barriers that repel pathogens in the innate immune system?

Answer 2

• Chemical barriers- lysozyme (tears), low stomach pH creating acidic environment
• Physical barriers- Epithelium (skin/gut), cilia lining airways

Question 3

How does lysozyme acts as a barrier to infection?

Answer 3

• It acts as a mechanism to kill bacteria by hydrolysing their peptidoglycan cell walls , so it’s especially effective against gram-positive bacteria

Question 4

How does low stomach pH act as a barrier to infection?

Answer 4

The low pH kills most microorganisms that are ingested

Question 5

What are the key features of the innate immune system?

Answer 5

• Non-specific cells that do not distinguish invaders
• Response occurs within minutes-hours
• No memory cells
• Always respond to pathogen in the same manner

Question 6

Define phagocytosis

Answer 6

The ingestion of bacteria or other pathogens by phagocytes

Question 7

What cells are phagocytes?

Answer 7

Monocytes
Macrophages
Neutrophils
Basophils
Eosinophils
Mast cells
Dendritic cells

Question 8

What is the function of monocytes?

Answer 8

Monocytes reside in blood and tissues to find and destroy pathogens, and eliminate infected cells

Question 9

What is the function of macrophages?

Answer 9

Recognise pathogen and activate innate immune system

Destroy infectious organisms that enters the body, clear cellular debris and wound healing

Question 10

What is the function of neutrophils?

Answer 10

Cells that travel to site of infection, where they destroy microorganisms by ingesting them and releasing enzymes that kill them (phagocytosis)

Question 11

What is the function of basophils?

Answer 11

• Immune surveillance
• Play key role in response to allergies - release histamine which enlarges blood blood vessels to improve blood flow and heal affected area
• Histamine also allows other cells to quickly target and respond to allergen

Question 12

What is the function of eosinophils?

Answer 12

• Active pathogenic role in inflammation associated with allergic disorders.

Question 13

What is the function of mast cells?

Answer 13

Contain chemicals such as histamines, heparin, cytokines that play a role in immune restore to certain bacteria and parasites, and other types of immune response

Question 14

What is the function of dendritic cells?

Answer 14

• They capture, process and present antigens from pathogen to immune cells (T and B cells) and mediate their polarisation into effector cells, therefore these activate the specific (adaptive) immune system

Question 15

What are the 4 stages of phagocytosis?

Answer 15

Stage 1 - Recognition of the target particle (opsonisation) and chemotaxis
Stage 2 - Signalling to activate immune system
Stage 3- Phagosome formation
Stage 4- Phagolysosome maturation

Question 16

Explain the first stage of phagocytosis, recognition of the target particle and chemotaxis

Answer 16

• Pathogens release inflammatory mediators (inflammatory cytokines, complement proteins etc), called Pathogen Associated molecular patterns (PAMPs)
• Resting phagocytes are activated by these, resulting in circulating phagocytes producing surface glycoprotein receptors, increasing their ability to adhere to inner surface of capillary walls, and move to the site of infection (this is chemotaxis).
• Receptors on the plasma membrane of phagocytes can release opsonin, which coats cells or pathogens so phagocytes become attracted to them (opsonisation)

Question 17

Explain the second stage of phagocytosis, signalling to activate immune system

Answer 17

• Phagocytic receptors initiate signalling cascades that remodel lipids in the cell membrane and regulate the actin cytoskeleton to extend the cell membrane around the pathogen
• Phagocytic receptors engage in a sequential order and cooperate to complete the formation of the phagosome

Question 18

Explain the third stage of phagocytosis, phagosome formation

Answer 18

• Phagocytic receptors interact with ligands on the surface of target pathogens
• Receptors aggregate to initiate signalling pathways that regulate the actin cytoskeleton, so that the phagocyte can produce membrane protrusions for involving the particle.
• Finally, the particle is enclosed in a new vesicle, called the phagosome

Question 19

Explain the fourth stage of phagocytosis, phagolysosome maturation

Answer 19

• The phagosome fuses with lysosomes
• The membrane changes its membrane composition and contents to turn into a phagolysosome, a vesicle that can release digestive lysosomes to destroy the pathogen. This transformation is phagosome maturation.
• Phagosome maturation consists of successive fusion and fission interactions between the phagosome and endosomes, late endoscopes and finally lysosomes to become a phagolysosome. This is because the phagosome fuses with lysosomes when it becomes a late stage phagosome through interaction with endoscopes.
• At the end, the phagolysosome has a different membrane composition, which allows it to contain a very acidic and degradative environment, which allows it to kill and digest pathogens
• Continues to swallow pathogens before oxidative burst-> Produces highly reactive oxygen e.g. H2O2; destroys proteins, nucleic acids, killing pathogens and the phagocyte

Question 20

How does phagocytosis remove dead cells?

Answer 20

• Dying cells secrete a ‘find me’ signal, and they expose this signal on their surface.
• Phagocytes ingest the dead cells, direct them to lysosomes, and degrade their cellular components into basic biochemical building blocks: amino acids, nucleotides, fatty acids, and monosaccharides.
• These molecules will be released from the lysosomes and reused to make new macromolecules

Question 21

What are the cell types in the adaptive immune response?

Answer 21

• T helper cells
• Cytotoxic T cells
• B cells
• Plasma cells

Question 22

What are the functions and properties of T helper cells?

Answer 22

• Involved in cell-mediated response
• Recognises antigens presented by MHC class II molecules
• Expresses CD4, CD3, TCR, CD28
• Major source of IL-2
• Mediates acute and chronic organ rejection

Question 23

What are the functions and properties of Cytotoxic T cells?

Answer 23

• Involved in cell-mediated response
• Recognises antigens presented by MHC class I molecules
• Induce apoptosis in virally infection and tumour cells
• Expresses CD8
• Also expresses CD3, TCR
• Mediates acute and chronic organ rejection

Question 24

What are the functions and properties of B cells?

Answer 24

• Major cell of humoral immune response
• Acts as an antigen presenting cell
• Mediates hyperacute organ rejection

Question 25

What are the functions and properties of plasma cells?

Answer 25

• Differentiated from B cells
• Produces large amounts of antibody specific to a particular antigen

Question 26

What is the function of T lymphocytes?

Answer 26

• T lymphocytes increase apoptosis to destroy cells that have been hijacked by viruses and pathogens

Question 27

What is the function of B lymphocytes?

Answer 27

• B cells release antibodies used to attack invading pathogens