Innate Immunity I

Question 1

Describe neutrophils

Answer 1

• Most abundant phagocytes/first line of defence
• Degranulation, phagocytosis and antigen presentation occur

Question 2

Describe phagocytosis.

Answer 2

• Attach to microorganisms by cell surface receptors
• Pseudopods extend and fuse - form phagosome - fuse with lysosome - forms phagolysosome
• Lysosomal enzymes break down microbe
• Residual waste exocytosed

Question 3

Describe eosinophils.

Answer 3

• Produced in response to parasitic infections
• Involved in IgE mediated allergic disorders
• Prevent spread of inflammation by collecting in response to chemotactic factors from mast cells

Question 4

Describe basophils.

Answer 4

• Release heparin - prevent coagulation
• Bind to IgE antibodies - role in allergic reactions (type 1 hypersensitivity)

Question 5

Define mast cells.

Answer 5

• Release histamines and produces cytokines
• Involved in tissue repair and wound healing
• Hypersensitivity reactions
• Histamines cause dilation of small blood vessels, increase in vascular permeability

Question 6

Describe monocytes

Answer 6

• Produced in bone marrow and travel to tissue - mature and become macrophages
• Roles in phagocytosis, antigen presentation and cytokine production
• Survive following phagocytosis for months

Question 7

Describe macrophages.

Answer 7

• Effector cells of innate immune system
• Develop from monocytes
• Perform antigen presentation/activate memory cells
• Can be fixed/free

Question 8

Describe natural killer cells.

Answer 8

• Role in adaptive/innate immunity
• Non-phagocytic
• Induce apoptosis, attack cells lacking cell surface receptors

Question 9

What is the main difference between apoptosis and necrosis?

Answer 9

APOPTOSIS - programmed cell death
NECROSIS - accidental cell death

Question 10

Describe antigen-presenting cells.

Answer 10

• Innate immune cell - activates adaptive immunity
• Detects phagocytosis and digests pathogen to form antigen fragments
• Presented using MHCs
• EXAMPLES: Dendritic cells/B cells/macrophages

Question 11

Define dendritic cells

Answer 11

• Main APC - activate T helper and memory cells
• Form in bone marrow, circulate in bloodstream, activated by pathogens and mature at target tissues
• MIgrate to lymph nodes where antigen-specific immune response develops
• EXAMPLES: Langerhans cells in skin

Question 11

What is the difference between MHC Class I and II? PART 1

Answer 11

• CLASS I - displayed by all nucleated cells, recognised by naive CD8 cells/cytotoxic T cells, foreign antigens are endogenous

Question 12

What is the difference between MHC Class I and II? PART 2

Answer 12

• CLASS II - displayed by APCs, recognised by T helper cells/naive CD4 cells/foreign antigens are exogenous

Question 13

Describe immature dendritic cells

Answer 13

• Phagocytose pathogens, degrade proteins into small pieces
• Once antigen encountered, activated into mature cells and migrates to lymph nodes
• Upon maturation, present antigen fragments on cell surface using MHC Class II

Question 14

Outline how immature dendritic cells mature. PART 1

Answer 14

• Senses pathogen/inflammatory signals
• Phagocytose microbe
• Upregulate expression of CD80/CD86 receptors involved in T cell activation

Question 15

Outline how immature dendritic cells mature. PART 2

Answer 15

• Upregulate CCR7 - chemokine receptor - allows mature dendritic cell to travel through bloodstream to lymph nodes in response to chemokines
• Decreased phagocytic capability
• Greater expression of MHC II - release cytokines/chemokines

Question 16

How can dendritic cells be involved in disease?

Answer 16

HIV
- Bind to dendritic cells via receptors
- Travel to lymph nodes
- Transferred to CD4+ T helper cells

Question 17

What are Toll-like receptors?

Answer 17

• Dendritic cells identify pathogens by recgonising PAMPs using pathogen-recognition receptors (PRRs)
• EXAMPLE OF PRRs: Toll-like receptors - link PAMPs to transcription factor activation

Question 18

Give some examples of inflammatory mediators.

Answer 18

• Cytokines
• Chemokines
• Lipid mediators e.g prostaglandins

Question 19

Describe cytokines.

Answer 19

• Proteins secreted by immune cells e.g neutrophils, macrophages, NK cells
• Affects behaviour of other cells
• Involved in innate/acquired immunity

Question 20

Describe interferons.

Answer 20

• Cytokines produced in response to viral infection
• Cause anti viral state in target cells
• Shuts down protein synthesis machinery, preventing viral replication

Question 21

Outline the role of interleukins

Answer 21

• Inflammation
• Immune cell proliferation and activation
• Increase antibody production

Question 22

Outline the steps in phagocyte mobilisation. PART 1

Answer 22

• LEUKOCYTOSIS - neutrophil release in response to inducing factors
• MARGINATION - endothelial cells of capillaries in inflamed area project CAM - attach to neutrophils - roll across vessel wall

Question 23

Outline the steps in phagocyte mobilisation. PART 2

Answer 23

• DIAPEDESIS - movement of neutrophils into interstitial spaces by flattening and squeezing between endothelial cells
• CHEMOTAXIS of neutrophils towards area of injury
• Monocytes arrive - form macrophages