Functioning of acquired and innate immune system

Question 1

What are pathogen associated molecular patterns (PAMPs)?

Answer 1

• Receptors that can recognise differences
• Viruses have a glycoprotein envelope
• Bacteria have peptidoglycan, unlike other organisms
• Immune system able to detect these differences

Question 2

What are pattern recognition receptors?

Answer 2

• E.g. toll-like receptors (TLR)
• Germ-line encoded receptors
• Expressed on surface of innate cells
• Broad binding profile, able to recognise many different pathogens
• TLR have similar structures
• Right place right time, high specificity
• PRR bind to PAMPs leads to activation of macrophages and pathogen uptake
• Phagocytosis
• Many receptors that will recognise differences

Question 3

What are the only cells that can activate T cells without antigens?

Answer 3

Dendritic cells

Question 4

What do dendritic cells do upon the presence of a foreign antigen?

Answer 4

• Enter lymph nodes

- Present peptide antigen to T cells

Question 5

How is the peptide antigen presented by dendritic cells?

Answer 5

• Peptide complex with MHC molecules
• Antigen detected by T cell
• MHC Class 1- CD8 receptor- cytotoxic T cell
• MHC Class 2- CD4 receptor= helper T cell

Question 6

Describe the endogenous pathway of T cell activation

Answer 6

• MHC (HLA) Class 1

- Peptides come from intracellular proteins- fragmented and loaded onto class 1 to activate CD8 receptors

Question 7

Describe the exogenous pathway of T cell activation

Answer 7

• MHC (HLA) Class 2

- Antigen taken from outside- vesicles loaded onto MHC Class 2 to activate CD4 receptors

Question 8

How are B cells activates?

Answer 8

• Detect whole antigen using B cell receptor
• Causes activation, proliferation and differentiation
• Can receive help from CD4 T cells

Question 9

What are the 5 types of heavy chain that give rise to different immunoglobulin?

Answer 9

• IgM
• IgG
• IgA
• IgF
• IgD

Question 10

Describe the specificity of the adaptive response

Answer 10

• Single antigen receptor
• Able to generate 1x10 (^14) different specificities
• Fine tuning during course of response improves
• Achieved with surface complementary to antigen
• B cell receptor + protein
• T cell receptor + MHC Class 1

Question 11

How is diversity achieved?

Answer 11

• Gene arrangement to create BcR
• 3 CDR regions that interact- V, D and J
• Heavy chain- 10^14, V, D and J
• Light chain- 1x10^2 and 1x10^2- V and J regions only create binding site
• Splicing- imprecise joining creates 1x10^2
• Random addition of nucleotides- 1x10^2
  -Light- 10^6, Heavy- 10^8
  = 1x10^14

Question 12

What is cytotoxic T cell’s method of killing?

Answer 12

• Recognised by foreign antigen
• Cytoplasm of T cell rearranged to aim toxic proteins (performs and granzymes)
• Fusion of T cell membrane with microbe membrane- perforin action
• Cells can no longer regulate processes and die
• Granzymes enter cells

Question 13

Describe perforin action

Answer 13

Puncture the membrane via pores, contents leave the cell

Question 14

Describe granzyme action

Answer 14

Enter cells and activate apoptosis

Question 15

Describe antibodies

Answer 15

• Five classes
• IgG- highly specific (activates compliment cascade, results in membrane attack)
• Peptides presented to immune cells
• Antibodies able to bind to toxins
• Aggregation of bacteria
  (immune complex for phagocytes, detects proteins leads to opsonisation)

Question 16

What is opsonisation?

Answer 16

• Microbes are chemically modified to have a stronger attraction to cell surface receptors of phagocytes