L7 Innate Immunity

Question 1

What is innate immunity?

Answer 1

The recognition of antigens by non-specific Pattern Recognition Receptors

Receptors are germline encoded

Question 2

What are the functions of innate immunity? [3]

Answer 2

Prevent infection
Promote acute inflammation
Respond rapidly

Question 3

Innate mechanical barriers to infection

Answer 3

Skin: Epithelial cells joined by tight junctions. Longitudinal flow of air or fluid

Gut: Epithelial cells joined by tight junctions. Longitudinal flow of air or fluid

Lungs: Epithelial cells joined by tight junctions. Movement of mucus by cilia

Eyes/nose: Epithelial cells joined by tight junctions.

Question 4

Innate chemical barriers to infection

Answer 4

Skin: FA and antibacterial peptides

Gut: Low pH and enzymes (pepsin) + antibacterial peptides

Eyes/nose: Salivary enzymes (lysozymes)

Question 5

Innate microbiological barriers to infection

Answer 5

Skin: Normal flora

Gut: Normal flora

Question 6

How do the antigen receptors of innate immunity work?

Answer 6

Antigen receptors of innate immunity detect antigens non-specifically using receptors for ‘pathogen-associated molecular patterns’ (PAMPS)
PAMPS are patterns of molecules that occur in lower organisms, but do not occur in humans
These receptors are called pattern recognition receptors (PRRs)
This is an effective mechanism for distinguishing self from non-self

Question 7

What are toll-like receptors?

Answer 7

Toll-like receptors (TLRs) are an example of a pattern recognition receptor. Drosophila with TLR mutations were susceptible to fungal infection

Question 8

What is MBL?

Answer 8

Mannose binding ligand

Example of PRR

Binds with high affinity to mannose and fucose residues with correct spacing

Question 9

What do natural killer cells do?

Answer 9

NK cell recognises antibody-coated bacteria by Fc receptor; the target organism is then killed by non-phagocytic means

Process known as antibody-dependent cellular cytotoxicity (ADCC)

Question 10

What are eosinophils?

Answer 10

Believed to be important in defence against parasites
Local infiltration at sites of infection
Numbers in blood increase during parasite infection

Granules contain toxic enzymes
Can perform antibody-dependent cellular cytotoxicity

Also found at sites of allergic inflammation

Question 11

Cytokines and systemic inflammation - liver

Answer 11

Acute-phase proteins (C-reactive MBL)

Activation of complement opsonisation

Question 12

Cytokines and systemic inflammation - bone marrow endothelium

Answer 12

Neutrophil mobilisation

Phagocytosis

Question 13

Cytokines and systemic inflammation - hypothalamus

Answer 13

Increased body temperature

Decreased viral and bacterial replication.
Increased antigen processing.
Increased specific immune response.

Question 14

Cytokines and systemic inflammation - fat, muscle

Answer 14

Protein and energy mobilisation to allow increased body temperature

Decreased viral and bacterial replication.
Increased antigen processing.
Increased specific immune response.

Question 15

What is complement and what does it do?

Answer 15

Complement is a series of enzymes that are produced in the liver and circulate in the bloodstream
The enzymes circulate in inactive form
When the first enzyme is activated, it goes on to activate the next in the sequence, which then activates the next and so on
This is called a ‘triggered enzyme cascade’

Question 16

What is opsonisation by complement?

Answer 16

Complement plays a role in opsonisation, along with antibody

Activated complement component C3b sticks to pathogens

Binds to phagocyte C3b receptors

Question 17

What is alpha interferon and what does it do?

Answer 17

Soluble innate mediator

Production activated by viral infection

Work locally on surrounding cells

Question 18

What are the antiviral effects of interferons?

Answer 18

Stop cells dividing

Stop cells synthesising new proteins

Stimulate production of anti-viral proteins by host cell

Question 19

What is cell lysis by the terminal pathway?

Answer 19

Terminal pathway components assemble a ‘pore’ which inserts into pathogen membranes

Question 20

What are the interactions between innate and adaptive immunity?

Answer 20

Inflammation attracts T and B cells to local lymph nodes for activation

Innate immunity a key effector mechanism for antibodies

• Opsonisation/ phagocytosis
• Antibody-antigen complex/ complement
• Mast cells

Innate immunity is also directly required to activate T cells;