WEEK 10: 10.2 The Innate Immune System

Question 1

What are the characteristics of innate immunity

Answer 1

Non-specific immunity
Frontline defense
Self/Non-self recognition: ability to recognise common patterns in pathogens
No memory
Not weak
Link into the adaptive immunity

Question 2

What are mechanical barriers to infection

Answer 2

Skin and GI tract: longitudinal flow of air/liquid
Resp tract: movement of mucus by cilia
Eyes: tears
Skin, GI, resp, eyes: epithelia joined by tight junctions

Question 3

What are physiological and chemical barriers to infection

Answer 3

Skin: fatty acids (lower pH)
GI tract: Low pH (HCl) , enzymes (digest protein & bacteria)
Eyes: lysozyme (enzymes clears cell wall)
Skin, GI, resp: antibacterial peptides (punch holes on bacterial surface)

Question 4

What are microbiological barriers to infection?

Answer 4

Skin, GI tract, resp tract: normal flora that compete

Question 5

what are characteristics of the anatomical barrier; epidermis

Answer 5

dead outer layer
continuous epithelium
impermeable
shed 10-15 so bacteria can’t stay for long
competing normal flora

Question 6

what are characteristics of the anatomical barrier; dermis

Answer 6

vascularised
connective tissue
glands including the sebaceous gland, which lowers pH
Sebum (lactic and fatty acids)

Question 7

Where are the anatomical barriers of mucous membranes found?

Answer 7

in conjunctivae, respiratory, alimentary and urogenital tracts

Question 8

what are mucous membranes composed of?

Answer 8

mucus, outer epithelia & connective tissue layers

Question 9

What is mucus produced by?

Answer 9

goblet cells

Question 10

What does mucus have high viscisoty?

Answer 10

It is a biological gel, this allows it to trap microbes

Question 11

What is mucus made of?

Answer 11

mucin (glycoproteins), anti-microbial proteins, inorganic salts

Question 12

Where is mucus found?

Answer 12

saliva and tears

Question 13

What is cilia

Answer 13

hairy-like structures on columnar cells in the epithelia

Question 14

What do commensal microbes do?

Answer 14

they digest dietary fibres to produce metabolites, vitamins and short chain fatty acids to maintain a healthy colon, as well as compete with pathogenic microbes for nutrients and space

Question 15

What antimicrobial substances do commensal microbes release?

Answer 15

lactic acid - more acidic env due to influx of H+ ions
bacteriocins - antimicrobial peptides that destroy neighboring bacteria

Question 16

Under what circumstances can commensal microbes cause disease?

Answer 16

opportunistic pathogens - when an immunocompromised individual has a weaker immune system commensals can take take over

Question 17

What are examples of soluble barriers in innate immunity?

Answer 17

antimicrobial peptides
complement
opsonins
cytokines

Question 18

What is the general mode of action of AMPs

Answer 18

cationic proteins that disrupt membrane integrity

Question 19

What is an example of an AMP

Answer 19

defensin

Question 20

what are AMPs produced by?

Answer 20

epithelium of skin (keratinocytes), mucosa, neutrophils and macrophages

Question 21

Describe the 3 ways of complement activation

Answer 21

classical pathway - C recognises antibody and activates antigen complex
alternative pathway- C binding generally onto microbe surface
Lectin pathway- C binds onto sugar residues on bacteria surface

Question 22

What does complement activation lead to?

Answer 22

Cascade activation of complement proteins

Question 23

What are the 3 outcomes following complement activation?

Answer 23

1. Opsonisation: coat surface with C3b proteins to promote phagocytosis
2. Initiation of inflammatory response: release anaphylatoxins which bind to immune cells to trigger inflammatory response, chemoattractant to phagocytes
3. Punches holes in cell membrane: formation of membrane attack complex on surface of target cells

Question 24

What are different types of cellular barriers in innate immunity? briefly describe them

Answer 24

macrophages (lives in tissue, comes from monocytes, professional phagocyte)
neutrophils (first immune cell against bacteria, professional phagocyte)
natural killer cells (kills tumor cells, cells infected by virus, cells infected by intracellular bacteria)
basophils/mast cells (inflammatory response)

Question 25

How do natural killer cells kill?

Answer 25

via apoptosis

Question 26

How do professional phagocytes kill?

Answer 26

Via phagocytosis of extracellular bacteria

Question 27

How does endocytosis occur, and what is it?

Answer 27

It is the ingestion of macromolecules, internalisation via small vesicles formed by membrane invagination

Question 28

what are the 2 major mechanisms of endocytosis?

Answer 28

Pinocytosis - nonspecific receptor mediated endocytosis- specific

Question 29

What is phagocytosis and how does it occur in 3 steps

Answer 29

it is the ingestion of particles 1. plasma membrane expands, forms pseudopods 2. pseudopods retract, seal itself into phagosome 3. phagosome fuses with lysosome

Question 30

What are opsonins, and what is their function?

Answer 30

they are soluble proteins they recognise unique structures like carbs, then tag these microbes and bind to opsonin receptor on phagocytes to make the microbes more palatable

Question 31

what 2 forms of recognition triggers phagocytosis?

Answer 31

recognition of microbes through pattern recognition receptors recognition of microbes indirectly through opsonin receptors

Question 32

Describe in 5 steps, how NKs trigger apoptosis

Answer 32

1. NK recognises tumor/viral infected cell 2. contents from granules in the NK undergo degranulation, signaling the self-cell to undergo apoptosis 3. cell self-destructs, DNA and organelles break down and cell blebs to form apoptotic bodies 4. blebs isolate cytoplasmic contents 5. apoptotic bodies and phagocytosed by professional phagocytes