Innate immunity: Basics and Phagocytosis

Question 1

How do pathogens enter

Answer 1

Mucosal and epithelial - skin - surfaces
External barrier

Question 2

How can pathogen cause infection

Answer 2

Pathogen must enter the body - breach one of these barriers
Diff routes of entry
- ex = airborne microorganisms enter through lining of respiratory tract

Question 3

Why is human skin resistant to colonization by E. coli despite exposure to it

Answer 3

Physical barriers = also chemical barrier
Skin has barrier against it

Question 4

Describe epithelial surfaces

Answer 4

Provide first barrier against infection = skin, gut lining epithelium, respiratory epithelium, mucosal membranes
Epithelial cells have prrs that bind pamps

Question 5

What provides innate immunity

Answer 5

Saliva
Hair
Mucus
Tears

Question 6

What do epithelial layers produce

Answer 6

Protective substances = acidic ph, antimicrobial peptides (defensins)

Question 7

Name cellular elements of innate immunity

Answer 7

Neutrophils (main) and other granulocytes
Monocytes and macrophages
Dendritic cells
Nk cells and other innate lymphoid cells

Question 8

Describe monocytes and macrophages

Answer 8

Macrophages = mostly tissue resident
Tissue specific variants = kupffer cells, microglia (macrophages of cns) , intraglomerular mesangial cells

Question 9

Name types of dendritic cells = 3

Answer 9

Immature

Mature =
conventional
Plasmacytoid

Question 10

Name some key molecules innate immunity

Answer 10

Antimicrobial enzymes
Antimicrobial peptide s
Complement

Question 11

Give ex of anti microbial enzyme

Answer 11

Lysozyme= digest peptidoglycan (cell wall gram pos bacteria)

Question 12

Give ex of anti microbial peptides

Answer 12

Defensins —> disrupt cell membrane (creates pore)

Question 13

Describe stages of infection and response to it

Answer 13

Pathogens adhere to epithelium
Immune cells activated = local infection, penetration of epithelium
Local infection of tissues
Adaptive immunity

Question 14

What is definition phagocytosis

Answer 14

Engulfment and internalization of pathogens or their comments upon binding to receptors on cell surface of phagocytes = have to be prompted

Question 15

Name phagocytes that mediate phagocytosis

Answer 15

Macrophages
Granulocytes:neutrophils
Dendritic cells

Question 16

What can phagocytosis lead to

Answer 16

Removal and killing of pathogens
Clearing debris= prrs recognize damps (released when cells near during, damage associated molecular patterns)
Generation of peptides for presentation to t cells

Question 17

Describe macrophage as phagocyte

Answer 17

Also dendritic cells can do phagocytosis and process antigen
Macrophages = presenting peptide antigen to T cell on mhc

Question 18

Describe receptors involved in phagocytosis

Answer 18

Many are prrs
Not all prrs induce phagocytosis - but many do

Question 19

Describe indirect phagocytosis

Answer 19

Phagocyte recognition of soluble proteins that are bound to microbial surfaces (opsonins, bind to surface of microbe ) = aka soluble pattern recognition proteins —> enhance phagocytosis (opsonization)
Ex = antibodies and complement proteins, phagocytic cells have receptors for opsonins

Question 20

Describe phagocytosis - initial

Answer 20

Initiated when receptors interact with ligand/pathogen
Bacterium binds to prrs (pamp binds)
Prompts membrane protrusions that extend = pseudopodia —> leads to engulfment bacteria

Question 21

Describe phagocytosis - internalized

Answer 21

Pathogen internalized in large membrane enclose endocytic vesicle = phagosome (goes into vesicle)

Question 22

Describe phagocytosis - fusing

Answer 22

Phagosome fuses with one or more lysosomes —> phagolysosome = lysosomal contents released

Question 23

Describe phagocytosis - kill

Answer 23

Ph drops and killed
Phagolysosome acidity’s = acquires antimicrobial peptides and enzymes to kill pathogen
Activated enzymes at low ph and chops up bacteria

Question 24

Describe neutrophils - phagocytosis

Answer 24

Contain dif types of cytoplasmic granules = primary granules and secondary granules

Question 25

What do granules of neutrophils do

Answer 25

Fuse with phagosome (phagolysosome) and release additional enzymes and antimicrobial peptides that attack the microorganism

Question 26

How are neutrophils diff from other cells

Answer 26

Macrophages and dendritic cells do not have granules

Question 27

What happens when Ligand binding/phagocytosis

Answer 27

Triggers signalling and results in change

Question 28

What do phagolysosomes contain

Answer 28

Products that can kill microbes

Question 29

Name products that phagolysosomes contain

Answer 29

Low ph/acidification Hydrologic enzymes from lysozymes and proteases, love low ph Oxidative attack Antimicrobial peptides = defensins, Catholicidin

Question 30

What is oxidative attack

Answer 30

Employs reactive oxygen species = ROS and reactive nitrogen species = RNS = add more oxygen or nitrogen = toxic to pathogen phagocytosed = damage microbial membranes and intracellular components

Question 31

How are ROS generated

Answer 31

Free radicals = ROS Generated by phagocytes unique NADPH oxidase enzyme complex - or phagosome NADPH oxidase

Question 32

What does ROS production do

Answer 32

By NADPH oxidase increases oxygen consumption —> respiratory burst

Question 33

T OR F phagolysosome only important organelle for innate immunity

Answer 33

FALSEEEEEEEE Important organelle for innate and adaptive immunity

Question 34

How is phagolysosome important organelle for innate immunity

Answer 34

Pathogen killing Pathogen processes Pathogen presentation to sensory cytoslic PRRS (some inside cells, tlr, nods)

Question 35

How is phagolysosome important organelle for adaptive immunity

Answer 35

Antigen degreadtion Antigen processing Antigen presentation onto mhc molecules

Question 36

What can phagocytes do

Answer 36

Clear cells have that undergone apoptosis Dead/dying cells express damps —> eat me signals, bind to prrs

Question 37

What do some healthy cells express

Answer 37

Do not eat me signals = CD47

Question 38

Describe CD47

Answer 38

Will bind to signal regulatory protein alpha (SIRPalpha) on macrophage = transmits signals that inhibit phagocytosis

Question 39

WHAT DO TUMOUR CELLS EXPRESS

Answer 39

Elevated levels of CD47 —> tumour progression Novel therapy = antibodies to block CD47 on tumour cells —> hopefully macrophage an phagocytose cancer cell

Question 40

DESCRibe neutrophils

Answer 40

Another cell capable of phagocytosis = inject and kill microorganisms Not tissue resident = in circulation, recruited to site of infection

Question 41

What can neutrophils do

Answer 41

20-60% of neutrophils can produce extra cellular matrix called nets = neutrophil extracellular traps —> trap microorganisms and prevent spread

Question 42

What is pus

Answer 42

Result of dead and dying neutrophils

Question 43

Describe whole process of nets

Answer 43

Pamp binds prr = signals from prrs activate neutrophils = leads to intracellular signalling Degradation of intracellular membrane of neutrophils then chromatins decondense Cell bursts open and nets released = chromatins attached to some peptides Nets can trap micoorganisms, stops spread

Question 44

Compare nets to reg cell

Answer 44

10-15x longer than actual cell

Question 45

Describe homeostasis - cns resident microglia

Answer 45

Cns resident microglia = macrophages of Brain responsible for establishing proper neuronal connections = Participate in debris clean up, brain dev, memory, learning

Question 46

Describe disease multiple sclerosis

Answer 46

Not in homeostasis Complex inflammatory disease characterized by myelin breakdown = lots of toxic debris built up in brain lesion micro environments

Question 47

What is required for cns repair

Answer 47

Microglia and peripheral infiltrates of macrophages participate in debris clean up —> various animal models show that this is required for cns repair Helps homeostasis

Question 48

Describe receptor binding - microglia

Answer 48

Recognition of cell debris by mouse microglia via receptors leading to pseudopodia Receptor binding important for initiating phagocytosis If recpetor KO microglia = no pseudopodia formed

Question 49

Describe measuring phagocytosis in vitro

Answer 49

We want to know impact of diff conditions on phagocytosis Dye substrate with a ph sensitive fluorophore —> only fluoresces under low ph conditions = phagolysosome Fed substrate to macrophage s Measured fluorescence of macrophages before and after diff condition

Question 50

Describe key points from research ex

Answer 50

Multiple steps involved in phagocytosis Diff things may be affected if one step goes wrong, depends which