Lec 4 phagocytosis

Question 1

What is phagocytosis

Answer 1

the process of ingestion or engulfment and destruction of foreign particles such as bacteria and dead cells by the phagocytic cells.

Question 2

What are phagocytes

Answer 2

white blood cells that protect the body by ingesting(phagocytosing) harmful foreign particles , bacteria and dead or dying cells.

Question 3

Which cells are professional phagocytes

Answer 3

Neutrophils
Monocytes
Macrophages
Dendritic cells
Mast cells

Question 4

What cells are non professional phagocytes?

Answer 4

Fibroblasts

Osteocytes

Question 5

What is the function of fibroblasts?

Answer 5

Phagocytose collagen in the process of remolding scares`

Question 6

Which professional phagocytes are found in the blood?

Answer 6

Neutrophils

Monocytes

Question 7

Which professional phagocytes are found in the Bone marrow?

Answer 7

Macrophages

Monocytes

Question 8

Which professional phagocytes are found in the gut and intestinal peyer’s patches?

Answer 8

Macrophages

Question 9

Which professional phagocytes are found in the skin?

Answer 9

Dendritic cells
Conventional macrophages
Mast cells

Question 10

What are the steps/stages of phagocytosis?

Answer 10

1. Migration / Margination / Diapedesis
2. Chemotaxis
3. Adherence / attachment
4. Ingestion / engulfment
5. Destruction of the microbe (killing process)

Question 11

What is meant by migration?

Answer 11

migration of leucocytes and phagocytes from the venules to the tissues(site of infection)

Question 12

What do the macrophages produce during migration?

Answer 12

cytokines ,TNF-alpha and IL1

Question 13

What is the function of cytokines ,TNF-alpha and IL1

Answer 13

activate the endothelial cells of the nearby venules to produce adhesion molecules(selectins) and chemokines.

Question 14

What does activation of selectins and chemokines result in?

Answer 14

Margination - adherence of leucocytes to the endothelium

Question 15

What else to cytokines ,TNF-alpha and IL1 mediate ?

Answer 15

Diapedesis - migration of leucocytes and monocytes from the blood through the endothelial wall of blood vessels to the tissues

Question 16

What occurs In margination?

Answer 16

Selectins cause leukocytes to adhere to blood vessel walls

Question 17

What occurs In diapedesis/ emigration?

Answer 17

Leukocytes squeeze between endothelial cells into tissue space

Question 18

What is chemotaxis

Answer 18

Attraction of neutrophils and macrophages to the site of infection.

Question 19

What is chemotaxis mediated by

Answer 19

chemotactic substances liberated from microbes and damaged tissues

Question 20

What are some examples of the chemotactic substances liberated from microbes and damaged tissues

Answer 20

• Serum complement C5a,C3a
• Interleukin 8 (IL8)
• Leukotrienes(cytokines)

Question 21

What is attachment of phagocytes to the microbe mediated by?

Answer 21

• Common phagocytic receptors( PRRs such as Toll-like receptors, scavenger receptors etc.…)
• Specific Opsonin receptors (Fc receptor for IgG and the complement receptors for C3b,iC3b and C4b)

Question 22

Where are the attachment receptors expressed?

Answer 22

on surface of phagocytic cells

Question 23

What do the attachment receptors attach?

Answer 23

They attach PAMPs expressed on microbes (and not on host cells)

Question 24

What is the function of the scavenger receptors in phagocytosis?

Answer 24

Bind to many microbial ligands (LPS, LTA, etc)

Question 25

What is the function of the macrophage mannose receptors in phagocytosis?

Answer 25

Bind to mannose-containing microbial carbohydrates

Question 26

What is the function of the B-glucan receptors in phagocytosis?

Answer 26

Bind to glycan in microbial cell walls

Question 27

What are the opsonin receptors?

Answer 27

1. Complement receptors | 2. Immunoglobulin Fc receptors

Question 28

What is the opsonin on complement receptors?

Answer 28

C3b or its cleavage products

Question 29

What is the opsonin on immunoglobulin Fc receptors?

Answer 29

antibody

Question 30

What occurs in the ingestion / engulfment ?

Answer 30

1/ phagocyte extends pseudopods around the microbe 2. These fuse and the organism is included into a vacuole called phagosome. 3. Lysosomal granules then fuse with the phagosome forming the phagolysosome.

Question 31

What are the mechanisms of intracellular killing?

Answer 31

Oxygen dependent mechanism | Oxygen independant mechanism

Question 32

What occurs in the oxygen dependant mechanism?

Answer 32

1. Formation of the phagosome 2. Increase in the activity of NADPH phagosome oxidase 3. Increased oxygen consumption with an increased formation of ROS - RESPIRATORY BURST 4. NADPH utilized to reduce molecular oxygen bound to cytochrome causes a burst of O2 consumption 5. As a result, O2 is converted to superoxide anion, hydrogen peroxide singlet oxygen, and hydroxyl radicals (all of which are powerful microbial agents)

Question 33

What are the most important toxins in the oxygen dependant mechanism?

Answer 33

1. superoxide anion 2. nitric oxide 3. hydrogen peroxide

Question 34

What occurs in the O2 independent process of intracellular killing?

Answer 34

1. Phagosome fuses with lysosome and creates a phagolysosome 2. Lysosomal enzymes kill most bacteria within 30 mins 3. Digestion occurs

Question 35

What are some examples of the lysosomal enzymes which kill bacteria during O2 independent intracellular killing?

Answer 35

- Lysosome : destroys cell wall peptidoglycan - Lipases and proteases - RNAses and DNAses - Lactoferrins present in neutrophil granules remove essential iron from bacteria

Question 36

What occurs after digestion during O2 independent intracellular killing?

Answer 36

residual boy with undigestable material is discharged

Question 37

What are additional killing factors during O2 independent intracellular killing?

Answer 37

- increased glycolysis renders the medium acidic (ph 4) by its end product (pyretic acid) - this is bactericidal to most bacteria

Question 38

What do lysozyme and lactoferrins act as in the O2 independent mechanisms?

Answer 38

they act as bacteriostatic substances, which are O2 independent and function under anaerobic conditions

Question 39

What is the final step in O2 independent intracellular killing?

Answer 39

Hydrolytic enzymes digest the killed organisms and the degraded products are released to the exterior