Phagocytosis

Question 1

What are the roles of phagocytosis? [3 marks]

Answer 1

• Protection from pathogens
• Disposal of damaged/dying cells
• Processing ad presentation of antigens

Question 2

Types of phagocytes from the myeloid lineage? [6 marks]

Answer 2

• Neutrophils
• Macrophages
• Dendritic cells
• Mast cells
• Eosinophils
• Basophils

Question 3

Types of phagocytes from the lymphoid lineage? [1 mark]

Answer 3

NK cells

Question 4

What is the most abundant white blood cell circulating in blood? [1 mark]

Answer 4

Polymorphonuclear neutrophils

Question 5

What are the enzymes present in neutrophils? [3 marks]

Answer 5

• Lysozymes
• Collagenase
• Elastase

Question 6

Where are dendritic cells found? [3 marks]

Answer 6

• Skin
• Mucosa
• Tissue

Question 7

How do dendritic cells work? [2 marks]

Answer 7

• Capture microbes and phagocytose them by forming a network

- They present antigens to T cells

Question 8

What are the antigens on DCs recognised by? [1 marks]

Answer 8

T cell receptors

Question 9

What gets co-stimulated by CD28 from T cells? [1 mark]

Answer 9

CD80/CD86

Question 10

What are the steps on phagocytosis? [4 marks]

Answer 10

• Chemotaxis
• Recognition and attachment to microbes/dead cells
• Engulfment
• Killing/digestion of ingested microbe/dead cells

Question 11

What are chemoattractants released by? [4 marks]

Answer 11

• Bacteria
• Inflammatory cells
• Damaged tissue
• Complement proteins

Question 12

What do Toll-like receptors recognise? [5 marks]

Answer 12

• Gram positive and gram-negative bacteria
• Bacterial DNA sequences
• Viral RNA
• Glucans in fungi

Question 13

What roles do Toll-like receptors do? [2 marks]

Answer 13

• Stimulates production of inflammatory cytokines

- Essential roles in innate immunity

Question 14

What type of receptors are mannose receptors? [1 mark]

Answer 14

C-type lectin receptors

Question 15

How do NOD-like receptors (NLRs) reside? [1 mark]

Answer 15

As free proteins in cytoplasm

Question 16

How do RIG-like helicase receptors (RLRs)? [1 mark]

Answer 16

Cytosolic receptor for viral dsRNA

Question 17

What are scavenger receptors important for? [1 mark]

Answer 17

Disposal of dead/damaged cells

Question 18

What is opsonisation? [3 marks]

Answer 18

• Coating of microbes with opsonin
• Complement proteins and antibodies
• Makes phagocytosis easier

Question 19

Why do encapsulated microorganisms need opsonisation for phagocytosis? [1 mark]

Answer 19

Because the capsule rejects phagocytosis

Question 20

What happens in engulfment? [4 marks]

Answer 20

• Actin cytoskeleton is rearranged to grow around the pathogen.
• Pseudopods form about the pathogen and the plasma membrane of the phagocyte remodels
• Phagolysosome forms
• Pathogen is the destroyed by enzymes

Question 21

What are the different types of lysosomes? [4 marks]

Answer 21

Cathepsin: degrade microbe
Lysozyme: break bacterial walls
Lactoferrin: binds irons so that there’s not enough for bacterial growth
Defensins: destroy bacterial walls

Question 22

How are free radicals formed? [3 marks]

Answer 22

• Superoxide anion made from oxygen

- NOs and ROS radicals formed from water and superoxide

Question 23

How do pathogens block phagocyte attachment? [1 mark]

Answer 23

By capsules

Question 24

How do pathogens block destruction? [2 marks]

Answer 24

• Resistance to ROS

- Blocks phagosome-lysosome fusions

Question 25

How do pathogens kill phagocytes? [1 mark]

Answer 25

Produce toxins

Question 26

What is the difference between phagocytosis of a pathogen and phagocytosis of an apoptotic cell? [1 mark]

Answer 26

There is no inflammation in the phagocytosis of apoptotic cells.

Question 27

What do phagocytes do when they take up apoptotic cells? [2 marks]

Answer 27

• Secrete pro-healing cytokines

- Present self-antigens