Phagocytosis Flashcards
What are the roles of phagocytosis? [3 marks]
- Protection from pathogens
- Disposal of damaged/dying cells
- Processing ad presentation of antigens
Types of phagocytes from the myeloid lineage? [6 marks]
- Neutrophils
- Macrophages
- Dendritic cells
- Mast cells
- Eosinophils
- Basophils
Types of phagocytes from the lymphoid lineage? [1 mark]
NK cells
What is the most abundant white blood cell circulating in blood? [1 mark]
Polymorphonuclear neutrophils
What are the enzymes present in neutrophils? [3 marks]
- Lysozymes
- Collagenase
- Elastase
Where are dendritic cells found? [3 marks]
- Skin
- Mucosa
- Tissue
How do dendritic cells work? [2 marks]
- Capture microbes and phagocytose them by forming a network
- They present antigens to T cells
What are the antigens on DCs recognised by? [1 marks]
T cell receptors
What gets co-stimulated by CD28 from T cells? [1 mark]
CD80/CD86
What are the steps on phagocytosis? [4 marks]
- Chemotaxis
- Recognition and attachment to microbes/dead cells
- Engulfment
- Killing/digestion of ingested microbe/dead cells
What are chemoattractants released by? [4 marks]
- Bacteria
- Inflammatory cells
- Damaged tissue
- Complement proteins
What do Toll-like receptors recognise? [5 marks]
- Gram positive and gram-negative bacteria
- Bacterial DNA sequences
- Viral RNA
- Glucans in fungi
What roles do Toll-like receptors do? [2 marks]
- Stimulates production of inflammatory cytokines
- Essential roles in innate immunity
What type of receptors are mannose receptors? [1 mark]
C-type lectin receptors
How do NOD-like receptors (NLRs) reside? [1 mark]
As free proteins in cytoplasm
How do RIG-like helicase receptors (RLRs)? [1 mark]
Cytosolic receptor for viral dsRNA
What are scavenger receptors important for? [1 mark]
Disposal of dead/damaged cells
What is opsonisation? [3 marks]
- Coating of microbes with opsonin
- Complement proteins and antibodies
- Makes phagocytosis easier
Why do encapsulated microorganisms need opsonisation for phagocytosis? [1 mark]
Because the capsule rejects phagocytosis
What happens in engulfment? [4 marks]
- 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
What are the different types of lysosomes? [4 marks]
Cathepsin: degrade microbe
Lysozyme: break bacterial walls
Lactoferrin: binds irons so that there’s not enough for bacterial growth
Defensins: destroy bacterial walls
How are free radicals formed? [3 marks]
- Superoxide anion made from oxygen
- NOs and ROS radicals formed from water and superoxide
How do pathogens block phagocyte attachment? [1 mark]
By capsules
How do pathogens block destruction? [2 marks]
- Resistance to ROS
- Blocks phagosome-lysosome fusions
How do pathogens kill phagocytes? [1 mark]
Produce toxins
What is the difference between phagocytosis of a pathogen and phagocytosis of an apoptotic cell? [1 mark]
There is no inflammation in the phagocytosis of apoptotic cells.
What do phagocytes do when they take up apoptotic cells? [2 marks]
- Secrete pro-healing cytokines
- Present self-antigens
