Phagocytosis and Phagosome maturation

Question 1

What is phagocytosis?

Answer 1

An ‘eating-cell-process’.

• It is part of the innate immune response.
• It involves ingesting foreign material with the use of phagocytes.

Question 2

Why do we need phagocytosis?

Answer 2

To clear pathogens and to maintain tissue homeostasis and remodelling.

Question 3

How was phagocytosis initially studied?

Answer 3

A russian zoologist identified phagocytic cells through looking at amoebae and how they feed.
- He characterised different cells based on their nuclear morphology.

Question 4

What was a key finding which led to a Nobel prize?

Answer 4

Found that pre-stimulated macrophages respond differently to the pathogen.

Question 5

What are the 4 main stages of phagocytosis and phagosome maturation?

Answer 5

1. Target recognition.
2. Engulfment.
3. Destruction.
4. Waste disposal and antigen presentation.

Question 6

Describe the process of phagocytosis and phagosome maturation.

Answer 6

1. The phagocyte attaches to the pathogen via receptors.
   - The plasma membrane begins to surround the pathogen.
2. The phagocyte membrane engulfs the pathogen, forming a phagosome.
3. The phagosome fuses with a lysosome to make the intracellular compartment inhabitable for the pathogen.
   - Forms a phagolysosome.
4. The pathogen is digested and pieces are displayed to T cells on the surface of the cell via MHC molecules.
   - The bacterial debris is disposed of through egestion.

Question 7

What are the 2 forms of target recognition and what are they involved in?

Answer 7

1. Direct
   - Recognition of the pathogen surface PAMPs via PRRs.
2. Indirect
   - Recognition of host factors (complement or antibodies).
   - This is helped by opsonising factors.

Question 8

In direct recognition, what are the main PAMPs recognised by macrophages?

Answer 8

Mannose receptor, scavenger receptors and dectin-1 (glucan receptor).