Phagocytosis Flashcards Preview

Immunology > Phagocytosis > Flashcards

Flashcards in Phagocytosis Deck (20)
Loading flashcards...
1

Phagocytosis

A specialised process by which particulate matter (>1um) is internalised

First observed by Eli Metchnikoff in 1883

2

Stages of phagocytosis

1. Recognition
2. Ingestion
3. Digestion

3

Recognition - direct binding

Direct binding occurs when molecular components on the surface of microbes directly bind to phagocytes

The molecular components are called PAMPs and include things such as LPS

PAMPs are recognised by PRRs

DAMPs can also be recognised, these are altered self proteins

4

Recognition - indirect binding

Indirect binding occurs when proteins that have already bound to the microbes are recognised by the phagocyte

These tend to be opsonins

The most effective opsonins are produced by the complement system

5

C-type lectin receptors

These PRRs bind carbohydrates on extracellular pathogens

-Mannose receptor
-DC-SIGN
-Dectin-1

6

Scavenger receptors

These PRRs bind altered self molecules

-SR-A
-SR-B

7

TLRs

TLRS recognise a wide variety of PAMPs and DAMPs

They activate different signalling pathways to stimulate the production of type I interferons and inflammatory mediators

8

Type I interferons

Inhibit the replication of viruses

9

Mannose receptor

Expressed on most macrophages and dendritic cells

Binds mannose, fucose and a-mannan

Has 8 extracellular domains

Triggers internalisation of the pathogen

10

Dectin-1

Expressed on a variety of myeloid cells

Binds B-glucans

Triggers MAPK pathways which induce the expression of inflammatory mediators

11

SR-A

Expressed on all macrophages and some endothelial cells

Binds modified LDL

12

SR-B

Expressed on endothelial cells, dendritic cells, platelets, macrophages and monocytes

13

NOD-like receptors

Cytoplasmic PRRs

Trigger autophagy (self-eating)

14

Rig-like receptors

Cytoplasmic PRRs

Detect viral replication and induce the production of anti-viral cytokines

15

TLR4

TLR4 is known for binding LPS

This upregulates the transcription of TNF-a

If this occurs in the blood, it can lead to septic shock

16

Opsonins

Opsonins coat microbes and make them more attractive to phagocytes

They can be antibodies, complement proteins and lectins

17

Ingestion

Ingestion is initiated by receptor clustering

Pseudopodia surround the particle and fuse it into a phagosome

This requires a significant amount of energy and cytoskeletal rearrangement

18

Oxygen-independent digestion

-Acidification = protons are pumped into the phagolysosome
-Lysozyme
-Enzymes
-Defensins = form pores in cytoplasmic membranes
-Lactoferrin = bind to essential nutrients to inhibit microbial growth
-Cationic proteins = active at alkaline pH, damage microbial membranes

19

Oxygen-dependent digestion

-Respiratory burst
-Nitric oxide

20

NETosis

A mechanism exclusive to neutrophils

A net-like chemical is secreted to trap nearby pathogens

Secretion of the net causes cell death; the net traps the pathogen in the hope another phagocyte will detect and deal with it