Phagocytosis and Opsonisation Flashcards
What is pinocytosis?
A mechanism by which cells can “drink” liquid from outside
What cells use pinocytosis
All cells
List the four phagocytes.
Neutrophils
Monocytes
Macrophages
Dendritic cells
Explain how phagocytosis occurs.
The target adheres to the surface of the phagocyte
The phagocyte engulfs the microbe and encloses it within a membrane-bound vesicle known as a phagosome
The phagosome fuses with a lysosome, an organelle that contains digestive enzymes
Whatever indigestible material remains is exocytosed
What engulfs the microbe during phagocytosis?
A phagosome engulfs the microbe
What is the phagosome?
a membrane-bound vesicle
What does the phagosome fuse with?
A lysosome
What is a lysosome?
An organelle that contains digestive enzymes
What digests captured materials in the phagosome?
Lysosomal enzymes
What happens to the materials that are digested in a phagosome?
They are released from the cell
What is the resulting organelle called when a phagosome fuses with a lysosome?
Phagolysosome
What are the six different ways that a phagolysosome can kill microbes?
Acidification
Toxic oxygen-derived products
Toxic nitrogen oxides
Antimicrobial peptides
Enzymes
Competitors
Name some of the toxic oxygen-derived products used to kill microbes during phagocytosis.
(2)
Hydrogen peroxide (H2O2)
Hydroxyl Radical (OH.)
Name a toxic nitrogen oxide that can be used to kill microbes during phagocytosis.
Nitric oxide (NO)
Name two antimicrobial peptides used to kill microbes during phagocytosis.
Defensins
Cationic proteins
Name three enzymes used to kill microbes during phagocytosis.
NADPH-dependent oxidases
Lysozyme
Acid hydrolases
What does NADPH-dependent oxidases do?
It generates toxic oxygen derivatives
What does lysozyme do?
Dissolves cell walls of some Gram-positive bacteria
What does acid hydrolases do?
Further digests bacteria
Phagocytes express receptors on their cell surfaces for what five things.
Carbohydrates
Glycans
LPS
Complement components
Antibodies
Give an example of a carbohydrate found in bacteria.
Mannose is found in bacterial cell walls
Give an example of a glycans found in bacteria.
Peptidoglycan in bacterial cell walls
How do neutrophils move towards bacteria?
3
Neutrophils sense the presence of bacterial products
Neutrophils move towards them along a gradient of increasing concentration
This is called chemotaxis
Where is there a large reserve of neutrophils?
In the bone marrow
Describe how a neutrophil carries out its work.
4
Neutrophils leave their reserves in bone marrow when they are needed to fight infection
Neutrophils travel to and enter the infected tissue
Neutrophils engulf and kill bacteria
The neutrophils die in the tissue and are engulfed and degraded by macrophages
What cells engulf and degrade neutrophils?
Macrophages
What is opsonisation?
A process that greatly enhances phagocytosis where components of the immune system found in the serum make the target more attractive for phagocytosis
Describe how opsonisation works.
4
The surface of an invader is marker by proteins such as:
Activated complement components (part of the innate system)
Antibodies (part of the adaptive immune response)
Phagocytes have receptors that can bind to opsonised particles
What two things can be used to mark invadors?
Complement components
Antibodies
Explain how opsonisation by complement works.
Complement proteins in the serum are activated by the initiation of an immune response
Some of these proteins act as opsonins which facilitate receptor-mediated endocytosis of pathogens
What are opsonins?
Proteins that engage with complement receptors on phagocytes
What is endocytosis?
The taking in of matter by a living cell by pinching in of its membrane to form a vesicle
What are antibodies?
Y-shaped protein molecules produced by B cells that can identify and
neutralise pathogens
Explain how opsonisation by antibodies works.
Antibodies mark a pathogen for phagocytosis
