5- Phagocytosis Flashcards
What is phagocytosis?
The ability of some cells to ingest foreign particles, literally “eating by cells”
What are the two ‘professional phagocytes’ and briefly describe their roles.
Neutrophils: first to accumulate around the invaders and initiate the phagocytic process- suicide bombers
Macrophages: migrate to the tissue site and initiate phagocytosis- serial killers
List the steps of phagocytosis and briefly describe each.
1) Chemotaxis: delivery of phagocytic cells to the site of infection
2) Adherance: Phagocytic adherence to the target
3) Ingestion: Engulfment of the target particle
4) Destruction: Intracellular killing and digestion of the target
** Egestion only in the case of macrophages
What are the 4 components stored in primary granules?
1) Hydrolases
2) Lysozyme
3) Defensins
4) Myeloperoxidase
What is the role of hydrolases in primary granules?
Breaks covalent bonds by adding water, important for degrading dead bacteria or dead tissues
What is the role of lysozyme in primary granules?
Breaks down peptidoglycan in gram-positive bacteria, found in many secretions of the body
What is the role of defensins in primary granules?
Small cationic proteins that kill bacteria, especially gram-positive
Aka antimicrobial peptides
Form a barrel shape around the bacteria and punches holes in it
What is the role of myeloperoxidase in primary granules?
An enzyme that has an important role in the oxygen mediated killing mechanism
What makes up the contents stored in secondary granules?
1) Lysozyme
2) Lactoferrin
3) Collagenase
What is the role of lysozyme in secondary granules?
Breaks down peptidoglycan in gram-positive bacteria, found in many secretions of the body
What is the role of lactoferrin in secondary granules?
chelates iron- bacteria need iron for survival
What is the role of collagenase in secondary granules?
degrades connective tissue, so it can move through to the site of inflammation
What is opsonization?
Coating of positively charged material on a pathogen so a neutrophil can bind to and kill it
Both pathogens and neutrophils are negatively charged, so they naturally repel each other without opsonization
What is a phagosome?
Membrane-bound vesicle containing the ingested microbe or material in the process of phagocytosis
What are the two neutrophil membrane receptors that ard important in phagocytosis?
Fc receptors- bind antibody that is bound to an antigen, especially IgG antibody
C3b receptors- bind to C3b when it is coating bacteria, etc
Once neutrophils bind to opsonized material, it is readily engulfed, forming a ________.
Phagosome
What is a phagolysosome
Formed when the membranes of the phagosome and lysosome actually fuse resulting in a digestive vacuole called the phagolysosome, other lysosomes will continue to fuse as well
Where does the killing and digestion of the engulfed microbe take place?
Phagolysosome
What is the most potent killing mechanism of a neutrophil?
Oxygen mediated killing mechanism
What are the killing products used in the oxygen mediated killing mechanism?
Hypochlorite
Hydrogen peroxide
Aldehydes
Oxygen radicals
What is the fate of neutrophils after killing a pathogen?
Neutrophils die and lyse after extended phagocytosis, killing, and digestion of bacterial cells
***This makes up the main component of pus
What is the fate of macrophages after killing a pathogen?
Macrophages egest (discharge) digested debris and allow insertion of microbial antigenic components into the plasma membrane for presentation to lymphocytes in the immunological response
What is the difference between M1 and M2 macrophages?
M1- phagocytic cells like neutrophils
M2- clean up the mess
What are the first cells attracted to sites of inflammation?
Neutrophils
Cytokines activate _________ _________ _________ so that neutrophils in the bloodstream will stop, attach, and then migrate toward the sites of microbial invasion and tissue damage
vascular endothelial cells
_________ bind, phagocytose, and kill invading microorganisms.
Neutrophils
Microorganisms must usually be __________ before the can be efficiently ingested and killed.
opsonized
What are the two most effective opsonins?
antibodies and complement
Ingested microorganisms are killed by potent oxidants through a process called the ______ _______, by antibacterial proteins called _______ and by _______ _______.
Respiratory burst
defensins
lytic enzymes
Can neutrophils undertake multiple phagocytosis?
no
_______ migrate to sites of inflammation after neutrophils.
Macrophages
they eat and kill any surviving microbial invaders
Macrophages also eat dead and dying neutrophils thus preventing what?
Damage caused by escaping neutrophil enzymes
Which cells begin the healing process in damaged tissues?
Macrophages
Macrophages are essential antigen-presenting cells for adaptive or innate immune system?
Adaptive
