Immunology 10 - Phagocytosis
How can you tell older neutrophils apart from less developed ones?
The older the neutrophil, the more segmented the nucleus
What role do opsonins play in phagocytosis?
They act like ketchup, ease phagocytosis
When do band neutrophil appear?
They are less developed, and so appear only in times of overwhelming need
What is one important thing to remember about phagocytes?
They are messy eaters, and ROS can spill out and damage local tissue
Why do neutrophils die quickly?
They constantly generate toxic oxygen species
What capabilites do mast cells have?
They have TLRs, can interact with B and T cells They can also present antigens but their role is not well understood
What happens once neutrophils leave the blood?
They work as much as possible before dying and becoming pus
What intracellular proteins facilitate phagocytosis?
actin and myosin
What are some ways that pathogens avoid phagocytosis?
avoiding contact avoid engulfment using sugar capsules survive inside phagocyte kill phagocyte disrupt cell signalling
What protein is associated with caveolae lipid rafts?
caveolin (from a picture)
What are the steps of leukocyte extravasation?
chemoattraction (smells a chemical signal) rolling adhesion tight adhesion transmigration
What are the four types of endocytosis?
clathrin -mediated caveolae Macropinocytosis phagocytosis
What does myeloperoxidase do? Where is it stored in neutrophils?
contained in neutrophil granules creates hypochloride (bleach) to kill pathogen
What is the process a leukocyte goes through to escape a blood vessel?
diapedesis
What are the functions of endocytosis?
engulf polar molecules nutrient uptake growth pathogen entry neurotransmission
What types of cells are nonprofessional phagocytes?
fibroblasts epithelial cells endothelial cells mesenchymal cells immature cells
What type of bacteria do mast cells prefer to consume? What do they specialize in?
gram negative, specialize in processing fimbrial proteins
What kind of cells activate macrophages?
helper T cells using IFN- gamma
what structures do caveolae form once inside the cell?
lipid rafts
What methods do macrophages have to destroy pathogens?
lysosomes Respiratory burst
What functions are associated with macropinocytosis?
non-selective endocytosis of soluble macromolecules may facilitate antigen presentation may be way for pathogens to enter cell
What differentiates nonprofessional phagocytes from professional?
nonprofessional do not have efficient phagocytic receptors Non-pro also don't produce ROS
How is endocytosis accomplished?
part of the plasma membrane is invaginated and pinched off, forming a membrane bound vesicle - *endosome*
What kind of material can be phagocytosed?
pathogens, nutrients, minerals, cell debris
What is phagocytosis?
process of endocytosis whereby solid/larger particles are engulfed by membrane, forming a phagosome.
What is the goal of the respiratory burst?
produce oxidizing agents that can be used to kill bacteria
What do caveolae contain?
protein, cholesterol
How are LDL and iron transported into the cell?
receptor-mediated endocytosis
What kind of membrane proteins (apart from clathrins) are necessary for clathrin-mediated endocytosis?
receptors specific to the molecules being internalized
What are the two oxygen dependent ways of killing bacteria?
superoxide myeloperoxidase
How do mast cells contribute to inflammation?
they produce cytokines that chemoattract more phagocytes
How long do neutrophils live in the blood?
~5 days
How long does it take for monocytes and macrophages to reach the site of infection?
20-40 hours
How fast can neutrophils reach the site of an infection?
30 minutes
What kind of cells use endocytosis?
All nucleated cells
What are the two types of micropinocytosis?
Clathrin mediated, caveolae
Describe the timeline of an infection and how neutrophils play into the immune response
Early infection - bacteria and nearby macrophages release chemotactic signals Neutrophils follow the chemotactic signals TLRs on Neutrophils allow them to recognize pathogens, bind PAMP Phagocytose and degrade pathogen
What are the four methods of oxygen-independent intracellular killing? Describe each a little bit
Electrically charged proteins - damage bacterial membrane Lysozyme - break down cell wall Lactoferrins - (neutrophils) remove essential iron proteases and hydrolytic enzymes - digest bacterial proteins
Why does pus appear to be green?
Heme pigment in myeloperoxidase
What does the cell membrane look like in areas that perform pinocytosis?
Highly ruffled
What is a respiratory burst? What cells does this occur in?
Increase in O2 consumption when a neutrophil ingests bacteria or other material
Compare the respiratory burst of neutrophils and macrophages
Macrophages are much more effecient, and so are usually found more at sites of chronic inflammation (they last longer)
What kind of phagocytic activity do nonprofessional phagocytes have?
Nonprofessional phagocytes can phagocytose without receptors under certain conditions
Describe the two methods of phagolysosome formation in a phagocyte.
Oxygen dependent - NADPH mediates production of reactive oxygen species Oxygen independent - release granules containing proteolytic enzymes
What is endocytosis?
Process by which cell engulfs some extracellular fluid containing some material
What are the professional phagocytes? What does this mean for their phagocytic activity?
Professional phagocytes have receptors for pathogens. They are: Neutrophils Mono/macs/dentritic mast cells Basophiles/eosinophils