Phagocytosis

What do lactoferrins do? Where are they derrived?

These are from neutrophilic granules and remove essential iron from the bacteria

How does phagocytosis improve adaptive immunity?

Through preserving antigens of phagocytosed pathogen and presenting them to cells associated with the adaptive immune response (T cells).

True or false: Neutrophils have a greater activity of the oxidase system compared to monocytes

True; the hierarchy of activity is: neutrophils >> monocytes > macrophages

How is hypochlorite (bleach) formed?

When neutrophilic granules fuse with the phagolysosome, an enzyme called myeloperoxidase uses hydrogen peroxide and chlorine to create hypochlorite to kill the pathogen.

Define exocytosis

A cell's ability to export material into its environment

Define endocytosis

A eukaryotic cell's ability to take up liquid, macromolecules, and particles from its environment.

What is formed when reactive oxygen species combine to form a Phagocyte Oxidase (NADPH oxidase) complex?

A superoxide anion, which has an extra electron, making it extremely reactive. This can be used later to make hydrogen peroxide.

What does Lysozyme do?

Breaks down the cell wall and hydrolyzes the glycopeptide coating of Gram positive bacteria

How is caveolin-associated micropinocytosis different from other forms of endocytosis?

Cavioli are flask-shaped pits (about 50 nm) in a cell's membrane that increases the uptake of very small extracellular molecules, which can be used for cholesterol and lipid metabolism and cell signalling. These are abundant in the cells of the muscle, lung, fat, endothelium, and fibroblasts.

How is macropinocytosis different from other forms of endocytosis?

Cell membrane invaginations of 0.5 - 5 um which uptakes larger molecules. These larger invaginations allow for fusion with the lysosome for digestion.

What do electrically charged proteins do?

Damage the bacterial membrane

What do proteases and hydrolytic enzymes do?

Digest bacterial proteins

List oxygen independent phagocytosis mechanisms

Electrically charged proteins Lysozyme Lactoferrins Proteases and hydrolytic enzymes Enzymes in azurophilic granules (elastase and cathepsin G)

True or false: Phagocyte Oxidase (NADPH oxidase) complex is present at all times

False; the components are kept separately to prevent reactive oxygen species causing damage to endogenous cells. When a phagocyte ingests a microbe, signals that induce phagocytosis also lead to the formation of the Phagocyte Oxidase complex by combining these reactive oxygen species.

How is clathrin-mediated endocytosis different from other forms of endocytosis?

Initiated by a ligand binding to a cell-surface receptor, which causes recruitment of clathrin, which causes invagination of the membrane making pits of about 100 nm.

How are phagocytes told to start phagocytosis?

Microbe or molecules attached to microbes bind to receptors on the surface of a phagocytes, which initiate appropriate signaling cascades to start phagocytosis.

What is an opsonin?

Molecules that mark or coat targets for phagocytic cells - often through the addition of a ligand which binds to receptors on phagocytes initiating phagocytosis

What cells can undergo phagocytosis?

Neutrophils, monocytes, macrophages, and dendritic cells

Why is phagocytosis important in innate immunity?

Offers a way for the innate immune system to destroy potentially pathogenic cells quickly.

How is phagocytosis different from other forms of endocytosis?

Particles greater than 0.5 microns are taken up by the cell

What is chemotaxis?

Phagocytic cell is going to follow a chemical trail to an invading microbe

Describe the process of Phagocytosis

1. Upon finding the microbe, membrane bound receptors on the phagocyte will engage the microbe to initiate phagocytosis. 2. The microbe will be engulfed by the plasma membrane of the phagocyte to form a phagosome 3. Phagosome will fuse with a lysosome to form a phagolysosome. 4. Digestive enzymes and antimicrobial factors from lysosomes will degrade the microbe through oxygen-dependent (ROS) or oxygen-independent pathways (proteolytic enzymes) 5. Indigestible material will remain in residual body 6. This indigestible material will be exocytosed to the extracellular space

How are dendritic cells different from other professional phagocytes in how they phagocytose microbes?

Phagosomal degradation and acidification are much lower in DCs than in macrophages or neutrophils. Reduced degradation results in the conservation of antigen

What is the name of the entity formed when solid particles greater than 0.5 microns are endocytosed?

Phagosome

Why do immune cells endocytose?

Remove a pathogen from the environment Present an antigen to other immune cells Remove dead cells or debris

What is respiratory burst?

Respiratory burst refers to the increased oxygen consumption needed to ingest microbes by a phagocyte in a phagocyte oxidase complex