Phagocytosis

What is the idea behind the zipper hypothesis?

The particle must be opsonized (coated) completely to be ingested, by actin-based pseudopods, who extend via polymerization. * igG * Complement

How do the early/late endosomes become more acidic?

There are more ATPases as you go from early to late endosome to lysosome

What question did the zipper hypothesis ask?

They wanted to see if uptake of a particulate is specific/specialized

What is good about Fc receptors?

Used to tackle multiple bacteria

Why does listeria have a double membrane?

When it goes to the neighboring cell (engulfment) it picks up the double membrane

Why must HBP find a way to mask the cholesterol on itself?

accumulation of cholesterol in bacterial membranes facilitates uptake and killing by macrophages and T cells

What does cytochalasin inhibit?

actin

Extension of the psuedopods requires what?

actin polymerization

What are pseudopods?

actin-based, move along IgG to completely coat what the phagocyte is about to ingest.

How do mucosal cells inhibit H.B. pylori? They stop the bacteria from?

bacterial cell wall synthesis

What does HBP need for survival?

cholesterol

What does Helicobacter pylori do?

colonizes surface of the gut

How is listeria monocytogenes shigella taken up?

complement receptors into macrophages, goes into intracellular vesicles and breaks out.

What does respiratory burst result in?

formation of reactive o2 metabolites for pathogen killing

Phagocytes of the brain

glial cells

Where is helicobacter pylori not found?

in the deeper regions of gastric mucosa.

IgG process:

mediated by Fc receptors, and uses a common trigger to evoke a response (trigger response), or can be specific (IgG) ? *Ask Steven

Phagocytes of the skin

melanocytes/dendritic cells

Does compliment have an inflammatory response?

no

Who does listeria monocytogenes shigella effect?

pregnant women, children, elderly because they are immunocompromised

How do the surface gastric mucosal cells prevent infection by HB. pylori?

secrete these particular antigens, unusual mucins that prevent the growth and motility of H. pylori O-linked sugars,sticky, first line of defense

What is phagocytosis

uptake of particulates, they are insoluble, and the membrane extends around the particle: not homogenous

What is the effect of H. pylori encoding of cholesterol-alpha-glucosyltransferase?

1. prevents uptake of bacteria (by macrophage) 2. promotes colonization

Why would a pathogen invade a macrophage?

1. removal from immune system 2. don't need special entry system * if the pathogen is NOT in the circulatory sys, the macrophage won't develop an immune response against it.

Which forms of pathogen uptake are receptor mediated?

1. zipper hypothesis: receptor: igG bound to Fc 2. trigger hypothesis: receptor: psuedopod recognition of bacteria trigger 3. Compliment

What is the idea behind the trigger hypothesis?

Bacteria inject molecules (trigger) into the phagocyte cytoplasm which triggers an extensive membrane ruffling near the bacteria. The ruffles/pseudopods fold up and engulf the bacteria in an actin-based macropinosome

How did HB. Pylori response to mucin secretion by surface gastric mucosal cells?

Cholesterol glucosylation, that promotes immune evasion! * encodes a cholesterol-alpha-glucosyltransferase * puts a carb on a lipid or sterol, so macrophage cannot recognize it and bacteria sneak in and colonize.

Using lipids how can a pathogen evade a macrophage?

Coated with lipids that are not degraded in lysosmes, so they live in the lysosome but cannot secrete any proteins/antigens, or else they'll be detected...so they store them near themselves.

How does trigger hypothesis differ from both complement and zipper?

Complement and zipper both form a tightly opposed membrane, but trigger you get a spacious phagosome.

How is listeria monocytogenes shigella taken up?

Food born pathogen found in milk.

What is respiratory burst triggered by?

IgG opsonized targets - makes sense bc IgG does an inflammatory response. * This is why complement--no igG : no respiratory burst. Does this mean the trigger hypothesis uses igG? since there is respiratory burst associated with it?

How do IgG and compliment differ?

IgG: pseudopods extend out Complement: particulates combined and then sink in. * both need actin * both ex. of zipper hypothesis

What is scary about listeria monocytogenes shigella

It does not evoke an immune response, except for the initial flu symptoms

Phagocytes of the liver

Kupffer cells

What directs the extension of the pseudopods?

Ligands do, "like a zipper"

What is the rate determining step of respiratory burst?

NADPH Oxidase

Types of phagocytes in the blood

Neutrophils and Monocytes

How can a pathogen interfere with the acidification of a phagosome?

Pathogens can take off the ATPase, making the vesicle smooth, and as a result live in a neutral pH environment

Listeria

Phagocytosed by zipper mechanism/complement

What is an example of a pathogen that has hijacked the compliment pathway?

TB

What is an example of a pathogen that interferes with the acidity of a phagosome?

Tb hangs out in an early endosome, it prevents acidication by taking off the ATPases.

How is uptake of less innocuous material done?

1. debris (complement receptors) - by cells that are dead or dying 2. senescent cells (phosphatidyl serine receptors) 3. no inflammatory response

Once a pathogen has invaded a macropage, what are it's defense strategies?

1. escape to cytoplasm 2. interfere with acidification of phagosome 3. interfere with oxidative burst 4. survive in lysosome 5. interfere with vesicular trafficking

Which forms up uptake require are inhibited by cytochalasins?

1. igG: zipper hypothesis 2. Trigger Hypothesis 3. Complement

The binding of Fc receptors to IgG results in what?

1. inflammatory response 2. chemotactic factors 3. reactive O2 species 4. cytokines (gene regulation)

What are three mechanisms pathogens use to evade detection/consumption?

1. Escape ie. Listeria (rockets) 2. Prevent fusion with lysosomes (Salmonella) 3. Survive in the Phagolysosme (lipid coats)

What is the process of respiratory burst

1. NADPH oxidase takes molecular O2 and generates H+ and superoxide radical. 2. Super Oxide Dismutase SOD, takes super oxide and turns it into H2O2 very rapidly, it oxidizes everything and is short-lived 3. Optional --> some phagocytes (neutrophils) express myeloperoxidase (MPO) that takes chloride and H2O2 and makes hypochlorous acid (bleach)

What do endocytosis and phagocytosis have in common?

1. Receptor-mediated and Target binds receptor on phagocyte cell surface(S) 2. Psuedopods surround particle (D) 2. Delivery to lysosome (phagolysosome) 4. Ultimate Fate: Residual Bodies of the lysosome

How does listeria monocytogenes shigella work?

1. Taken up by complement receptors into macrophages 2. Goes into intracellular vesicles and breaks out 3. Has enzymes that dissolve the membrane, and goes to cytosol (initial flu symptoms 4. Divides + hijacks actin polymerization machinery 5. Makes comet tails and shoots out of one cell, into the next 6. 2 membranes, two enzymes

4 Qualities of Endocytosis

1. clathrin mediated 2. 50 nm vesicles 3. All cells do it 4. Homogeneous

What test could you do to see if uptake was by endocytosis or phagocytosis?

Phagocytosis requires actin, where as endocytosis requires a clathrin coat. You could treat cells with cytochalasin (inhibits actin), if there is still uptake it is endocytosis, if there is no uptake it is phagocytosis.

Phagocytes of the eye

Pigmented epithelium

Results of Zipper Hypothesis?

Pseudopods extend only as far as the igG receptor, it is specialized, not just a cap/trigger.

How do pseudopod movement differ from receptor mediated endocytosis?

Pseudopods require actin, receptor mediated endocytosis happens via clathrin, which is self-assembly due to triskelions.

What is an example of a pathogen that undergoes trigger hypothesis

Salmonella

How was the zipper hypothesis tested?

Saw that IgG bound to the particulate bound to Fc receptors on the pseudopods, and extension occured (via actin polymerization) only as far up as there was igG.

IgG on a pathogen does what?

Signals to the cell that it is foriegn, and Fc receptors bind to it.