PathologyBrian Bolerjack
Inflammation and Repair45 minutos
08-26-08
1:We will talk about what the body does when cells die. Inflammation and repair involves either resolution of the infection or replacement by scar tissue. (audio doesn’t start until slide 2, so this slide isn’t verbatim)
2:Objectives: We will talk about acute and chronic inflammation, the various cells and mediators of that. And what systemic things can happen as a result of inflammatory reaction, and Thursday will be the repair process.
3:Acute inflammation is the initial type of body response to injury and dead tissue like necrosis. With acute inflammation the clinical, cardinal signs are redness (rubor), swelling (tumor), it gets warm because of increased bloodflow (calor), tender to the touch (dolor), and loss of function due to pain.
4:One of the classic ways we describe the process of acute inflammation because of clinical relevance and testability is with a myocardial infarction, because you have an organ with high oxygen demand and you get a sudden occlusion of a coronary artery due to a thrombus or plaque, and you have a time zero from which to measure the body’s response. It’s done in the lab when you tie off a coronary artery. The first thing you see is you get edema formation because fluid comes out of the vasculature and leaks into the adjacent tissue. If you think teleologically(?) one of the first thing you want to do is dilute out the toxins by increasing blood flow to that area, opening the space between the endothelial cells and let water gush out to give you intercellular edema. You can see space between all the cells in the picture due to the edema. The second wave of activity is the recruitment of neutrophils (PMNs). When you think of acute inflammation think of PMNs. They are the firetrucks. They get in quick. After the PMNs, the macrophages start coming in and they take a little longer. They start in the blood vessel as monocytes, and because of increased blood flow and loosening of the junctions between the endothelial cells, the monocytes stick to the wall of the vessels and crawl into the tissue. By Day 2 and 3, the majority of the cells in the tissues are macrophages. Within the first day all the cells are PMNs.
5:How do neutrophils get there? We talked about the increased blood flow so there are more PMNs getting to the area. There’s a process called pavementing, and as you get sticking of the PMNs to the vessel you get complementary adhesion molecules on the PMN and endothelial cell binding to each other.
6:This is a diagram of that. During normal blood flow all the cellular components are in the center of the stream of blood. As you get increased blood flow you get turbulence and stasis. The cellular elements are near the edges and more likely to interact with selectins in the walls of the blood vessel, which are receptor molecules expressed by the endothelial cells. The integrins on the neutrophil interact with the selectins on the endothelial cell. You get rolling on the side of the blood vessel. After it has done that a while, you may get more than one ligand adhesion, and at that point you stop rolling and get a strong adhesion on the side of the vessel. It can then crawl between two endothelial cells and get into the tissue through diapedesis. So rolling, integrin-selectin interaction, emigration out into the extracellular space, and then the cells can do their thing.
This slide isn’t in the powerpoint online:Here’s an example of PMN rolling on an injured vessel in a pig. All the PMNs are stuck on the surface of the endothelial cells within an hour of the injury.
7:So what cause them to crawl into the tissue after sticking? That’s the process of emigration by chemotaxis or chemotactic mediators. Some classic ones are bacterial products, LPS. If you get a bacterial infection, you want to recruit PMNs to the site, so they are chemotactically attracted to LPS. Complement derivates such as C5a. C5a stimulates the inflammatory cascade. C5a recruits PMNs in to clean up the mess that is formed by a thrombus formation. Arachidonic acid derivatives, primarily leukotriene B4 is a chemotactic factor and also cytokines, with IL-8 being the more common/strongest chemotactic factor.
Why is chemotaxis important? (video on youtube) Here is a human neutrophil, and in the pipet is a chemotactic agent. Release of the agent causes the PMN to migrate toward the material. If you have damage to your tissues, the PMNs are very active and will travel toward the gradient of chemotactic material. That’s how you get all the cells to the tissue within just a few hours.
8:What happens if things aren’t working correctly? People with defects in the inflammatory system are helpful in studying the process. People with Chediak-Higashe Syndrome and even diabetes have low WBC counts. They don’t phagocytose as well and can’t kill microorganisms as robustly. People with a C5 deficiency are without the C5a chemotactic factor and cannot stimulate a high acute inflammatory response as effectively, so they get more severe chronic types of problems. Serum chemotaxis inhibitors, there are certain C5a inactivators, classic example is cirrhosis of the liver, sarcoidosis and other diseases (he doesn’t explain it further, but I’m guessing this would result in more chronic inflammatory problems). WBC locomotion inhibitors, people on Chloroquine or people on cancer chemotherapy. One of the modes of action of those drugs is to inhibit the locomotion of white blood cells.
9:So you have chemotaxis to get them where the problem is. What do they do once they are there? Either phagocytose the material or degranulate their lysosomes and release material that can break down the cause of the problem. There are three steps to phagocytosis. You must recognize the foreign material, attach to it, and engulf it to interact with internal enzymes.
10:Recognition is the first step. What’s the best way for an inflammatory cell to find the pathogen? Opsonization. The best example is when an immunoglobulin binds to a virus or Ag. The WBC might not recognize the virus as foreign, but recognizes the Fc region of the Ab, and knows to phagocytose the bound virus. Same thing with C3b, which will bind to a virus. A macrophage will recognize it and phagocytose the cell. Other examples are mannose binding proteins produced in the liver. It covers the virus or whatever and is recognize by a macrophage or PMN.
11:Here’s a diagram. You have a receptor on the macrophage or PMN that binds a compound on the surface of a virus. You have a virus with a mannose group on the surface, it binds to the mannose receptor on the macrophage. The macrophage invaginates its cell membrane and engulfs the virus into a phagosome. The virus is now inside the macrophage. Lysosomes, membrane bound bags of enzymes, will kill the organism. It comes over and fuses with the phagosome and becomes a phagolysosome. The enzymes then break down the microorganism.
12:What is the main mechanism for killing? By using oxygen free radicals that form hydrogen peroxide. Hydrogen peroxide reacts with chlorine, and you produce bleach, which is the best thing to kill microorganisms. So inside the phagolysosome you produce bleach to kill the virus. There are hydroxyl radicals that are powerful oxidizing agents also that can degrade the protein and kill the virus.
13:You have a myeloperoxidase which is the main enzyme that is used to combine the hydrogen peroxide with the halide, mainly chlorine, to produce HOCl (hypochlorous acid, bleach). You could also combine it with bromine and other halides. Hydrogen peroxide and ferrous ion without myeloperoxidase will generate OH (hydroxyl) free radical, a non-specific oxidizing agent.
14:PMNs will live a 1-3 days. Macrophages (monocytes when in the blood) hang around for a longer time. There are some chronic diseases caused by macrophages. There are also many chemical mediators in acute and chronic inflammation.
15:There are two classes. One are the preformed mediators, the ones that are formed and stored in the cell and can be released quickly when the cells are stimulated. These include histamines and serotonin, and lysosomal enzymes. They react quickly, in seconds to minutes. The secondary effects, that take minutes-days, are the factors that the body has to produce new when there is a stimulation. Some of the newly synthesized are leukotrienes, platelet activating factor, nitric oxide, activated oxygen species, cytokines, and prostaglandins. The other thing to remember about inflammation is a lot of the systemic mediators of inflammation and complement factors are all produced in the liver. An alcoholic with cirrhosis doesn’t have many liver cells left to produce all this stuff, so they cannot produce as large an inflammatory reaction to an infection. They are more susceptible to infections.
16:Every exam created by man has a picture of the arachidonic acid cascade and the production of thromboxane, prostacycline, PGG2. A large number of inflammation mediators are made through the arachidonic acid system. It’s very straight forward in terms of what you do to a sick person with a large inflammatory response. You give them steroids because they block the first step in the arachidonic acid reaction, so that will slow the production of the inflammatory mediators. If you have a headache you take aspirin which blocks cyclooxygenase which effects the prostaglandins that are causing you vasoconstriction and thus pain. It all starts with the arachidonic acids which are part of the cell membrane and then go through this process. There are the Leukotriene B4 which we said earlier was a powerful chemotactic agent, and other things. “I don’t know if you need to memorize everything on the chart, but be aware of some of the key features.”
17:What about non-inflammatory and inflammatory conditions that we see? Whenever you have altered blood flow, swelling, that’s fluid coming into the tissue from the blood, so that’s transudate, if it’s just the fluid. If you have an infection, then you get an inflammatory response and an exudate, which is fluid and cells and proteins and everything else coming out.
18:This is pulmonary edema, with acute inflammation of the lungs and altered blood flow through the lungs, so this a transudate.
19:Types of exudates. They are associated with an inflammatory reaction, due to injury or infection. A serous exudates, an example is a blister when you get burned. The fluid inside is a serous exudate. You will see fibrinous with uremic pericarditis and viral pneumonitis. Fibrin, which is a soluble protein in the blood, when it is stimulated from the clotting cascade forms an exudates. A purulent exudate is found in meningoccocal meningitis and is puss, which is full of PMNs and other inflammatory cells. Eosinophilic exudate is usually IgE mediated, an example is asthma, with it being around the bronchioles. Hemorrhagic exudate is with rickettsial infection, Rocky Mountain Spotted Fever,or the organism causes damage to your endothelial cells. It’s due to damage to the wall of the blood vessel. You get hemorrhaging and thus the name. A pseudomembranous exudate, we don’t see it too much more due to vaccines, is with diphtheria. Pseudomembranous entercolitis is the most common cause of diarrhea if you have had antibiotics.
20:Here’s an example of someone who burned his foot and there is a serous exudates. The clear white fluid that’s in the blisters is serum.
21:Here it is histologically. The surface of the kin is burned, and these are shrunken cells, and here is the hole from the blister.
22:This is an example of a fibrinous exudate, pericarditis. This is a patient with renal failure, and it tends to irritate the lining of your heart and pericardium. Irritation leads to the release of soluble fibrin being released into the fluid in the sac, and then the fibrin forms fibers and turns into a fibrinous exudate. This is the surface of the heart. The red area is the pericardium that has been cut and pulled away.
23:This is it histologically. Here is the wall of the pericardium made of fibrous connective tissue. This is the fibrin, it looks like a thrombus. There are a few inflammatory cells, and some proliferating mesothelial cells. The main red cells are fibrin.
24:Here’s an example of acute inflammation, a purulent exudate. The white material is puss (WBCs) between then brain and meninges.
25:Histologically you can see the puss between the brain surface and the meninges. (I think it’s the stuff on the right)
26-27:Here‘s a blood vessel that is distended. Out in the space you get all the inflammatory cells, and they are all PMN’s. This is an acute inflammation response with a purulent exudates from meningitis.
28:Here’s a trachea and bronchi of a patient with diphtheria. The surface of the tissue dies and forms a cast of the trachea.
29:Histology section. Here is the trachea and the inner surface of it is the diphtheritic membrane, the pseudomembrane. It’s a pseudomembranous exudate. It’s the layer of cells that were there, they have all died and are a coating of the inside of the trachea.
30:Here’s the wall of the trachea. It’s dead cells, fibrin, all stuck together to form a wall there.
31:We talked about pulmonary edema, which is just the excess fluid in the tissue. Ascites is when you get edema in the abdominal cavity. And we talked about pus as an accumulation of leukocytes, primarily PMNs.
32:When you get acute inflammation, you first see a vascular event. You get an increase in blood flow and release of fluid into the interstitial space. That’s followed by a recruitment of cells, PMNs and secondarily macrophages, that go into the infected tissue and try to fix everything through phagocytosis and binding to the toxins and eating the dead tissue. If they can do that, the tissue goes back to normal, and that’s called resolution. Resolution is clearance of the injurious stimuli, mediators and inflammatory cells, replacement of injured cells, and everything goes back to normal function. If you get a strong inflammatory signal, many cells come out and that will give you pus formation. That’s a purulent exudate in the tissue. If you get a purulent exudate and dead tissue you get an abscess. If you don’t get a resolution with acute inflammation, you get a chronic inflammation, and things don’t go exactly right you can get fibrosis or scar formation.