General Pathology- Immunopathology I Pg. 8

General Pathology Transcriber: Clay McEntire 9/24/08 58:04 (Length of lecture) Immunopathology I- Dr. Bucy

1. This lecture is 2 parts-- Classical information: including the 4 types of hypersensitivity, and Diseases where antigen (Ag) involved is not a self Ag. And on Thursday we’ll talk about autoimmune diseases, which is characterized by Ag’s derived from the host.

2. The four types of hypersensitivity is a classical thing to learn. These 4 classes will be great to know for board exams. This scheme was developed in the late 1950’s when there was no differentiation between T and B cells. At this time, the skin test was the main source of information. With this, you put Ag in the dermis of someone. Reactions take place at different rates depending on with type of hypersensitivity is being triggered. The time of reaction was then used to categorize the dypersensitivities.

. Type 1 is immediate (10 minutes). It’s IgE mediated.

. Type 2 isn’t mentioned with the skin test time tables because in the 1950’s they already had a different model test: blood- antiserum agglutination.

. Type 3 peaks in 8-10 hour time frame. Involves immune complexes.

. Type 4 is the reaction that will take place 24-48 hours later. They are non- Antibody mediated. Instead are cell mediated responses. Primarily are mediated by CD4 T cells that activate macrophages and other myeloid lineated cells to cause tissue injury.

3. Type I: This type is also the “anaphylactic type” because “anaphylaxis” is any kind of systemic response. This is immediate hypersensitivity, and IgE is the main player. The mechanism is that you have antibodies to allergens, and the IgE is bound by Fc receptor epsilon on the surface of cells. In the serum there is actually very little free IgE floating around. When IgE molecules encounter Ag, they crosslink to that Ag, and the cell (maybe a mast cell) releases its mediators and those mediators are responsible for the allergic response that occurs. Mediators cause the hypersensitivity. Systemic anaphylaxis involves an Ag that is distributed all over your body (different from hay fever which is local). This is seen with penicillin allergies because you have penicillin triggering mast cells all over the body at the same time.

4. This is the cellular pathway described previously. Somehow you have to get IgE that are specific for allergens produced. This process is similar to other Ig production—you have a CD4 helper T cell interacting with a B cell that will differentiate into a plasma cell, which makes the actual proteins. Plasma cells sit primarily in the bone marrow. IgE leaves and attaches to mast cells, for instance, via the Fc receptor. These cells sit around small vessels, and if Ag crawls out of the vessel the Abs crosslink to the Ag leading the cell bound to the Fc portion of the IgE molecules to release its chemical mediators. What are the mediators and what do they do?

Histamine is one of the primary mediators. When you take antihistamines, it blocks the action of this mediator. It doesn’t do anything to block the action of IgE. It simply masks the activity at the end stage of the process. General Pathology- Immunopathology I pg. 2 Clay McEntire 5. Initial signals are brought about by Ag crosslinking with 2 different Ab molecules (at least). The IgE molecule signals the cell via the Fc receptor, and the result is degranulation. Most of the chemicals within the cell are already formed. We know what most of them are, but he said it’s safe to say that there is more to be discovered. Histamine is a primary character, and arachidonic acid metabolites (leukotrienes) are the secondary characters resulting from degranulation. As you know drugs like aspirin block this transmission (I think he was talking about the arachidonic acid reactions), but anti-histamines block further down at the receptor level on the target cells.

6. Type I hypersensitivity occurs within seconds. The middle picture shows granulated cells congregating around a vessel. The picture on the right shows some eosinophils, which also have Fc receptors for IgE. Someone who has hay fever will have eosinophils congregated in the nose. This type of allergic response can also occur in the eye; therefore there is a need to make ocular medications to be hypoallergenic because you don’t want something that you’re going to put in your eye to lead to an allergic response. A chief test for this is to use a rabbit’s eye. Cosmetic companies run these tests on their makeup. If it causes inflammation, which is the type 1 hypersensitivity, then they need to reformulate their product.

7. This is a dust mite with its feces surrounding it. The feces has a protein that commonly stimulates IgE. Cockroaches also express the same protein. A lot of children have asthma because they are exposed to dust mite feces—they are simply allergic to dust. The only treatment that really works to prevent an asthma attack is to keep away from the Ag. Tobacco smoke and air pollution may exacerbate asthma symptoms too.

What is the normal function of IgE? They have a specific role against large parasites (not bacteria or viruses). Now a clean water supply is pretty much all we need to avoid parasitic infections. So we don’t really need this defense mechanism anymore. Some biotech. companies are trying to find a way to just amputate this whole process to avoid the allergies that it brings with it.

8. Type II hypersensitivity is also called antibody-mediated cytotoxic hypersensitivity. There are 2 basic processes that come into play. The first is Abs and complement which will mediate the death of a cell that has Ab bound to it, and the second is ADCC (antibody dependent cell cytotoxicity). In ADCC, cells will recognize and kill target cells cells that have Ab bound to them via the Fab region. The killing cells will bind the exposed Fc region of the Ab. These Ab molecules are IgG. An example of this would be transfusion reactions (erythroblastosis fetalis and the key one- autoimmune hemolytic anemia). Type II was originally defined by hemolytic anemia tests (as was mentioned before).

9. Top picture: This shows complement activation. The key point with complement is that it doesn’t involve a cell. It’s a series of proteins that are soluble in the plasma. When combined with proteins they provide a complex that leads to a hole formed in the plasma membrane. This hole leads to Na+ leaking out, K+ leaking in and cell dies. This is an example of necrosis as opposed to apoptosis. General Pathology- Immunopathology I pg. 3 Clay McEntire Middle picture: Fc receptors are present on cells that recognize Ab-Ag complex. Complement proteins also recognize the complex. C5a and C3a are produced, and they are chemotactic factors for neutrophils, which take place in the process.

Bottom picture: Antibody-mediated cellular dysfunction is sort of a separate class. Some classifications will lump this in with type II, and some will list it as a class V reaction. With this process, the Ab sprues up a function, but it’s not by killing the cell itself. It’s by “punching the cell itself in the eyeball of a receptor that’s very critical.” For example, in the thyroid epithelium, the TSH receptor is the molecule that really controls how much thyroid hormone you make. If you get an Ab that stimulates that receptor, you may make too much thyroid hormone. The thyroid increases in size and you now have Grave’s Disease, which will be mentioned on Thursday. Another example of this type of reaction is seen with Myasthenia Gravis. With this disease, an Ab has been produced to bind the Ach receptor at the neuromuscular junction. This inhibits the transmission of the activation signal to the muscle therefore inhibiting a response.

10. An example of a type II hypersensitivity is erythroblastosis fetalis. This occurs when a father who’s Rh+ and a mother who’s Rh- have a child that’s Rh+. During birth, there is some bleeding, and the mother forms an antibody (IgG) to the Rh+ factor. That bleeding is also how HIV is transmitted from mother to child—not through the placenta, but because of blood exchange during the birthing process. In a following pregnancy, the IgG Ab could then cross the placenta and bind the red blood cells of the fetus if the second baby is Rh+, killing the fetus.

There is a treatment that prevents these complications. You simply give an antibody to this Rh factor right at delivery. That Ab clears the Ag, and the mother never becomes sensitized. “Rogam” is the term used for the Ab treatment.

11. Here’s a long list of other diseases with regards to type II hypersensitivity. **Watch for a matching question to come from this in the future. It’d be a good idea to take a look at this list some time before the test. He said it’d be perfect for a matching question!

12. Type III is the Immune Complex mediated process. The key point here is that the immune complexes are soluble aggregates of some Ab that’s binding to an Ag. The Ab can bind 2 Ag, but the Ag has many epitopes that can be bound, so you can get macromolecular complexes circulating through the plasma. Those complexes will deposit in particular places, primarily in cells that have Fc receptors (like small vessels and messangial cells in the kidney), leading to disease. Aggregated immunoglobulin in the immune system signals nonspecific cells to attack. (ie if there is a bacterial invasion, they’ll have Ig aggregates on the cell surface, so the immune system is geared up to protect against such complexes.) Endothelial cells of vessel walls, and glomeruli are the target cells of this immune complex deposition. Sometimes the complexes get pretty big and can clog up the glomeruli, since the kidney is the filter for the blood. This incites glomerulonephritis. The skin test is called the Arthus reaction. This works because Abs form around a localized Ag deposition, and you activate an immune response that doesn’t involve Tcells. The intensity of an immune complex disease depends on how large the complexes are and if they are charged or not. For instance, DNA can lead to rough immune complex disease General Pathology- Immunopathology I pg. 4 Clay McEntire because it is a pretty large and highly charged molecule. Other common antigens that lead to immune complex disease are hepatitis virions.

So the Ab-Ag complex doesn’t have anything to do with the specificity of the Ab, like with type II. Remember with type II, the target cells that are injured have the Ag on their surface, and the Ab seeks those cells out, causing damage. With type III, it can be “any ole antigen;” it’s how big and sticky the complex formed is that is important.

13. The mechanism to cause injury occurs because these complexes attract neutrophils and activates complement. The neutrophils degranulate, and enzymes of the granules digest proteins and lipids, causing a persistent problem. One can suspect that a disease like periodontitis, which is a chronic disease in the root area of the tooth, involves this mechanism. There are bugs around the roots, and you get Abs to them. The therapy needed for these patients is to scrape away the complexes. The bottom line with this disease is that you have Ag from the bacteria, your body makes Ab to that Ag, and you get inflammation and tissue destruction.

14. The kidney is another place. The site of complex deposition is important here in determining what kind of glomerular nephritis occurs. Three sites of deposition are:

a. Endothelial cells. Larger complexes are caught here because they can’t pass through.

b. In the basement membrane

c. Epithelial side (opposite side of the basement membrane). Smaller complexes make it to this side.

15. Arthus reaction: artificially put the Ag into the skin, activating neutrophils and complement which do their business on whatever site this is. You’ll also get platelet aggregation/ thrombosis, and infarction in small vessels.

16. If you look at it grossly, this is a person’s arm where antigen was placed. The site is raised, red, and tender. This occurs in about 10 hours. If the swelling gets to be a certain size, then you can say that the person has antibodies formed for that antigen, allowing you to conclude that there has been previous exposure to the Ag.

If someone shows you a similar type of reaction, it could be a DTH (delayed type hypersensitivity), but this reaction would peak at 24 or 48 hours.

17. If you’re given a histologic shot of the lesion… Is this type III or type IV? What can you see here that helps you tell the difference? Neutrophils is the answer. They are present in the arthus reaction. In the slide, you can see a lot of PMN’s/ neutrophils. Type IV would have a lot of lymphocytes and macrophages. That would be acute inflammation (type III) as opposed to chronic inflammation (delayed type- type IV). General Pathology- Immunopathology I pg. 5 Clay McEntire 18. Lupus focuses on nuclear antigens- DNA. You get a lot of different constellations of symptoms. Poststreptococcal glomerulonephritis occurs in the glomerulus membrane where Ag-Ab complexes imbed. Polyarteritis nodosa is a vasculitis that occurs. A common Ag (but not the only one) is hepatitis B virus. And a final quick point is called serum sickness. This occurs when you inject a foreign protein (an antibody). An example is if you get tetanus—You can inject horse antibody that binds to the toxin and neutralizes it. The problem is that your own immune system will react to those antibodies, and you can get serum sickness, which is a systemic vasculitis (blood vessels) and glomerulonephritis (glomeruli in kidney). Once the Ag is cleared, the pathology goes away.

19. Type IV is the cell mediated type of hypersensitivity. This one is more complex as far as the mechanisms go because it’s kind of the grab bag category. The key thing going on here is CD4 T cells that secrete cytokines (gamma interferon and tumor necrosis factor alpha are primary players), which activate macrophages leading to an influx of mononuclear cells into that site.

Another form is granulomatous inflammation which basically is a process in which the macrophages have an antigen that they can’t really digest. For example, TB has a waxy coat and it’s hard for the macrophages to digest it. Fungal cell walls, and other materials like berrylium are other substances that macrophages have trouble with. The presence of the macrophages and the lymphocytes that they attract allow this reaction to be histologically distinct from type III.

CD8 T cells/ Cytotoxic lymphocytes can also mediate tissue injury. NK cell activity can occur directly with recognition or the NK cell can mediate ADCC with the class II pathway.

There are a lot of different ways to measure antibodies via binding assays. Measuring cell mediated immunity is a very complicated process. Essentially there isn’t a good way to do it. Therefore we must still result to the skin tests (like with TB skin test).

20. Classic delayed type is seen in the above picture. This involves activation of endothelial cells and macrophages. Cell mediated cytolysis follows in a one-to-one killing of an infected cell.

21. This picture shows tuberculin-type hypersensitivity. Ag is introduced, and becomes presented on an APC. A stray wondering T cell with a TCR specific to the Ag comes across the APC, and they jump into action—secrete a bunch of cytokines which recruit other cells. A lesion results.

22. This is a picture of Dr. Bucy’s arm. A long time ago, he did an autopsy on a lady who had systemic tuberculosis. Later he got a TB skin test, and it showed up positive. If that happens, you have to take a drug that blocks the growth of the mycobacteria. This drugs grows very slowly, so you have to take the drug for an extended period.

23. This is a stain for CD4. It’s been stained with H & E. It’s showing that there are a lot of T cells here. Not neutrophils which would indicate a type III mechanism.

24. This is a mouses ear, and this foaming thing is the cartilage in the ear. Ag is injected into the ear pinna. If the ear thickens as a result of edema—that’s a positive response. With delayed type, General Pathology- Immunopathology I pg. 6 Clay McEntire you get macrophages and T cells at the site of the infection. In immune complex disease, the antigen is in circulation and you’ll get a systemic type of pathology. Immediate hypersensitivity is also at the sight of infection (ie if you breathe in the Ag, you get rhinitis; if it’s injected in the skin, you get a skin lesion).

25. This is a picture of granulomatous inflammation associated with chronic T cell and macrophage inflammation, primarily because the Ag just won’t go away. There are certain things that go along with that.

26. This is a diagram that shows what the CD4 and CD8 T cells do. He didn’t go over the diagram though.

27. These are examples of what we think are T cell mediated or type IV responses. He listed some: diabetes, multiple sclerosis, rheumatoid arthritis, inflammatory bowel disease, contact dermatitis… (He said he’d talk more about contact dermatitis on Thursday)

28. Now we’re going to switch gears. The rest of the lecture goes into some reactions that aren’t classified by the mechanism of reaction, but are classified by the Ag itself. There are two forms of leprosy, but there is only one bug. The difference is how the host responds to that bug. In the disease called Tuberculoid leprosy, you have a strong immune response which kills most of the organisms, but the damage is a collateral injury to tissue wherever the bugs were living. They like to live in peripheral nerve sheaths, and this damages the peripheral nerves and that causes big problems.

Lepromatous leprosy is characterized by the host’s immune system recognizing that the immune response occurring is actually worse than the disease itself. It then suppresses the specific immune response, a delayed type hypersensitivity, and the organisms grow. Big bulbous lesions will form. This is the form you read about in the Bible. It’s very infectious because the skin lesions have a lot of the viable organisms living in them. If you touch any of these lesions, you’re very likely to catch the disease.

29. This is a picture of tuberculoid leprosy. You can see a lot of lymphocytes present. This is a peripheral nerve sheath that’s being destroyed by the immune response.

30. This is a picture of lepromatus leprosy. The big foamy cells are macrophages that are filled with the organisms. The red stain is specific for the mycobacterial organism. The organism load is high, and that’s what’s causing damage to the tissue, not the host’s immune response.

32. Streptococcal disease is another disease that is the result of an infection that kicks off an auto immune response. One possibility is that you get glomerulonephritis immediately after infection because you get Abs produced in response to the Ag. The complexes deposit in the kidney like with a typical type III response, resulting in glomerulonephritis. Rheumatic fever is another option too. It results because the Abs produced to the pathogen cross reacts with a self antigen on heart cells, causing tissue injury. Also, if someone has a sore throat, it’s good to rule out Beta General Pathology- Immunopathology I pg. 7 Clay McEntire hemolytic strep as soon as possible because other consequences could follow (ie the other symptoms associated with streptococcal disease).

33. Contact dermatitis is another situation of a lesion that is brought on by an external antigen. If you expose it to the skin, a lesion follows involving “these two bulla formation or blisters.” Intracellular edema/ epidermal spongiosis also follows. This process involves a high reactivity to certain proteins. Poison ivy is a common example of that process.

34. This is another example of contact dermatitis—benzoine toxicity. This person got it on their lips after getting the agent on her finger.

35. These are called bulla (same as “blisters”). They can vary in size. The skin cells also have edema which leads to swelling. That’s why the skin looks crusty or weepy—it’s leaking fluid.

36. This is poison ivy. You can see exactly where the sensitizing agent hit the skin.

37. Penicillin allergy is very common because it’s highly reactive as an allergen. It works as an antibiotic by covalently binding to a particular molecule in bacterial cell walls, hindering bacterial cell division. That same chemical reactivity can react to proteins, and some people get an immune response to that conjugate. You can get an IgE or IgG response, and the conjugation can occur on different kinds of cells. If you get intravenous penicillin, the Abs may bind to RBCs leading to a hemolytic anemia. If you take it orally, you may have some GI problems and so forth.

38. Tumor cell antigens are another target for immune responses that are a little bit different. They are not quite cell antigens, but it’s a foreign antigen. There’s been a lot of hope without much success in analyzing this growth to find a way to hinder tumor growth with cancer. The key element to get the inhibition going would be to find an Ag that’s in the tumor but not in the host, and it hasn’t been very easy to find one. One that does work is if the tumor was initiated by a virus (like papilloma virus), you can get an immune response to that virus, which would block tumor growth because the tumor itself is dependent on the virus. There is a drug GARDISIL that is given to adolescent girls to prevent infection from papilloma virus, possibly preventing cervical cancer down the road.

39. The final source of antigen is tissue based. If you get a tissue/ organ transplant, you’re getting foreign antigens, and an immune response will follow.

40. There’s a special thing about alloantigens-- there are Donor APC’s (which stimulate T cells). The MHC molecules will be different and T cells recognizes this difference. You will get an especially vigorous immune response because of this.

41. Most of the injury to transplant involves the type IV pathway. This is a picture of how all that works. This is where he realized he was running out of time, but I think before he left this slide he just said that you can get damage to renal tubules and blood vessels after a transplant. General Pathology- Immunopathology I pg. 8 Clay McEntire 42. Mechanisms of transplant rejections: The classical ones are based on how fast it happens (He just read the names of the bullet points, but I guess that the list increases in amount of time that it takes for rejection to occur. For instance chronic rejection takes a long time). You have to realize that evolution didn’t expect us to be sharing organs.

43. There isn’t any real mechanism for transplant rejection. Actually anything that causes injury is transplant rejection. All kinds of different things can do that.

In more modern terms this list would be longer, but the two big ones are the first two: cytotoxic damage and the “DTH” mechanism with CD4 T cells and macrophages. You can also get chronic injury to vessel walls. Most people with heart transplants who die, die from vascular injury—not actually from acute rejection of the organ.

Drugs given to help resist tissue rejection work to block the T cell-Ag interation by interrupting the signal transduction of the Ag receptor and the genes that are activated when the Ag receptor is stimulated through a molecule called calcineurin. Cyclosporine A and glucocorticoids are examples of that kind of drug. These will work to cool off macrophages.

You can also get chronic injury to vessel walls. Actually most people with heart transplants die of heart attack due to vascular breakdown of vessels supplying the heart. It’s actually not a problem of acute rejection, it’s actually more of a long term vascular injury. We’re not really sure what actually causes this.

45. The clinical monitoring of different kinds of grafts is different for each case. For the kidney and liver, you can monitor things in the blood. The heart is not so easy—you have to do blind biopsies. If you wait for a drop in blood pressure, then the rejection is already underway. Bilirubin (for the liver) and creatinine (for the kidney) build up if there’s a rejection of these organs and that’s easier to monitor. There’s nothing to monitor for the pancreas.

46. Key points of solid organ transplantation. He skimmed this slide not really going into any of these points.

47. Summary slide. Type I- IgE. Type II- IgG Abs that kill other cells. Type III- immune complex . Type IV- T cells.