this is the lecture for chapter 19 disorders of the immune system part 2 from the previous lecture I told you that the disorders of the immune system are divided into two basic types the first one is an overreaction or a hypersensitivity the second one is an under reaction or a loss of immunity for the hypersensitivities last time I talked about those specifically allergy and allergy is when your body has an immune response to a foreign molecule that is non pathogenic and because it's non-pathogenic and not dangerous this is an overreaction and the allergy is divided into four types type 1 which is anaphylaxis type 2 which is cytotoxic type 3 which is immune complex and type 4 which is cell mediated so those are the basic four types of hypersensitivity when you're talking mainly about allergy and the first three have to do with antibodies and the last one has to do with the t-cells in this lecture I'm going to focus on a different type of hypersensitivity and that is autoimmunity autoimmunity is where your immune system is responding to a self antigen so a self antigen is a molecule that is a normal part of your body and your immune system is responding to it so autoimmunity this is a disorder of the immune system because your immune system should be tolerant to all of your self molecules so when a person develops an autoimmune disorder they are experiencing a loss of self tolerance the exact cause of autoimmune disorders is not known but one hypothesis on how they can be triggered to develop is called molecular mimicry and the idea behind molecular mimicry is that an individual becomes infected with a microbe then that individual mounts an immune response to that microbe so either produce teen CTLs and/or antibodies against a particular antigen on that microbe but then what happens is that that antigen is very similar in shape and structure to a normal self molecule so the antigen that is found on the microbe is very similar in shape to a self molecule so that when the infection is cleared once all of these antibodies and CTLs have cleared the microbe from the body then those remaining antibodies now start binding to the self molecules that are similar in shape to that antigen so it's basically a cross reaction so the idea behind molecular mimicry is that the microbe has antigens on it that are similar to self antigens and when the infection is gone those immune components that recognize the foreign antigen will now recognize the self antigen so that is the hypothesis that they are using right now investigating right now that can trigger an autoimmune disorder there are some predisposing factors to developing an autoimmune disorder the main one is being female so something about a female's immune system makes women much more likely to develop an autoimmune disorder and there there is also a genetic component autoimmune disorders tend to run in families there are many different types of autoimmune diseases and they can be loosely classified into several different groups the first type of autoimmune disease I want to talk about are cytotoxic autoimmune disease cytotoxic implies that it's killing cells but for these types of autoimmune disorders the cells are not killed but their function is altered myasthenia gravis is a type of cytotoxic autoimmune disease and in myasthenia gravis there are antibodies which block the stimulation of muscle cells and so that results in a type of paralysis under a normal situation you have the neuromuscular Junction so here is the neuron here is a muscle cell and you know that the neuron will release acetylcholine to bind to receptors on the muscle cell and stimulate a contraction in myasthenia gravis there are antibodies that bind to the acetylcholine receptors and prevent the acetylcholine from stimulating the muscle cell so that inhibits contraction of the muscles and leads to paralysis so in this case the antibodies are preventing the muscle cell from contracting but they're not killing the muscle cell they're not killing the neuron they're just preventing the muscle cell from contracting Graves disease is another example of a cytotoxic autoimmune disease and in this case the antibodies are stimulating cells to over produce thyroid hormones so this occurs in the thyroid and the antibodies bind to the receptors on the thyroid cells over stimulating the cells so that they produce excess hot thyroid hormones so Graves disease is a type of hyperthyroidism and again the antibodies are not killing the cells they're just over stimulating the cells to produce more hormone than they normally should some symptoms of Graves disease are bulging eyes so you can see that and some of the individuals who have it and also if it's untreated Graves disease you would see it a goiter so where the thyroid would swell another type of autoimmune disorder our immune complex autoimmune diseases immune complex autoimmune disorders occur when antibodies bind to soluble antigen so the antibodies will bind to the soluble antigen and one of the results of antibody binding to antigen is agglutination which forms these complexes of antibody and antigen and these complexes are big enough to get stuck in basement membranes or in capillaries where they can damage the tissues damaged the capillaries and lead to inflammation lupus is an example of an autoimmune disorder and in individuals who have lupus they are producing antibodies against nuclear proteins so those antibodies circulate throughout the circulatory system and they bind to various nuclear proteins and forming those complexes which can get cut in the skin causing rashes they can get caught in the brain altering the function of the brain get cut caught in the lungs causing inflammation also causing inflammation in the spleen they can get in the joints causing arthritis and again in the kidneys damaging the kidneys and kidney damage is a hallmark of untreated lupus one of the classic signs of lupus is the butterfly rash so that's a rash that goes across the nose over the cheeks and form sort of a butterfly shape and that is caused by those immune complexes those antibody antigen complexes getting lodged in the capillaries in the another immune complex autoimmune disorder is rheumatoid arthritis and this is where antibodies are produced that recognize molecules in the joints so those immune complexes are formed in the joints where they cause a chronic inflammation in the joints which leads to damage in the joints and this is an autoimmune disorder so children can develop this there is juvenile rheumatoid arthritis it has nothing to do with overuse of joints it's an autoimmune disorder the last general group of autoimmune disorders are cell mediated autoimmune diseases and this involves the t-cells damaging tissues in the person's body type 1 diabetes is an example of a cell mediated immune disorder and for this type of condition this affects the pancreas the pancreas of course is the organ that produces insulin and this is what a normal islet would look like with the normal beta cells that are producing insulin in type 1 diabetes CTLs are activated against the beta cells and they destroy the beta cells in the islets which reduces the production of insulin so sometimes this is also known as insulin dependent diabetes because we have to artificially provide the insulin since the beta cells are being actively killed off by CTLs another example of a cell mediated autoimmune disorder is multiple sclerosis in multiple sclerosis you have antibodies and CTLs that are attacking the myelin sheath along the axons of nerve neurons and this destroys the myelin myelin sheath which leads to an inhibition of nerve impulses to the brain which results in a loss of control of the muscle of the body