in a previous video on this channel i've talked about the complement system with its three pathways the classical pathway the alternative pathway and the lectin pathway today we have an introduction about the types of hypersensitivity reactions we have type 1 type 2 type 3 and guess what type 4 hypersensitivity and this classification is based on what medical says it's based on the time mainly type 1 is the fastest type 4 is the most delayed with that said now let's get started hi person 7 type 1 type 2 type 3 type 4 type 1 immediate but type 4 is delayed okay about type 2 cy2 toxic look at this type 2 is psi 2 toxic and type 3 you have 3 antibodies what do you mean by 3 i mean the antibodies are floating in the plasma they are floating in your blood they are not bound to cells they are not situ like type one also you can describe type three by three words serum immune complexes hypersensitivity which one is the fastest type one which one is the slowest type four can you describe type 1 in few words sure immediate anaphylactic ige mast cells they rupture pew they degranulate pu releasing histamine and histamine can give you the symptoms of an anaphylactic shock how about type 2 cy2 toxic what do you mean i mean i have antibodies okay these antibodies are bound to antigens okay and this happens on the surface of the cell the cell is the cy2 that's why type 2 is cy2 toxic okay how about type 3 3 is free you have antigens and antibody complexes same as 2 yeah but with one difference the big difference is this happens in the blood and after this since they are hanging around in the blood the antigen antibody complex can end up being deposited in the blood causing vasculitis in your joints causing arthritis in your kidney causing nephritis etc etc etc in type 1 type 2 type 3 we talked about antibodies like ige like the antibody that is cytotoxic like the antibody that's freely floating in the blood but type 4 has nothing to do with antibodies type 4 has nothing to do with the hemorral immune system type 4 is about t lymphocytes cell mediated immunity no antibodies heck no the t lymphocytes are super sophisticated they communicate with each other via cytokines which include the interleukins which is the internet of the leukocytes this is also the story of making a granuloma and this takes time here is a quick overview of the four types of hypersensitivity type one immediate okay within a minute all right hey moral immunity which means i'll say antibodies yes such as ige immediate immortal pre-formed antibodies remember ige is eew what do you mean by evil allergy anaphylaxis had to be asthma using ew beasting ew how about type 2 type 2 is cy2 toxic okay we have an antigen antibody complex were on the surface of the cell and these antibodies could inhibit the target most of the time or they could stimulate the target in one case only that's why some crazy textbooks define this specific type as type 5 hypersensitivity but this is a very bizarre classification that only lasted for five minutes and then they went back to classifying hypersensitivity as four types can they inhibit the target sure they can cause inflammation and cell dysfunction inflammation is seen in anti-glomerular basement membrane antibody disease also known as good pasture syndrome rheumatic fever hyper acute transplant rejection this is how your body rejects organs or they can cause cell dysfunction such as myasthenia gravis and pemphigus vulgaris my muscles are in trouble my skin is toast they stimulate the target organ only in one case which is the case of grave disease i have antibodies against the receptor okay what kind of receptor this is the receptor waiting for the tsh so it's called the csh receptor okay but these antibodies will come and stimulate the target have you ever heard of antibodies that stimulate the target no antibodies are weapons of destruction now this is an exception these are antibodies that stimulate the target leading to what well it says if tsh is binding to its receptor oh so a similar effect yeah what does tsh do it tells the thyroid gland to secrete tons of thyroid hormone so graves disease in a sense is a type 2 hypersensitivity reaction okay how about type 3 type 3 is also antigen antibody complex in a different location floating freely in the plasma okay this is the cause of serum sickness which is a diffuse and acute reaction or the arthas reaction it's not diffuse it's very localized in one spot on your skin and it's not that acute orthos is sub-acute serum sickness is generalized arthas is localized serum sickness is acute arthas is subacute and subcutaneous love it subcutaneous type 3 is also the tragic story of the nasty immune mediated vasculitis when these antigen antibody get deposited into the wall of the vessel this is vasculitis they can also get stuck into your kidney this is called immune complex mediated nephritis or into your joints immune complex arthritis this is what happens in lupus this is what happens in rheumatoid arthritis and jazillion other diseases about type 4 type 4 is the most delayed 3 days or about 72 hours or slightly less slightly more this is cell mediated i'm not gonna send antibodies to destroy no i myself i'm gonna go and kill that bacteria face to face i'm gonna have a strong word with this tuberculosis face to face cell to cell cell mediated or cellular immunity if i can kill the stupid invader i will destroy it how will he destroy it well we are t lymphocytes we have t cytotoxic cells we kill okay but if i can't kill it well at least i can surround it in a granuloma this granuloma can have caseous necrosis such as the caseiatin granuloma of tuberculosis histoplasmosis blastomycosis coccidioidemicosis or it could be done casey eating basically any other granuloma is going to be non-caseating a famous example is sarcoidosis how to make a granuloma is a story that we'll talk about soon but basically cd4 t lymphocytes will secrete interferon gamma which will stimulate the macrophages to make the granuloma brace yourself for the next video because we will discuss type 1 hypersensitivity reaction the story of the asthma the ad to be the bee sting first exposure second exposure early response versus late response and much more if you like this video you will adore my renal physiology course available at medicosisperfixnet.com comes with 10 videos 10 cases with notes of course i also have an endocrine pharmacology course learn everything you need to know about insulin the different types of insulin how to calculate the dose of insulin and much more and for a limited time get a 60 discount towards everything on my website just by using promo code new year learning at checkout thank you for watching please subscribe hit the bell and click on the join button you can support me here or here go to my website to download my courses be safe stay happy study hard this is mitochosis perfect scenarios where medicine makes perfect sense