 Hello everyone, welcome back to another session in Dentistry and more. Today we have a small topic in microbiology that is types of hypersensitivity. So hypersensitivity which refers to undesirable reaction which is produced by the normal immune system which includes allergies and auto-immunity. So auto-immunity is nothing but the our own antibodies is fail to recognize the antigen that is antigen is something which comes from outside. It fails to recognize the antigen and it acting against our own cells which are the cells which these antibodies are supposed to protect. So those are the auto-immunity reactions and these reactions may be damaging uncomfortable or maybe occasionally it could be very fatal. Now let's see the types and the details of hypersensitivity. So hypersensitivity we have four classification. Type one is immediate type or anaphylactic or atopic. Type two is antibody dependent. Type three is immune complex. Type four is self-mediated or delayed type of hypersensitivity. Now we will begin with the type one. So type one hypersensitivity is also known as immediate or anaphylactic hypersensitivity. So the reaction may involve skin, attic area and eczema. So conjunctivitis can be seen in eyes, rhinitis, rhinorrhea in nasopharynx and it can also lead to bronchopulmonary tissues that like asthma reactions and gastroentritis in gastrointestinal tract. So these are the immediate reaction. So all are immediate outcome of this antigen attack and this hypersensitivity. So the reaction may cause a range of symptoms from minor inconvenience to death. So maybe the reaction usually takes 15 to 30 minutes from the time of exposure to the antigen and it can have delayed onset of 10 to 12 hours. So this is our cell. So the foreign particle is known as antigen and we have antibody inside. So this is supposed to be protective against the antigen. And we have our own cell, normal cell. So sometimes the antibody act against our own cell that is known as autoimmune reaction. These antibodies are supposed to protect ourselves but sometimes it fails to recognize the antigen and our own cell and it act against our own cell that is known as autoimmune reactions. Anyway, so the immediate type is usually mediated by IgE antibody to those specific antigens. So the primary cellular component in this hypersensitivity is the mast cell and basophil and the reaction is amplified or modified by platelets, neutrophils and esophils. So mast cells, they get stimulated and relays his stamens. So that is type 1 reaction. So in type 1 the example is atopic reactions which is type of localized NFL axis. In these patients there will be higher levels of IgE antibodies. Now let us move on to type 2 hypersensitivity which is also known as cytotoxic hypersensitivity and may affect a variety of organs and tissues. So the antigens are normally endogenous although exogenous chemicals which can attach to cell membrane and also lead to type 2 hypersensitivity. Endogenous means within the cell not coming from outside. So the most common one is drug induced hemolytic anemia, granulocyte and thrombocytopenia and also penciline allergy also belong to type 2 reaction. So the reaction time is minute to hours and is primarily mediated by the antibodies IgG and IgM and also the complement system. So phagocytes may also play a role in type 2 reaction. So these lesions contains antibody, complement and neutrophils in general. So the hemolytic thrombocytopenia we know when there is RH positive baby born to a RH negative mother for first time. So there will be antibody acting against the baby. So that is coming under type 2 hypersensitivity reaction. Now let us move on to the type 3 which is antigen antibody immune complexes which is IgG mediated and there will be large amount of antigen and antibodies form complexes in blood. So if it is not eliminated which can be deposited in capillaries or joints and trigger inflammation. So the reaction may be general such as serum sickness or may be or may be involve individual organs including skin such as systemic lupus erythematosus or arthus reaction, kidney such as lupus nephritis or aspergillosis in lungs and rheumatoid arthritis in joints. So that is particularly for one organ and if it is very general that will be serum sickness. The rest all are affecting one particular organ and the reaction may be pathogenic mechanism of disease caused by many microorganisms. So it takes 3 to 10 hours after the exposure to antigen and it is mediated by soluble immune complexes. So they are mostly IgG class although IgM also be involved. So the antigen may be exogenous such as bacterial viral or parasitic infections or it could be endogenous. And the type 4 is delayed type which the reaction involves by the sensitized T cells. There is no antibody involved and the sensitized T cells and there is release of lymphokines as mediators and amplifiers. So they are mediated by cells rather than antibodies that is a peculiarity of type 4. So mostly the contact dermatitis transplant rejection granuloma all are belong to type 4 category. So that response usually comes after 48 to 72 hours. So there will be continued macrophage activation which can cause chronic inflammation which results in tissue lesions, scarring and also granular formation. So that is about the 4 types of hypersensitivity. So let's summarize the points of all 4 categories. So first let's see about the antibody which is involved. So type 1 IgE, type 2 IgG and IgM, type 3 also IgG and also IgM is there but on very little amount. So IgG and IgM but very little amount. As type 4 is basically T cell mediated and there is no antibody involved. And type of antigen in type 1 it is exogenous, type 2 is cell surface, type 3 soluble antigen and type 4 is tissues and organs. The response time for type 1 it is 15 to 30 minutes, type 2 minutes to hours, type 3 it could be 3 to 10 hours. Type 4 is very delayed that is after 2 to 3 days that is 48 to 72 hours. So most common appearances are the type 1 is wheel and flare that is wheel and flare, type 2 is lysis and necrosis, lysis and necrosis in type 2. In type 3 erythema, erythema and necrosis, erythema, erythema and necrosis whereas type 4 which is erythema and inturation. Inturation we can see in tuberculin test we expect a result after 48 hours. If inturation is present we confirm it as tuberculin positive or tuberculosis. So that is about the appearance and now the histological part. So type 1 we have basophils and isnow fill, type 2 we have antibody and complement. This is macrophages and complement neutrophils, type 4 we have lymphokines, monocytes, lymphocytes. So the cell involved that is the antibody or the T cell. So 1, 2, 3 are basically antibody involved whereas type 4 is T cell. And the examples for all 4, the type 1 is allergic asthma, heffy, type 2 is erythroblastosis, fetalis and thrombocytopenia, penicillin, allergy. Type 3 is systemic lupus, erythematos, serum sickness, atlas reaction. Type 4 is tuberculin test, granuloma.