Hypersensitivity Rxn Flashcards
hypersensitivity rxn introduction
The purpose of immune response is to eliminate the foreign antigens that have entered into the host. In most instances ,immune response leads to only a sub clinical or localise inflammatory response which just eliminates the antigen without causing significant damage to the host. However, at time, this response becomes abnormal leads to exaggerated inflammatory response which causes extensive tissue damage or sometimes even death.
Define hypersensitivity rxn
The term hypersensitivity or allergy refers to the injurious consequences in the sensitized host, following subsequent contact with specific antigens.
Gell and coombs classification
Immune response altered
Type 1- humoral
Type 2-humoral
Type 3- humoral
Type 4- cell mediated
Why in hypersensitivity rxn 1 immune response altered is humoral?
In hypersensitivity reactions type 1, the immune response is altered and is primarily a humoral immune response.
This means that when the body is exposed to an allergen (a substance that triggers an allergic reaction), it produces large amounts of a specific type of antibody called immunoglobulin E (IgE). IgE binds to receptors on the surface of mast cells, a type of immune cell found in many tissues, such as the skin and respiratory tract.
When the allergen is encountered again, it binds to the IgE on the mast cells, causing them to release large amounts of histamine and other inflammatory molecules. This results in the symptoms of an allergic reaction, such as itching, hives, swelling, and difficulty breathing.
The humoral immune response is responsible for the production of these IgE antibodies, which play a central role in the pathogenesis of type 1 hypersensitivity reactions. This type of reaction is also known as an immediate hypersensitivity reaction because it occurs within minutes to hours after exposure to the allergen
Why in hypersensitivity rxn 4 the immune response altered is cell mediated
In hypersensitivity reactions type 4, the immune response is altered and is primarily a cell-mediated immune response.
This means that when the body is exposed to an allergen or other foreign substance, a type of white blood cell called a T cell is activated. These T cells recognize and respond to the allergen by releasing cytokines and other chemical mediators that recruit and activate other immune cells, such as macrophages and cytotoxic T cells. These immune cells then attack and destroy the cells that are presenting the allergen.
Gell and coombs classification
Immediate or delayed
Type1- immediate
Type2-immediate
Type3-immediate
Type4-delayed
Gell and coombs classification
Duration between appearance of the symptom and contact of antigen
Type 1- 2-30 minutes
Type 2- 5-8 hours
Type 3- 2-8 hours
Type 4 - 24-72 hours
Gell and coombs classification
Antigen
Type 1- soluble
Type 2- cell surface bound
Type 3 - soluble
Type 4- soluble or bound
Type 1 hypersensitivity rxn
Type 1 hypersensitivity reaction is mediated by the antibody immunoglobulin E (IgE), which is produced by B cells in response to exposure to an allergen. When the allergen is encountered again, it binds to the IgE on the surface of mast cells and basophils, leading to their degranulation and release of histamine and other inflammatory mediators.
This process causes the symptoms of the allergic reaction, which can range from mild symptoms such as itching, sneezing, and hives to more severe symptoms such as anaphylaxis, which is a life-threatening reaction that can cause difficulty breathing, a drop in blood pressure, and loss of consciousness.
Examples of type 1 hypersensitivity reactions include hay fever, allergic asthma, and food allergies.
Overall, the immune response in type 1 hypersensitivity reactions is characterized by the production of IgE antibodies and the activation of mast cells and basophils, leading to the release of histamine and other inflammatory mediators. This process occurs rapidly, usually within minutes to hours of exposure to the allergen, and is responsible for the immediate symptoms of the allergic reaction
Gell and coombs classification
Effector mechanism(the effector mechanisms refer to the mechanisms by which immune cells, such as T cells, B cells, and antibodies, carry out their protective functions against invading pathogens. )
Type 1- mast cell degranulation
Type 2- ADCC(antibody dependent cellular cytotoxicity), complement mediated cytolysis
Type 3- complement activation and inflammatory response
Type4- macrophage activation leads to phagocytosis and cell cytotoxicity
Type 2 hypersensitivity reaction
Type 2 hypersensitivity, which is also known as antibody-mediated hypersensitivity. In this type of hypersensitivity reaction, the immune response is mediated by IgG or IgM antibodies that bind to antigens on the surface of cells or tissues. This binding can activate complement proteins or lead to antibody-dependent cell-mediated cytotoxicity (ADCC), which involves the destruction of cells by immune cells that recognize them as foreign.
Examples of type 2 hypersensitivity reactions include autoimmune diseases such as rheumatoid arthritis and systemic lupus erythematosus, as well as some drug reactions and blood transfusion reactions.
It’s important to note that while the classification of hypersensitivity reactions into four types is useful for understanding the mechanisms involved, in reality, many allergic and autoimmune reactions involve a combination of different types of immune responses.
Type 3 hypersensitivity reaction
Type III hypersensitivity reaction, also known as immune complex-mediated hypersensitivity, occurs when immune complexes are formed by the interaction between soluble antigens and antibodies, usually IgG. These immune complexes can accumulate in various tissues, leading to inflammation and tissue damage.
In Type III hypersensitivity reactions, the immune complexes activate complement proteins, which attract immune cells to the site of inflammation. This leads to the release of inflammatory mediators such as histamine, prostaglandins, and cytokines, which cause tissue damage and inflammation.
Examples of Type III hypersensitivity reactions include serum sickness, certain drug reactions, and some autoimmune diseases such as systemic lupus erythematosus.
It’s important to note that while immune complexes are normally cleared from the body, in Type III hypersensitivity reactions, the immune complexes are not cleared properly and accumulate in tissues, leading to chronic inflammation and tissue damage.
Type 4 hypersensitivity reaction
Delayed hypersensitivity reaction, also known as Type IV hypersensitivity reaction, is a type of abnormal cell-mediated immune response that occurs several days after exposure to an antigen. This response is mediated by a specific subset of T cells called delayed hypersensitivity T cells, or T helper 1 cells (Th1 cells).
In Type IV hypersensitivity reactions, the Th1 cells recognize the antigen and release cytokines, which activate macrophages and recruit other immune cells such as neutrophils and T cells to the site of inflammation. This results in tissue damage and inflammation, which can lead to a variety of symptoms depending on the location of the reaction.
Examples of Type IV hypersensitivity reactions include contact dermatitis, such as poison ivy or metal allergies, and some autoimmune diseases such as multiple sclerosis and type 1 diabetes.
Unlike Type I-III hypersensitivity reactions, which occur rapidly, Type IV hypersensitivity reactions take several days to develop, which is why they are called “delayed” hypersensitivity reactions
Gell and coomb classification
Desensitisation of the allergen
Type 1 - easy and short lasting
Type 2- easy and short lasting
Type 3- easy and short lasting
Type 4- difficult but sustained
Type 1 hypersensitivity reaction elaborate
The hallmark of type I hypersensitivity reaction, also known as immediate hypersensitivity or allergic reaction, is the production of IgE antibodies by sensitized B cells in response to an allergen. These IgE antibodies then bind to specific receptors on the surface of mast cells and basophils, leading to their activation and degranulation.
The degranulation of mast cells and basophils releases pharmacologically active mediators such as histamine, leukotrienes, and prostaglandins, which cause vasodilation, vascular and smooth muscle contraction, and increased vascular permeability. These changes ultimately lead to localized responses such as itching, redness, and swelling, which are known as atopic responses, and in severe cases, a systemic response known as anaphylaxis.
Type I hypersensitivity reactions can occur in response to a variety of allergens, including pollen, animal dander, food, and medications. They are typically rapid-onset and can be life-threatening in severe cases. Treatment may include avoiding the allergen, medications to manage symptoms, and in some cases, allergen immunotherapy (desensitization)
