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Hypersensitivity
Hypersensitivity (also called hypersensitivity reaction or intolerance) is an abnormal physiological condition in which there is an undesirable and adverse immune response to an antigen. It is an abnormality in the immune system that causes Immune disorder, immune diseases including allergies and autoimmunity. It is caused by many types of particles and substances from the external environment or from within the body that are recognized by the immune cells as antigens. The immune reactions are usually referred to as an over-reaction of the immune system and they are often damaging and uncomfortable. In 1963, Philip George Houthem Gell and Robin Coombs introduced a systematic classification of the different types of hypersensitivity based on the types of antigens and immune responses involved. According to this system, known as the #Gell and Coombs classification, Gell and Coombs classification or Gell-Coombs's classification, there are four types of hypersensitivity, namely: Typ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Type I Hypersensitivity
Type I hypersensitivity (or immediate hypersensitivity), in the Hypersensitivity, Gell and Coombs classification of allergic reactions, is an allergic reaction provoked by re-exposure to a specific type of antigen referred to as an allergen. Type I is distinct from Type II hypersensitivity, type II, Type III hypersensitivity, type III and Type IV hypersensitivity, type IV hypersensitivities. The relevance of the Gell and Coombs classification of allergic reactions has been questioned in the modern-day understanding of allergy, and it has limited utility in clinical practice. Exposure may be by ingestion, inhalation, injection (medicine), injection, or direct contact. Pathophysiology In type I hypersensitivity, B cell, B cells are stimulated (by T helper cell#Th1/Th2 model, CD4+ Th2 cells) to produce IgE antibodies specific to an antigen. The difference between a normal infectious immune response and a type 1 hypersensitivity response is that in type 1 hypersensitivity, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Type IV Hypersensitivity
Type IV hypersensitivity, in the Gell and Coombs classification of allergic reactions, often called delayed-type hypersensitivity, is a type of hypersensitivity reaction that can take a day or more to develop. Unlike the other types, it is not humoral (not antibody-mediated) but rather is a type of cell-mediated response. This response involves the interaction of T cells, monocytes, and macrophages. This reaction is caused when CD4+ Th1 cells recognize foreign antigen in a complex with the MHC class II on the surface of antigen-presenting cells. These can be macrophages that secrete IL-12, which stimulates the proliferation of further CD4+ Th1 cells. CD4+ T cells secrete IL-2 and interferon gamma (IFNγ), inducing the further release of other Th1 cytokines, thus mediating the immune response. Activated CD8+ T cells destroy target cells on contact, whereas activated macrophages produce hydrolytic enzymes and, on presentation with certain intracell ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Type III Hypersensitivity
Type III hypersensitivity, in the Gell and Coombs classification of allergic reactions, occurs when there is accumulation of immune complexes (antigen-antibody complexes) that have not been adequately cleared by innate immune cells, giving rise to an inflammatory response and attraction of leukocytes. There are three steps that lead to this response. The first step is immune complex formation, which involves the binding of antigens to antibodies to form mobile immune complexes. The second step is immune complex deposition, during which the complexes leave the plasma and are deposited into tissues. Finally, the third step is the inflammatory reaction, during which the classical pathway is activated and macrophages and neutrophils are recruited to the affected tissues. Such reactions may progress to immune complex diseases. Types Some clinical examples: Other examples are: * Subacute bacterial endocarditis * Symptoms of malaria Pathogenesis Gel and Coombs defined type III ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Type II Hypersensitivity
Type II hypersensitivity, in the Gell and Coombs classification of allergic reactions, is an antibody-mediated process in which IgG and IgM antibodies are directed against antigens on cells (such as circulating red blood cells) or extracellular material (such as basement membrane). This subsequently leads to cell lysis, tissue damage or loss of function through mechanisms such as # complement activation via the classical complement pathway # Antibody-dependent cellular cytotoxicity or # anti-receptor activity. The activation of the complement system results in opsonization, the agglutination of red blood cells, cell lysis, and cell death. These reactions usually take between 2 and 24 hours to develop. Examples An example of complement dependent type II hypersensitivity is an acute hemolytic transfusion reaction following transfusion of ABO incompatible blood. Preformed antibody (predominantly IgM) against donor red cell antigens not found in an individual of a partic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anaphylaxis
Anaphylaxis (Greek: 'up' + 'guarding') is a serious, potentially fatal allergic reaction and medical emergency that is rapid in onset and requires immediate medical attention regardless of the use of emergency medication on site. It typically causes more than one of the following: an itchy rash, throat closing due to swelling that can obstruct or stop breathing; severe tongue swelling that can also interfere with or stop breathing; shortness of breath, vomiting, lightheadedness, loss of consciousness, low blood pressure, and medical shock. These symptoms typically start in minutes to hours and then increase very rapidly to life-threatening levels. Urgent medical treatment is required to prevent serious harm and death, even if the patient has used an epinephrine autoinjector or has taken other medications in response, and even if symptoms appear to be improving. Cause, mechanism, and diagnosis Common causes include allergies to insect bites and stings, allergies to fo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Immune System
The immune system is a network of biological systems that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to bacteria, as well as Tumor immunology, cancer cells, Parasitic worm, parasitic worms, and also objects such as wood splinters, distinguishing them from the organism's own healthy biological tissue, tissue. Many species have two major subsystems of the immune system. The innate immune system provides a preconfigured response to broad groups of situations and stimuli. The adaptive immune system provides a tailored response to each stimulus by learning to recognize molecules it has previously encountered. Both use humoral immunity, molecules and cell-mediated immunity, cells to perform their functions. Nearly all organisms have some kind of immune system. Bacteria have a rudimentary immune system in the form of enzymes that protect against bacteriophage, viral infections. Other basic immune mechanisms evolved in ancien ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Atopy
Atopy is the tendency to produce an exaggerated immunoglobulin E (IgE) immune response to otherwise harmless substances in the environment. Allergic diseases are clinical manifestations of such inappropriate, atopic responses. Atopy may have a hereditary component, although contact with the allergen or irritant must occur before the hypersensitivity reaction can develop (characteristically after re-exposure). Maternal psychological trauma during pregnancy may also be a strong indicator for development of atopy. The term ''atopy'' was coined by Arthur F. Coca and Robert Cooke in 1923 from the Greek ἀτοπία meaning "the state of being out of place", "absurdity". Many physicians and scientists use the term ''atopy'' for any reaction mediated by IgE (even those that are appropriate and proportional to the antigen), but many pediatricians reserve it to refer only to a genetically mediated predisposition to an excessive IgE reaction. Signs and symptoms Atopic sensitiz ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Immunology
Immunology is a branch of biology and medicine that covers the study of Immune system, immune systems in all Organism, organisms. Immunology charts, measures, and contextualizes the Physiology, physiological functioning of the immune system in states of both health and diseases; malfunctions of the immune system in immunological disorders (such as Autoimmune disease, autoimmune diseases, Hypersensitivity, hypersensitivities, immune deficiency, and transplant rejection); and the physical, chemical, and physiological characteristics of the components of the immune system ''in vitro'', ''In situ#Biology and biomedical engineering, in situ'', and ''in vivo''. Immunology has applications in numerous disciplines of medicine, particularly in the fields of organ transplantation, oncology, rheumatology, virology, bacteriology, parasitology, psychiatry, and dermatology. The term was coined by Russian biologist Ilya Ilyich Mechnikov, who advanced studies on immunology and received the Nob ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Antibody-dependent Cell-mediated Cytotoxicity
Antibody-dependent cellular cytotoxicity (ADCC), also referred to as antibody-dependent cell-mediated cytotoxicity, is a mechanism of Cell-mediated immunity, cell-mediated immune defense whereby an effector cell of the immune system kills a target cell, whose membrane-surface antigens have been bound by specific antibodies. It is one of the mechanisms through which antibodies, as part of the humoral immunity, humoral immune response, can act to limit and contain infection. ADCC is independent of the immune complement system that also lyses targets but does not require any other cell. ADCC requires an effector cell which classically is known to be natural killer cell, natural killer (NK) cells that typically interact with immunoglobulin G (IgG) antibodies. However, macrophages, neutrophils and eosinophils can also mediate ADCC, such as eosinophils killing certain parasitic worms known as helminths via IgE antibodies. In general, ADCC has typically been described as the immune respo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Allergy
Allergies, also known as allergic diseases, are various conditions caused by hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include Allergic rhinitis, hay fever, Food allergy, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis. Symptoms may include allergic conjunctivitis, red eyes, an itchy rash, sneeze, sneezing, coughing, a rhinorrhea, runny nose, shortness of breath, or swelling. Note that food intolerances and food poisoning are separate conditions. Common allergens include pollen and certain foods. Metals and other substances may also cause such problems. Food, insect stings, and medications are common causes of severe reactions. Their development is due to both genetic and environmental factors. The underlying mechanism involves immunoglobulin E antibodies (IgE), part of the body's immune system, binding to an allergen and then to FcεRI, a receptor on mast cells or basophils where it triggers ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Autoimmunity
In immunology, autoimmunity is the system of immune responses of an organism against its own healthy cells, tissues and other normal body constituents. Any disease resulting from this type of immune response is termed an " autoimmune disease". Prominent examples include celiac disease, diabetes mellitus type 1, Henoch–Schönlein purpura, systemic lupus erythematosus, Sjögren syndrome, eosinophilic granulomatosis with polyangiitis, Hashimoto's thyroiditis, Graves' disease, idiopathic thrombocytopenic purpura, Addison's disease, rheumatoid arthritis, ankylosing spondylitis, polymyositis, dermatomyositis, and multiple sclerosis. Autoimmune diseases are very often treated with steroids. Autoimmunity means presence of antibodies or T cells that react with self-protein and is present in all individuals, even in normal health state. It causes autoimmune diseases if self-reactivity can lead to tissue damage. History In the later 19th century, it was believed that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Allergies
Allergies, also known as allergic diseases, are various conditions caused by hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include Allergic rhinitis, hay fever, Food allergy, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis. Symptoms may include allergic conjunctivitis, red eyes, an itchy rash, sneeze, sneezing, coughing, a rhinorrhea, runny nose, shortness of breath, or swelling. Note that food intolerances and food poisoning are separate conditions. Common allergens include pollen and certain foods. Metals and other substances may also cause such problems. Food, insect stings, and medications are common causes of severe reactions. Their development is due to both genetic and environmental factors. The underlying mechanism involves immunoglobulin E antibodies (IgE), part of the body's immune system, binding to an allergen and then to FcεRI, a receptor on mast cells or basophils where it triggers ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
