Immunologie deel 2 2025 20.2.pptx

# Tissue transplantation and immune rejection Tissue transplantation and immune rejection represent a critical area of immunology where the body's defense mechanisms must be carefully managed to accept foreign tissues. This section delves into the fundamental principles governing transplant compatibility, the pivotal role of the Major Histocompatibility Complex (MHC) in self-non-self discrimination, and the essential strategies employed to prevent graft rejection, primarily through immunosuppression. ## 1. Tissue transplantation and immune rejection ### 1.1 Introduction to tissue transplantation Tissue transplantation involves replacing a diseased or damaged organ or tissue with a healthy one, offering a life-saving or life-improving intervention. This can occur between individuals (allograft) or even within the same individual (autograft), for example, using skin grafts to treat severe burns or reconstructive procedures following radiation therapy. Various tissues can be transplanted, including skin, segments of the small intestine, cartilage, bone tissue, ocular tissue, heart valves, blood vessels, and nerve tissue. ### 1.2 The challenge of immune rejection A primary challenge in tissue transplantation is the potential for the recipient's immune system to recognize and reject the transplanted tissue. This rejection occurs because glycoproteins on the surface of the transplanted cells are perceived as foreign antigens by the recipient's immune system. ### 1.3 The Major Histocompatibility Complex (MHC) system The MHC system plays a crucial role in distinguishing self from non-self. It comprises a collection of proteins found on the surface of cells that exhibit slight variations between individuals. #### 1.3.1 Function of MHC The MHC acts as an "identity card" for each individual, enabling the immune system to differentiate between the body's own cells and foreign invaders. #### 1.3.2 Human Leukocyte Antigen (HLA) In humans, the MHC system is referred to as the Human Leukocyte Antigen (HLA) system. These markers are highly individual and are typically identical only in identical twins. #### 1.3.3 Histocompatibility Histocompatibility refers to the degree of compatibility between tissues or organs from different individuals. A higher degree of histocompatibility reduces the likelihood of immune rejection. However, even with maximal histocompatibility, immunosuppression is usually necessary to prevent rejection. > **Tip:** Understanding MHC/HLA matching is fundamental to successful organ transplantation, with efforts always made to find the closest possible match between donor and recipient. ### 1.4 Immunosuppression To prevent the immune system from rejecting transplanted tissues, immunosuppressive medications, known as immunosuppressants, are administered. #### 1.4.1 Necessity and duration of immunosuppression Immunosuppressants must typically be taken for the remainder of the recipient's life. The dosage is often adjusted over time to strike a balance between preventing rejection and minimizing the side effects of the medication. > **Tip:** Balancing the need for immunosuppression to prevent rejection against the risks of increased infection and other side effects is a key challenge in transplant management. ### 1.5 Blood transfusions and the immune system The principles of transplant rejection are also evident in blood transfusions, particularly concerning blood groups. #### 1.5.1 Blood groups and agglutination Historically, mismatched blood transfusions led to severe reactions, including blood clotting (agglutination). Karl Landsteiner's work in the early 20th century identified glycoproteins on the surface of red blood cells as the basis for different blood groups. #### 1.5.2 ABO blood group system The ABO blood group system is determined by the presence or absence of A and B antigens (agglutinogens) on red blood cells and corresponding antibodies (anti-A and anti-B) in the plasma. * Individuals with blood type A have A antigens and anti-B antibodies. * Individuals with blood type B have B antigens and anti-A antibodies. * Individuals with blood type AB have both A and B antigens and neither anti-A nor anti-B antibodies. * Individuals with blood type O have neither A nor B antigens and both anti-A and anti-B antibodies. #### 1.5.3 The Rh system In addition to the ABO system, the Rhesus (Rh) factor, specifically the D antigen (agglutinogen D), is important. * Individuals who possess the D antigen are Rh-positive (Rh+). * Individuals who lack the D antigen are Rh-negative (Rh-). #### 1.5.4 Rh incompatibility and pregnancy Rh incompatibility can cause problems during pregnancy if an Rh-negative mother carries an Rh-positive fetus. The first contact with fetal blood can induce the mother to produce anti-Rh antibodies. In subsequent pregnancies with an Rh-positive fetus, these antibodies can cross the placenta and cause the breakdown of fetal red blood cells, leading to hemolytic disease of the newborn (erythroblastosis fetalis), characterized by jaundice. This is managed by administering anti-Rh serum to the mother. > **Example:** An Rh-negative mother carrying her first Rh-positive child may not experience issues. However, if she later becomes pregnant with another Rh-positive child, her pre-existing anti-Rh antibodies can attack the fetus's red blood cells, causing a severe reaction. This is preventable with Rh immunoglobulin injections. --- # Blood groups and transfusion This topic explores the crucial concepts of blood groups, focusing on the ABO and Rh systems, the underlying mechanisms of agglutination, and the historical context and associated risks of blood transfusions. ### 2.1 Blood groups and antigens Blood groups are determined by the presence or absence of specific glycoproteins on the plasma membrane of erythrocytes (red blood cells). These glycoproteins act as antigens, which are molecules recognized by the immune system. #### 2.1.1 The ABO system The ABO blood group system is based on the presence of two main antigens: antigen A and antigen B. * **Blood group A:** Possesses antigen A on erythrocytes and anti-B antibodies in the plasma. * **Blood group B:** Possesses antigen B on erythrocytes and anti-A antibodies in the plasma. * **Blood group AB:** Possesses both antigen A and antigen B on erythrocytes, and no anti-A or anti-B antibodies in the plasma. * **Blood group O:** Possesses neither antigen A nor antigen B on erythrocytes, but has both anti-A and anti-B antibodies in the plasma. These blood groups are genetically determined and can be understood through Mendelian inheritance patterns. #### 2.1.2 Agglutination Agglutination, or the clumping of red blood cells, is a key process in blood transfusion reactions. It occurs when antibodies in the recipient's plasma bind to corresponding antigens on the donor's red blood cells, causing them to aggregate. This is a direct consequence of the immune system recognizing foreign antigens. > **Tip:** Understanding the antigen-antibody combinations is vital for safe blood transfusions. Mismatched transfusions can lead to severe and life-threatening agglutination. ### 2.2 The Rh system The Rh system, named after the Rhesus monkey, is another important blood group system. It is primarily determined by the presence or absence of the D antigen (Rh factor). * **Rh-positive (Rh+):** Individuals possess the D antigen on their erythrocytes. * **Rh-negative (Rh-):** Individuals lack the D antigen on their erythrocytes. Unlike the ABO system, individuals who are Rh-negative do not spontaneously produce anti-Rh antibodies. However, they can develop these antibodies upon exposure to Rh-positive blood. #### 2.2.1 Rh incompatibility during pregnancy A significant concern arises when an Rh-negative mother is pregnant with an Rh-positive fetus. During pregnancy or delivery, some of the fetus's Rh-positive blood can enter the mother's bloodstream. This exposure can trigger the mother's immune system to produce anti-Rh antibodies. If the mother becomes pregnant with a subsequent Rh-positive child, these pre-existing anti-Rh antibodies can cross the placenta and attack the fetus's red blood cells, leading to a condition known as hemolytic disease of the newborn, characterized by jaundice and anemia due to the destruction of fetal red blood cells (hemolysis). > **Tip:** This Rh incompatibility issue is managed by administering Rh immunoglobulin (Rhogam) to Rh-negative mothers during pregnancy and after delivery to prevent antibody formation. ### 2.3 Blood transfusions: historical context and risks Historically, blood transfusions were performed without a full understanding of blood groups, often leading to fatal outcomes due to agglutination. The discovery of blood groups by Karl Landsteiner in the early 1900s revolutionized transfusion medicine, allowing for safer and more effective treatments. Despite advancements, blood transfusions still carry risks: * **Agglutination and Hemolysis:** Mismatched ABO or Rh blood types can lead to severe agglutination and destruction of transfused red blood cells, causing a potentially fatal transfusion reaction. * **Allergic Reactions:** Some individuals may experience allergic reactions to components in the transfused blood. * **Infections:** Although rare due to rigorous screening, there is a minimal risk of transmitting infectious diseases through blood transfusions. * **Volume Overload:** Transfusing blood too rapidly can lead to circulatory overload, particularly in individuals with cardiac or renal issues. > **Example:** A person with blood group A (who has anti-B antibodies) receiving blood from a person with blood group B (who has B antigens) would experience severe agglutination as the anti-B antibodies attack the B antigens on the donor's red blood cells. --- # Allergic reactions and hypersensitivity Allergic reactions, also known as hypersensitivity, are exaggerated immune responses to substances that are typically harmless. ### 3.1 Mechanisms of allergic reactions Allergic reactions involve a two-step process: 1. **Sensitization:** The first exposure to an allergen leads to the formation of specific antibodies, primarily immunoglobulin E (IgE). These IgE antibodies then bind to the surface of white blood cells called mast cells. 2. **Re-exposure and Activation:** Upon subsequent exposure to the same allergen, the allergen binds to the IgE antibodies on the mast cells. This triggers the release of chemical mediators, such as histamine, from the mast cells. The release of these mediators causes the characteristic symptoms of an allergic reaction. If the allergen enters the bloodstream directly, a rapid and severe reaction, known as anaphylactic shock, can occur. ### 3.2 Allergens and Common Allergens Allergens are substances that can trigger an allergic reaction in susceptible individuals. #### 3.2.1 Pollen * Pollen from wind-pollinated plants (grasses, herbs, trees with catkins) is a common cause of hay fever (allergic rhinitis). * Hay fever symptoms typically manifest when pollen concentration reaches about fifty grains per cubic meter. * Rainfall can reduce pollen concentrations. * Pollen grains coming into contact with nasal or ocular mucous membranes initiate the reaction. #### 3.2.2 Latex * Latex allergies can be classified into two types: * **Type I latex allergy:** This is a reaction to natural rubber latex, which can cause hives, allergic nasal and eye symptoms, and asthma. * **Type IV latex allergy:** This is a delayed-type contact allergic eczema caused by chemical additives in rubber. Symptoms include hives, bumps, blisters, redness, and itching. * Latex is found in products such as household gloves, condoms, balloons, pacifiers, and air mattresses. * Cross-reactivity with other plant-based products like bananas, kiwis, and avocados can occur. #### 3.2.3 House dust mites * These are arachnids that thrive in warm, humid environments, particularly in mattresses. * Allergies are typically caused by substances in the mites' feces, not by the mites themselves. ### 3.3 Symptoms of Allergic Reactions The symptoms of allergic reactions can vary widely and may include: * Hives (urticaria) * Swelling (angioedema) * Tingling sensations in the mouth and throat * Nasal congestion or runny nose (rhinitis) * Red, irritated eyes * Abdominal cramps * Nausea, vomiting, and diarrhea * Asthma * Anaphylactic shock (a severe, life-threatening reaction) ### 3.4 Diagnosis of Allergies Allergies can be diagnosed using several methods: * **Skin prick test and patch test:** Small amounts of suspected allergens are applied to the skin to observe for a localized reaction. * **Blood test:** This test can detect the presence of IgE antibodies specific to certain allergens. ### 3.5 Treatment of Allergies Treatment strategies aim to manage symptoms and reduce the immune system's reactivity: * **Antihistamines:** These medications block the action of histamine, preventing or reducing allergic symptoms. * **Topical corticosteroids:** Creams and ointments containing corticosteroids are used to treat inflammatory conditions like atopic eczema. * **Bronchodilators:** These drugs relax the smooth muscles in the airways, relieving bronchoconstriction associated with asthma. * **Adrenaline (epinephrine) injection:** This is a life-saving emergency treatment for severe reactions like anaphylactic shock, providing a temporary solution. * **Immunotherapy:** This involves administering increasing doses of the allergen over time to desensitize the immune system, aiming for long-term reduction or elimination of allergic responses. ### 3.6 Conditions Mistaken for Allergies * **Lactose intolerance:** This is **not** an allergy. It is caused by a deficiency in the enzyme lactase, which leads to an inability to digest lactose. Undigested lactose is then fermented by gut bacteria, causing digestive symptoms. There are primary (age-related decrease), secondary (due to gut damage), and congenital (genetic) forms of lactose intolerance. ### 3.7 Autoimmune Reactions In autoimmune reactions, the T-lymphocytes mistakenly target and attack the body's own antigens. This can lead to programmed cell death (apoptosis) of the body's own cells or trigger an immune response against the body itself, resulting in autoimmune diseases. Examples include rheumatoid arthritis, multiple sclerosis (where myelin is attacked), and psoriasis. > **Tip:** While the document briefly mentions apoptosis versus necrosis, for the context of allergies and hypersensitivity, focus on how the immune system's misdirected responses cause issues, rather than the specific cell death mechanisms unless directly linked to an allergic process. ### 3.8 Other Immune-Related Conditions Mentioned * **Infectious Mononucleosis (Glandular Fever/Mononucleosis):** Caused by the Epstein-Barr virus (EBV), which infects B-lymphocytes. The immune system responds by activating macrophages and T-cells to attack infected B-cells, which also produce antibodies against EBV. EBV can remain latent in the body. Treatment focuses on rest and symptom management. * **Lymphoma:** A cancer of the lymphatic system, originating from uncontrolled division of lymphocytes. The two main types are Hodgkin lymphoma and Non-Hodgkin lymphoma. Symptoms include a weakened immune system, increased susceptibility to infections, and enlarged lymph nodes. Diagnosis involves blood tests, biopsies, and imaging. Treatment may include chemotherapy, immunotherapy, radiation, or stem cell transplantation, depending on the type and stage. --- # Autoimmune diseases and immune system disorders This section delves into conditions where the immune system malfunctions, attacking the body's own tissues or developing cancerous growths, alongside viral infections that impact immune responses. ### 4.1 Autoimmune reactions Autoimmune diseases occur when the immune system mistakenly identifies the body's own components as foreign invaders and launches an attack against them. This can lead to chronic inflammation and damage to various organs and tissues. #### 4.1.1 Examples of autoimmune diseases * **Rheumatoid arthritis:** An autoimmune condition that primarily affects the joints, causing inflammation, pain, stiffness, and eventual joint damage. * **Multiple sclerosis:** An autoimmune disease that attacks the central nervous system, specifically the myelin sheath that insulates nerve fibers. This damage disrupts nerve signal transmission, leading to a wide range of neurological symptoms. * **Psoriasis:** An autoimmune condition characterized by the rapid buildup of skin cells, resulting in thick, silvery scales and itchy, dry, red patches. #### 4.1.2 Apoptosis versus necrosis in autoimmune responses The immune system has mechanisms to eliminate self-reactive cells. * **Apoptosis** is programmed cell death, a controlled process where cells self-destruct. In the context of autoimmune diseases, if T-lymphocytes recognize self-antigens, they are supposed to undergo apoptosis to prevent an autoimmune response. * **Necrosis** is uncontrolled cell death, often due to injury or disease, which can lead to inflammation and damage. ### 4.2 Viral infections affecting the immune system Certain viruses can directly impact the immune system, either by infecting immune cells or by triggering specific immune responses. #### 4.2.1 Infectious mononucleosis (glandular fever) * **Cause:** Epstein-Barr virus (EBV). * **Transmission:** Primarily through saliva, often referred to as the "kissing disease." * **Symptoms:** Fatigue, fever, and swollen lymph nodes. * **Immune system interaction:** EBV infects B-lymphocytes, leading to the activation of the immune system. Macrophages recognize the virus as part of the innate immune response, while T-cells target infected B-cells. B-cells produce antibodies against EBV. * **Latent infection:** EBV remains latent in the body after recovery. * **Treatment:** There is no specific medication; treatment focuses on rest and symptom management. * **Long-term consequences (rare):** Chronic fatigue and an increased risk of certain immune diseases. ### 4.3 Lymphomas (lymph cancers) Lymphomas are a group of cancers that originate in the lymphatic system, which is part of the immune system. They arise from the uncontrolled proliferation of lymphocytes. #### 4.3.1 Types of lymphoma * **Hodgkin lymphoma:** A less common type, characterized by the presence of specific Reed-Sternberg cells. * **Non-Hodgkin lymphoma:** A more common and diverse group, encompassing many different subtypes. #### 4.3.2 Pathogenesis of lymphoma Normal B or T cells transform into cancerous cells. These cancer cells divide uncontrollably and accumulate in lymph nodes, the spleen, and bone marrow. #### 4.3.3 Consequences of lymphoma * **Weakened immune system:** Impaired ability to fight off infections. * **Enlarged lymph nodes:** A common clinical sign. #### 4.3.4 Diagnosis and treatment * **Diagnosis:** Blood tests, lymph node biopsies, and imaging techniques such as CT, MRI, and PET scans. * **Treatment:** Chemotherapy, immunotherapy (specifically targeting immune cells), radiation therapy, or stem cell transplantation in severe cases. The treatment approach depends on the specific type and stage of the cancer. ### 4.4 Allergies (hypersensitivity reactions) Allergies are exaggerated immune responses to otherwise harmless substances called allergens. Approximately one in five people experiences allergies. #### 4.4.1 Allergens and symptoms * **Allergens:** Substances that trigger an oversensitive immune response. * **Symptoms:** Can vary widely and include hives, swelling, tingling in the mouth and throat, nasal congestion or runny nose, red and irritated eyes, abdominal cramps, nausea, vomiting, diarrhea, and asthma. Severe reactions can lead to anaphylactic shock. #### 4.4.2 Mechanism of allergic reactions Allergic reactions typically involve two steps: 1. **Sensitization:** The first exposure to an allergen leads to the production of specific antibodies called Immunoglobulin E (IgE). These IgE antibodies bind to mast cells, which are a type of white blood cell. 2. **Elicitation:** Upon subsequent exposure to the same allergen, it binds to the IgE on mast cells, triggering the release of histamine and other inflammatory mediators. This causes the allergic symptoms. * **Anaphylactic shock:** A rapid and severe systemic allergic reaction that can be life-threatening. It occurs when the allergen enters the bloodstream directly. #### 4.4.3 Diagnosis of allergies * **Skin prick test:** Small amounts of suspected allergens are pricked into the skin to observe for localized reactions. * **Patch test:** Used for contact allergies, where allergens are applied to the skin under a patch. * **Blood test:** Detects the presence of IgE antibodies specific to certain allergens. #### 4.4.4 Treatment of allergies * **Antihistamines:** Block the action of histamine, reducing allergic symptoms. * **Topical corticosteroids:** Creams or ointments used for conditions like eczema. * **Bronchodilators:** Relax the smooth muscles in the airways, relieving asthma symptoms. * **Adrenaline injection:** An emergency treatment for anaphylactic shock. * **Immunotherapy (allergy shots):** Involves gradually increasing doses of the allergen to desensitize the immune system over time. #### 4.4.5 Common allergens * **Pollen:** Causes hay fever, particularly from wind-pollinated plants like grasses, herbs, and trees. Pollen grains contacting nasal or eye tissues trigger the reaction. * **Profilin:** An allergen found in plants, often associated with allergies to latex and other plant-based products, leading to cross-reactivity (e.g., with bananas, kiwi, avocado). * **Latex:** Can cause reactions to natural rubber products like gloves, condoms, and balloons. * **Type I latex allergy:** A reaction to natural rubber, causing symptoms like hives, nasal and eye irritation, and asthma. * **Type IV latex allergy:** A delayed reaction to chemical additives in rubber, causing contact dermatitis with redness, itching, blisters, and bumps. * **House dust mites:** Microscopic arachnids found in warm, humid environments. Allergies are typically to substances in their feces, not the mites themselves. * **Lactose intolerance:** **Crucially, this is NOT an allergy.** It is a deficiency in the enzyme lactase, which is needed to digest lactose. Undigested lactose is fermented by gut bacteria, causing digestive issues. It can be primary (decreasing production after age three), secondary (due to gut damage), or congenital (a rare genetic defect). ### 4.5 Tissue transplantation and histocompatibility Tissue transplantation involves replacing diseased or damaged tissue with healthy tissue, which can be from a deceased donor or within the same individual. #### 4.5.1 Histocompatibility complex (MHC) * **Definition:** The Major Histocompatibility Complex (MHC) is a collection of proteins found on the surface of cells. These proteins differ slightly between individuals and act as a unique molecular "identity card" for each person. * **Function:** The MHC system helps the immune system distinguish between the body's own cells ("self") and foreign invaders ("non-self"). In humans, MHC molecules are also known as Human Leukocyte Antigens (HLA). * **Identicality:** MHC molecules are only identical in identical twins. #### 4.5.2 Histocompatibility * **Definition:** Histocompatibility refers to the compatibility of tissues for transplantation, meaning how likely they are to be accepted by the recipient's immune system. * **Compatibility:** High histocompatibility is crucial for successful transplantation. It is highest between identical twins. * **Immune suppression:** Even with high histocompatibility, some degree of immune suppression is usually necessary to prevent the recipient's immune system from rejecting the transplanted tissue. #### 4.5.3 Immunosuppressants Immunosuppressants are medications used to suppress the immune system. They are typically required for life after a transplant to prevent rejection. Doses may be adjusted over time to balance the prevention of rejection with the management of side effects. ### 4.6 Blood transfusions and blood groups Blood transfusions involve the transfer of blood or blood components from one individual to another. #### 4.6.1 Blood groups * **Discovery:** Karl Landsteiner discovered blood groups in 1900, identifying glycoproteins on the surface of red blood cells (erythrocytes) that determine blood type. * **ABO system:** Based on the presence or absence of A and B antigens on red blood cells. * **Blood group A:** Has A antigens and produces anti-B antibodies. * **Blood group B:** Has B antigens and produces anti-A antibodies. * **Blood group AB:** Has both A and B antigens and produces no anti-A or anti-B antibodies. * **Blood group O:** Has neither A nor B antigens and produces both anti-A and anti-B antibodies. * **Agglutination:** If incompatible blood types are mixed, antibodies in the recipient's plasma will bind to antigens on the donor's red blood cells, causing them to clump together (agglutinate), which can be dangerous. * **Genetic determination:** Blood groups are genetically determined and can be predicted using inheritance patterns. #### 4.6.2 Rhesus factor (Rh factor) * **Definition:** In addition to the ABO system, the Rhesus factor is determined by the presence or absence of the D antigen (agglutinogen D) on red blood cells. * **Rh-positive (Rh+):** Individuals with the D antigen. * **Rh-negative (Rh-):** Individuals without the D antigen. They do not spontaneously produce anti-Rh antibodies. * **Sensitization:** An Rh-negative person can become sensitized and produce anti-Rh antibodies if exposed to Rh-positive blood. * **Rhesus disease of the newborn:** A potential problem arises during pregnancy if an Rh-negative mother is carrying an Rh-positive baby. Exposure to the baby's blood can lead to the mother developing anti-Rh antibodies. In subsequent pregnancies with an Rh-positive fetus, these antibodies can cross the placenta and attack the baby's red blood cells, causing hemolysis and jaundice. * **Prevention:** This can be prevented by administering serum containing anti-Rh antibodies to the mother during and after pregnancy. --- ## Common mistakes to avoid - Review all topics thoroughly before exams - Pay attention to formulas and key definitions - Practice with examples provided in each section - Don't memorize without understanding the underlying concepts

| Term | Definition | |------|------------| | Tissue transplantation | The process of replacing a diseased or damaged tissue with a healthy one, which can be from a deceased donor or within the same individual. | | Major Histocompatibility Complex (MHC) | A group of proteins on the surface of cells that helps the immune system distinguish between self and non-self tissues. In humans, these are known as Human Leukocyte Antigens (HLA). | | Histocompatibility | The compatibility of tissues between individuals, which determines the likelihood of successful transplantation without rejection. This is highest in identical twins. | | Immunosuppressants | Medications used to suppress the immune system's response, essential for preventing the rejection of transplanted tissues or organs. These are often required for a lifetime. | | Agglutination | The clumping of particles, such as blood cells, which occurs when antibodies bind to antigens on their surface, a process crucial for understanding blood group compatibility. | | Erythrocytes | Red blood cells, which contain specific glycoproteins on their plasma membrane that determine blood groups. | | Antigens | Molecules, often glycoproteins, on the surface of cells that are recognized by the immune system as foreign or "non-self," triggering an immune response. | | Antibodies | Proteins produced by the immune system (specifically B cells) that recognize and bind to specific antigens, helping to neutralize or eliminate foreign substances. | | Rh factor | A blood group antigen (specifically antigen D) found on red blood cells. Individuals are classified as Rh-positive if they have it and Rh-negative if they do not. | | Hemolysis | The rupture or lysis of red blood cells, which can occur during an incompatible blood transfusion or in certain medical conditions, leading to the release of hemoglobin. | | Allergens | Substances that can trigger an allergic reaction in susceptible individuals by provoking an exaggerated immune response from the body's defense system. | | IgE | Immunoglobulin E, a type of antibody that plays a key role in allergic reactions and defense against parasitic infections. It binds to mast cells and basophils. | | Mast cells | A type of white blood cell found in connective tissues that releases histamine and other mediators of inflammation upon activation, often in response to allergens. | | Histamine | A chemical mediator released by mast cells and basophils during allergic reactions and inflammation, causing symptoms like vasodilation, increased vascular permeability, and smooth muscle contraction. | | Anaphylactic shock | A severe, life-threatening allergic reaction that occurs rapidly after exposure to an allergen, characterized by a sudden drop in blood pressure, airway constriction, and other systemic symptoms. | | Antihistamines | Medications that block the effects of histamine, thereby reducing the symptoms of allergic reactions such as itching, swelling, and sneezing. | | Immunotherapy | A medical treatment that uses the immune system to fight disease. In allergy treatment, it involves exposing the patient to small, increasing amounts of an allergen to build tolerance. | | Autoimmune reaction | An immune response that targets the body's own tissues, mistakenly identifying them as foreign. This leads to chronic inflammation and damage to organs and systems. | | Apoptosis | Programmed cell death, a controlled process that eliminates cells without causing inflammation. This is a normal physiological process and distinct from necrosis. | | Necrosis | Uncontrolled cell death resulting from injury or disease, often leading to inflammation and damage to surrounding tissues. | | Epstein-Barr Virus (EBV) | A common human herpesvirus that causes infectious mononucleosis (glandular fever) and is associated with an increased risk of certain cancers. | | Lymphoma | A type of cancer that originates in the lymphatic system, characterized by the uncontrolled proliferation of lymphocytes. |