13.2 Allergic responses and IgE-mediated immunity

IgE, or Immunoglobulin E, is a type of antibody that plays a critical role in the immune system, especially in allergic reactions and responses to parasitic infections. It is produced in response to allergens and binds to mast cells and basophils, leading to the release of histamine and other mediators that cause allergy symptoms. This antibody type is unique as it is primarily involved in immediate hypersensitivity reactions, distinguishing it from other immunoglobulin classes.

Allergen: A substance that can cause an allergic reaction by triggering the immune system to produce IgE antibodies.

Mast Cells: Immune cells that contain histamine and other chemicals; they play a key role in allergic responses by releasing these mediators when bound by IgE.

Affinity Maturation: The process through which B cells increase the affinity of antibodies for their specific antigens, which can also include IgE during immune responses.

Mast cells are a type of white blood cell that plays a crucial role in the immune system, particularly in allergic reactions and defense against parasites. They are found in various tissues, especially in the skin, lungs, and digestive tract, where they release histamine and other chemicals that contribute to inflammation and immune responses.

Histamine: A chemical released by mast cells during an immune response that causes blood vessels to dilate and contributes to inflammation and allergy symptoms.

IgE: Immunoglobulin E (IgE) is an antibody produced by the immune system that binds to allergens and triggers mast cell activation, leading to allergic reactions.

Anaphylaxis: A severe, life-threatening allergic reaction characterized by rapid onset of symptoms, including difficulty breathing, swelling, and a drop in blood pressure, often involving mast cell degranulation.

Basophils are a type of white blood cell that plays a crucial role in the immune response, particularly in allergic reactions and inflammation. These cells are characterized by their large granules filled with histamine and other chemicals that are released during immune responses. Basophils are derived from hematopoietic stem cells in the bone marrow and are part of the innate immune system, making them essential in mediating hypersensitivity reactions and contributing to the body's defense mechanisms.

Mast Cells: Mast cells are immune cells similar to basophils, found in tissues rather than circulating in the blood, that release histamine and play a key role in allergic responses.

Histamine: Histamine is a chemical released by basophils and mast cells during allergic reactions that contributes to inflammation and symptoms like itching, swelling, and bronchoconstriction.

IgE Antibodies: IgE antibodies are a class of immunoglobulins that bind to allergens and trigger basophils and mast cells to release histamine, initiating an allergic response.

Leukotrienes are lipid compounds that are produced by immune cells and play a critical role in inflammatory responses, particularly in the context of allergic reactions and asthma. These mediators are derived from arachidonic acid and function by promoting bronchoconstriction, increasing vascular permeability, and attracting immune cells to sites of inflammation, thus influencing both innate immunity and allergic responses.

Arachidonic Acid: A polyunsaturated fatty acid that is a key component of cell membrane phospholipids, serving as a precursor for the synthesis of leukotrienes and other eicosanoids.

Mast Cells: A type of immune cell that plays a crucial role in allergic reactions, releasing histamine and leukotrienes upon activation.

Cysteinyl Leukotrienes: A subgroup of leukotrienes, including LTC4, LTD4, and LTE4, that are particularly potent in inducing bronchoconstriction and promoting inflammation in asthma.

Anaphylaxis is a severe, potentially life-threatening allergic reaction that occurs rapidly after exposure to an allergen. It involves a sudden release of mediators from mast cells and basophils, primarily driven by immunoglobulin E (IgE) antibodies. Understanding anaphylaxis is crucial as it represents a critical form of hypersensitivity reaction and requires immediate medical intervention.

Allergen: A substance that can cause an allergic reaction, such as food proteins, insect venom, or certain medications.

Epinephrine: A hormone and neurotransmitter used as a first-line treatment for anaphylaxis, which helps to reverse the symptoms by constricting blood vessels and relaxing airway muscles.

Mast Cells: A type of white blood cell that plays a key role in allergic responses by releasing histamines and other inflammatory mediators during an allergic reaction.

An allergen is a substance that triggers an allergic reaction in sensitive individuals, often leading to an immune response characterized by the production of specific antibodies, particularly Immunoglobulin E (IgE). Allergens can be found in various forms, such as proteins, pollen, dust mites, certain foods, and insect venom, and they play a central role in hypersensitivity reactions that can vary in severity from mild to life-threatening.

IgE: Immunoglobulin E (IgE) is a type of antibody produced by the immune system in response to allergens and is primarily involved in allergic reactions and protection against parasitic infections.

hypersensitivity: Hypersensitivity refers to an exaggerated immune response to a harmless substance, which can lead to tissue damage and various clinical symptoms.

anaphylaxis: Anaphylaxis is a severe, potentially life-threatening allergic reaction that occurs rapidly after exposure to an allergen, characterized by symptoms such as difficulty breathing, swelling, and shock.

Cross-linking of IgE refers to the process where two or more IgE antibodies bind simultaneously to the same allergen, leading to the aggregation of IgE on the surface of mast cells and basophils. This aggregation is crucial for the activation of these immune cells, resulting in the release of inflammatory mediators such as histamine, which contribute to allergic reactions.

Mast Cells: Mast cells are a type of immune cell found in connective tissues that play a significant role in allergic responses by releasing histamine and other mediators upon activation.

Allergen: An allergen is any substance that can provoke an allergic reaction, often triggering the production of IgE antibodies in sensitized individuals.

Histamine: Histamine is a chemical released by mast cells during an allergic reaction, responsible for symptoms such as itching, swelling, and bronchoconstriction.

Degranulation is the process by which immune cells, particularly mast cells and basophils, release their pre-stored granules containing various biologically active substances, including histamines and cytokines. This process plays a crucial role in the body's immediate response to pathogens and allergens, leading to inflammation and recruitment of other immune cells to the site of infection or injury. Degranulation is central to both innate immunity and allergic responses, highlighting its importance in various hypersensitivity reactions.

Mast Cells: A type of immune cell that is involved in allergic reactions and the defense against pathogens, known for storing and releasing histamines during degranulation.

Histamine: A chemical released during degranulation that plays a key role in inflammatory responses, causing blood vessel dilation and increased permeability.

Cytokines: Signaling proteins released by immune cells during degranulation that help regulate immunity, inflammation, and hematopoiesis.

Prostaglandins are lipid compounds that have hormone-like effects in various tissues throughout the body. They are derived from fatty acids and play a crucial role in mediating inflammation, regulating immune responses, and facilitating communication between cells. Their production is often triggered by injury or infection, linking them directly to the body's response mechanisms and influencing both acute and chronic inflammatory processes.

Cytokines: Signaling proteins produced by immune cells that mediate and regulate immunity, inflammation, and hematopoiesis.

Eicosanoids: A class of bioactive lipids derived from arachidonic acid, which includes prostaglandins, thromboxanes, and leukotrienes, playing key roles in inflammation and immune responses.

Histamine: A biogenic amine involved in local immune responses, functioning as a neurotransmitter, and playing a significant role in allergic reactions.

Hay fever, also known as allergic rhinitis, is an allergic reaction characterized by symptoms such as sneezing, runny nose, itchy eyes, and congestion, triggered by airborne allergens like pollen. This condition occurs when the immune system mistakenly identifies these harmless substances as threats, leading to an overreaction that results in inflammation and discomfort.

Allergen: A substance that can provoke an allergic reaction in susceptible individuals, such as pollen, mold spores, pet dander, or certain foods.

IgE Antibodies: Immunoglobulin E (IgE) antibodies are a type of antibody produced by the immune system in response to allergens and play a crucial role in mediating allergic reactions.

Histamine: A chemical released by mast cells during an allergic reaction that contributes to inflammation and symptoms like itching, swelling, and mucus production.

Asthma is a chronic inflammatory disease of the airways characterized by episodes of wheezing, shortness of breath, chest tightness, and coughing. It is often triggered by allergens, irritants, and environmental factors, leading to airway hyperreactivity and obstruction. Understanding asthma involves recognizing its connection to allergic responses and the role of IgE-mediated immunity in exacerbating symptoms.

IgE: Immunoglobulin E (IgE) is a type of antibody that plays a critical role in allergic reactions and asthma by binding to allergens and triggering inflammatory responses.

bronchoconstriction: Bronchoconstriction refers to the tightening of the muscles around the airways, leading to narrowing and difficulty in breathing, often experienced during an asthma attack.

allergens: Allergens are substances that can cause an allergic reaction, such as pollen, dust mites, mold, and pet dander, which can trigger asthma symptoms in sensitive individuals.

Eczema, also known as atopic dermatitis, is a chronic inflammatory skin condition characterized by red, itchy, and dry patches on the skin. It is commonly associated with allergic responses and is often linked to an imbalance in the immune system, particularly involving IgE-mediated immunity, where the body reacts abnormally to allergens, resulting in inflammation and skin barrier dysfunction.

IgE: Immunoglobulin E (IgE) is a type of antibody that plays a crucial role in allergic reactions and defenses against parasitic infections.

Allergen: An allergen is a substance that can cause an allergic reaction by triggering the immune system to respond, leading to symptoms like those seen in eczema.

Skin Barrier Dysfunction: Skin barrier dysfunction refers to the impaired ability of the skin to act as a protective barrier, which can lead to increased water loss and susceptibility to allergens and irritants.