Type I Hypersensitivity and Allergic Reactions

A substance that triggers an allergic reaction in the body upon re-exposure. Examples include pollen, certain foods, bee venom, and penicillin.

The reaction occurs within minutes of re-exposure to the allergen.

Antigen-presenting cells digest the allergen and present it to T helper 2 cells (TH2 cells).

TH2 cells release Interleukins 4, 5, and 13, which activate B cells to produce IgE antibodies.

IgE antibodies attach to mast cells and basophils. This makes the individual sensitized.

The allergen binds to IgE antibodies on mast cells, cross-linking them and causing degranulation.

The mediators released from degranulation include histamine, leukotrienes, heparin, prostaglandins, and platelet-activating factor (PAF).

These mediators cause smooth muscle contractions, vasodilation, increased vascular permeability, increased mucus secretion, and stimulation of nerve endings, leading to symptoms like itching and pain.

A type of hypersensitivity reaction characterized by a rapid and excessive immune response to an allergen. It involves the activation of mast cells and basophils, leading to the release of histamine and other inflammatory mediators.

Specialized cells that release histamine and other inflammatory mediators, leading to the symptoms of Type I hypersensitivity reactions.

A severe, life-threatening allergic reaction that involves widespread vasodilation, bronchospasm, and a drop in blood pressure.

A localized allergic reaction that typically involves specific tissues and organs.

A diagnostic test used to identify specific allergens that trigger allergic reactions.

A process where a substance (allergen) binds to IgE antibodies attached to mast cells, triggering their degranulation and the release of histamine and other inflammatory mediators.

A medical condition characterized by recurrent episodes of wheezing, shortness of breath, chest tightness, and coughing, often triggered by allergens.

A condition characterized by inflammation and swelling of the nasal passages, often triggered by allergens.

A small, round, inflamed area that appears after skin contact with an allergen.

A type I hypersensitivity reaction involving IgE antibodies, mast cells, histamine release, and localized inflammation.

A test that measures the level of IgE antibodies in the blood, which can indicate an allergic tendency.

A test that measures the level of IgE antibodies specific to a particular allergen.

Avoiding contact with an allergen is the best way to prevent an allergic reaction.

A treatment involving repeated small doses of an allergen to build tolerance and reduce allergic reactions.

A type of hypersensitivity reaction involving antibodies (IgM or IgG) reacting with antigens on cell surfaces, leading to cell destruction.

Antibodies act like 'tags' that signal immune cells to engulf and destroy target cells, contributing to tissue damage in type II hypersensitivity.

Antibodies bind to Fc receptors on immune cells like NK cells, macrophages, or neutrophils, triggering the release of cytotoxic molecules like perforins and granzymes, leading to target cell destruction.

A component of the complement system that coats microbes, making them more attractive for phagocytosis by immune cells.

A complex of complement proteins that forms pores in cellular membranes, leading to cell lysis and death.

Antibodies that bind to specific receptors on cells can disrupt normal function, leading to diseases like Graves' disease (thyroid stimulating hormone receptor) or myasthenia gravis (acetylcholine receptor).

The process of red blood cell destruction due to immune system incompatibility, often triggered by blood transfusions or during pregnancy.

ABO antigens on red blood cells are unique to each individual, causing reactions if mismatched blood types are transfused.

When a Rh-negative mother carries a Rh-positive fetus, maternal antibodies are activated, potentially causing hemolysis of fetal red blood cells.

A test used to detect antibodies bound to red blood cells, often used to diagnose alloimmune hemolysis.

A type of autoimmune reaction where antibodies attack the patient's own red blood cells, platelets, or granulocytes, leading to their destruction. This can occur as a part of an autoimmune disease or be triggered by drugs.

Antibodies mistakenly attack antigens on cells, leading to cell destruction. The antibodies can be against red blood cells, platelets, or granulocytes.

Immune complexes (antigen-antibody-complement) are formed and deposited in tissues, causing inflammation and damage. The antigen can be exogenous (from outside the body) or endogenous (from within the body).

IgG antibodies are the primary type involved in Type III hypersensitivity.

Immune complexes are normally removed by phagocytes but can accumulate in certain conditions, leading to their deposition in tissues, often in the skin, joints, and kidneys.

Inflammation in blood vessel walls is triggered by complement activation and leukocyte attachment to immune complexes, leading to tissue damage. Platelet aggregation and micro-thrombi formation further contribute to damage.

Inflammation, immunosuppression, and symptomatic treatment are used to manage autoimmune conditions like those involving Type III hypersensitivity.

ELISA and immunofluorescence are used to detect circulating antibodies and complement in the lesions to diagnose Type III hypersensitivity.

An immune response characterized by the formation of immune complexes that deposit in tissues, leading to inflammation and tissue damage.

A condition caused by the deposition of immune complexes in small arteries, mainly in the skin, kidneys, and joints, leading to vasculitis, nephritis, and arthritis.

A localized reaction that occurs after repeated subcutaneous injections of an antigen, leading to the formation of immune complexes at the injection site and resulting in local vasculitis and necrosis.

A hypersensitivity pneumonitis caused by the deposition of immune complexes in the lungs after repeated inhalation of mold spores or pigeon feces.

A type of hypersensitivity reaction that involves the interaction of T cells and macrophages, without the participation of antibodies.

The key cell type involved in Type IV hypersensitivity reactions, responsible for recognizing antigen in a complex with MHC II and secreting cytokines that activate other immune cells.

Cells that engulf and process antigens, presenting them to T cells in the context of MHC II, and releasing cytokines that contribute to the inflammatory response in Type IV hypersensitivity.

A type of immune response that involves the activation of T cells and macrophages, usually leading to chronic inflammation and tissue damage. Common examples include contact dermatitis, tuberculosis, and graft rejection.