Hypersensitivity, Overview of the 4 Types, Animation.

Summary

Hypersensitivity involves the immune system's abnormal reactions to antigens, encompassing allergies and autoimmune diseases. It can cause mild to severe symptoms, including anaphylactic shock. Factors include immune system imbalance and self-reactivity of immune cells. Hypersensitivity is categorized into four types, with type I being common allergies, type II linked to autoimmune conditions, type III causing inflammation through immune complexes, and type IV involving T-cell mediated delayed reactions like contact dermatitis.

Takeaways

• 🚨 Hypersensitivity is an abnormal immune response to antigens, including allergies and autoimmune diseases.
• 🌡 Reactions can vary from mild symptoms like rashes to severe conditions such as anaphylactic shock.
• 🔁 Two main factors contribute to hypersensitivity: imbalance in immune response regulation and self-reactivity of immune cells.
• 🛡️ Hypersensitivity only occurs in pre-sensitized individuals who have had previous contact with an antigen.
• 🏥 Type I hypersensitivity involves IgE antibodies and can lead to immediate allergic reactions like edema and bronchospasm.
• 🩸 Type II hypersensitivity is characterized by antibodies binding to the body's own cells, causing cell destruction or dysfunction.
• 🔍 Type III hypersensitivity involves antibody-antigen complexes that trigger inflammation and tissue damage, such as in serum sickness.
• 🛑 Type IV hypersensitivity is a delayed reaction mediated by T-cells, causing conditions like contact dermatitis and positive tuberculosis skin tests.
• 🛡️ IgE antibodies in type I hypersensitivity bind to mast cells and basophils, leading to the release of histamine and other chemicals upon re-exposure.
• 🔄 In type II, antibodies can mark cells for destruction by the immune system or interfere with their normal functions.
• 🔗 Type III hypersensitivity can result from the deposition of immune complexes in blood vessel walls, causing inflammation or vasculitis.
• 🌐 T-cells in type IV hypersensitivity release inflammatory cytokines or induce cytotoxic reactions upon re-exposure to an antigen.

Q & A

What is hypersensitivity and what types of reactions does it include?

Hypersensitivity is an abnormal reaction of the immune system against certain antigens. It includes exaggerated reactions to harmless environmental antigens known as allergies, and inappropriate reactions against the body's own antigens, which are autoimmune diseases.

What are the two principal groups of factors contributing to hypersensitivity?

The two principal groups of factors contributing to hypersensitivity are the imbalance between effectors and regulators of immune response, and the self-reactivity of immune cells.

How do self-reactive immune cells develop and why do they pose a problem?

Self-reactive T-cells and B-cells develop in the thymus and bone marrow, learning not to react to the body's own antigens. Normally, these cells are eliminated, but in some cases, they escape and may attack the body's own tissues once activated.

Why do hypersensitivity reactions only occur in pre-sensitized individuals?

Hypersensitivity reactions only occur in pre-sensitized individuals because the body must have had previous contact with the antigen, which led to the production of antibodies or activation of immune cells that may cause symptoms upon subsequent exposures.

What are the four types of hypersensitivity reactions based on mechanisms of action?

The four types of hypersensitivity reactions are Type I, involving IgE antibodies and mast cells; Type II, involving IgG or IgM antibodies binding to cell surfaces; Type III, involving antibody-antigen complexes and complement activation; and Type IV, a delayed T-cell mediated reaction.

What is the role of IgE in Type I hypersensitivity reactions?

In Type I hypersensitivity, IgE antibodies bind to receptors on the surface of mast cells and basophils. Upon re-exposure to the antigen, a signaling cascade is triggered, leading to the release of histamine and other inflammatory chemicals.

What are the symptoms of a severe Type I hypersensitivity reaction?

Severe Type I hypersensitivity reactions can lead to anaphylactic shock, a life-threatening condition characterized by a drop in blood pressure and narrowing of the airways.

How does Type II hypersensitivity differ from Type I, and what are its implications?

Type II hypersensitivity involves IgG or IgM antibodies binding to antigens on the surface of cells, marking them for destruction. This type is the basis of many autoimmune diseases where the body produces antibodies to destroy its own cells.

What is the mechanism behind Type III hypersensitivity reactions, and what is a typical example?

Type III hypersensitivity is mediated by IgM or IgG antibodies binding to free-floating antigens, forming complexes that activate the complement system and cause inflammation. An example is serum sickness, induced by a large amount of antigens in the blood.

How does Type IV hypersensitivity differ from the other types, and what are some examples?

Type IV hypersensitivity is a delayed reaction mediated by T-cells. It involves pre-sensitized T-cells releasing inflammatory cytokines or inducing cytotoxic reactions. Examples include contact dermatitis and the tuberculosis skin test.