Question

Inflammatory molecules are released by mast cells in type I hypersensitivities; type II hypersensitivities, however, are characterized by which of the following? a. cell lysis (cytotoxicity) b. strong antibody reactions against antigens c. leukotriene release upon stimulation d. localized tissue reactions, such as hives

Short answer

Type II hypersensitivities are characterized by cell lysis (cytotoxicity), so the correct answer is (a).

Step-by-step solution

Understanding Hypersensitivity Reactions

Type I hypersensitivities involve IgE antibodies that cause an allergic reaction, primarily involving the release of inflammatory molecules like histamine from mast cells. It's important to note that this is not the characteristic of type II hypersensitivities.

Identifying Characteristics of Type II Hypersensitivities

Type II hypersensitivities involve IgG and IgM antibodies that mediate cytotoxic reactions by binding to antigens on the surface of cells, targeting them for destruction. These reactions can cause cell lysis and are linked to autoimmune conditions like hemolytic anemia or Rh disease during pregnancy.

Eliminating Incorrect Options

Options b, c, and d are more characteristic of other types of hypersensitivities or different immune responses. Option b is a general feature of many hypersensitivities; option c is associated with leukotriene release, which relates to type I hypersensitivity; and option d, which mentions localized reactions such as hives, also relates to type I hypersensitivity not type II.

Key concepts

IgG and IgM Mediated Cytotoxicity

When discussing type II hypersensitivity reactions, we are primarily considering the roles of the immunoglobulins: IgG and IgM. These are specific types of antibodies produced by the immune system in response to the presence of certain antigens on the surface of cells. Unlike the IgE mediated response that results in the immediate allergic reactions of type I hypersensitivity, IgG and IgM antibodies lead to a cytotoxic response.

This mechanism starts when IgG or IgM antibodies bind to antigens on the surface of target cells. This action flags the cells as targets to various immune cells such as natural killer cells, macrophages, or components of the complement system, which can then lead to the destruction of the target cells—a process known as cell lysis. This cytotoxicity is a particular characteristic of type II hypersensitivity and can result in widespread tissue damage and disease if not properly regulated.

Examples of IgG/IgM Mediated Diseases

• Hemolytic anemia: Red blood cells are targeted and destroyed.
• Rh disease: Occurs when the blood types of a pregnant mother and her baby are incompatible.
• Some forms of thrombocytopenia: Platelets are targeted for destruction.

These examples highlight the critical role IgG and IgM play within the immune system and the delicate balance required to protect the body without causing harm to itself.

Autoimmune Conditions

Autoimmune conditions represent a situation where the body's immune system mistakenly targets and attacks the body's own cells, tissues, or organs. In the context of type II hypersensitivity, the issue arises when the IgG or IgM antibodies directed against foreign pathogens erroneously recognize self antigens, treating them as if they were foreign.

This autoimmune attack can lead to a myriad of debilitating diseases, depending on which tissues or cells are being attacked. Autoimmune conditions can affect any part of the body, and because they result from a dysfunction within the immune system itself, treatment often involves suppressing immune activity to mitigate damage.

Common Autoimmune Diseases related to Type II Hypersensitivity

• Graves' disease: The immune system targets the thyroid gland, leading to overproduction of thyroid hormones.
• Myasthenia gravis: Antibodies attack nerve receptors, causing muscle weakness.
• Goodpasture's syndrome: The immune system attacks the kidneys and lungs.

Understanding the underlying cause and managing autoimmune conditions is crucial for patient health and quality of life.

Immune Response in Hypersensitivities

In hypersensitivity reactions, the body's immune response is exaggerated and can cause damage to the body's own tissues. Type II hypersensitivities are characterized by antibody-mediated immune responses, where the response is not to a pathogen, but rather to self or altered-self cells.

The antibodies mainly involved, IgG and IgM, cause destruction through various pathways. One pathway is by activating the complement system, a series of proteins that promote inflammation, opsonization, and cell lysis. Another pathway is antibody-dependent cellular cytotoxicity (ADCC), where immune cells with Fc receptors recognize the antibody-coated cells and destroy them.

Managing immune responses in hypersensitivities often involves understanding the specific triggers and mechanisms involved in the exaggerated response. This understanding can lead to therapies that specifically target the problematic immune components while preserving as much of the normal immune function as possible, thereby reducing tissue damage and alleviating the condition.