Immune mediated reactions, also known as hypersensitivity reactions, are the different ways the immune system can respond in an exaggerated or inappropriate manner. Based on the mechanism and timing, these reactions are typically classified into four main types.
These reactions occur when the immune system, in trying to protect the body, causes damage to its own tissues. The type of reaction depends on the specific components of the immune system involved and the timing of the response.
The Four Types of Immune Mediated Reactions
Immune mediated reactions are categorized into four distinct types based on the immunological mechanisms driving them. Each type is characterized by the primary mediator involved in the reaction.
Type I: Immediate Hypersensitivity
This type of reaction is mediated by IgE antibodies. It is often rapid and occurs minutes after exposure to an antigen.
Type II: Cytotoxic Hypersensitivity
Type II reactions are cytotoxic reactions mediated by IgG or IgM antibodies. These antibodies target antigens on the surface of cells or tissues, leading to damage or destruction of those cells.
Type III: Immune Complex Hypersensitivity
This reaction is mediated by immune complexes. These complexes are formed when antibodies bind to soluble antigens. If these complexes are not cleared effectively, they can deposit in various tissues, triggering inflammation and tissue damage.
Type IV: Delayed Hypersensitivity
Unlike the other types which are antibody-mediated, Type IV reactions are delayed reactions mediated by cellular response. This involves T lymphocytes, specifically effector T helper cells and cytotoxic T cells, rather than antibodies. The reaction typically takes 24 to 72 hours to develop after antigen exposure.
Summary of Immune Mediated Reaction Types
Here is a summary of the four types based on their mediators:
| Type | Mediator(s) | Common Name |
|---|---|---|
| Type I | IgE antibodies | Immediate Hypersensitivity |
| Type II | IgG or IgM antibodies | Cytotoxic Hypersensitivity |
| Type III | Immune complexes | Immune Complex Hypersensitivity |
| Type IV | Cellular response (T cells) | Delayed Hypersensitivity |
Understanding these types is crucial in diagnosing and managing various allergic, autoimmune, and inflammatory conditions.
