Hypersensitivity (also known as hypersensitivity response or intolerance) is a term used to describe undesirable reactions that are caused by the immune system, which includes autoimmunity and allergies. These are typically called an overreaction of the immune system, and these reactions can be harmful and uncomfortable. It is an immunologic term , and should not be misinterpreted as a psychiatric term of being hypersensitive, which refers that a person is hypersensitive to physical (ie sounds, touch light, sound, etc.) or emotional stimuli. However, there is a link between the two , studies have demonstrated that with ADHD (a mental disorders) tend to experience hypersensitivity reactions, such as asthma, allergies, or eczema and more than people who don’t have ADHD.
Different kinds of hypersensitivity reactions
The hypersensitivity reaction can be divided into 4 different types.
Type II: The antibody-mediated Cytotoxic Reaction (IgG or IgM antibodies)
Type III: Complex-mediated immune immune reaction
Type IV: cell-mediated delayed hypersensitivity reaction that is delayed
The three first types are considered to be immediate hypersensitivity reactions since they happen after 24 hours. The fourth kind is known as delayed hypersensitivity reactions because it typically occurs for longer than 12 hours after being exposed to an allergen with the maximum time of reaction of between 72 and 48 hours.
Alternative Name
Type I
Type II
Type III
Type IV
Hypersensitivity to allergens
Hypersensitivity to cytotoxic chemicals
Complex hypersensitivity to immune system
Hypersensitivity caused by cells/ delayed kind of hypersensitivity
Principle
Type I
Type II
Type III
Type IV
Antibody-mediated degranulation and granulocyte degranulation leading to the death of cells.
The destruction by antibodies of cells that are healthy.
Complex-mediated destruction of cells by antigens.
T lymphocytes are responsible for elimination of the cells.
Primary Mediator
Type I
Type II
Type III
Type IV
IgE
IgG/IgM
IgG/IgM
Certain subsets of helper CD4+ T cells or T cells that are CD8+.
Other components that act as mediators
Type I
Type II
Type III
Type IV
Mast cell, Basophils and histamine, among other drugs
Allergen-specific IgE antibodies attach to mast cells through the Fc receptor. When the allergen of interest is bound to the IgE and cross-links with IgE results in the disgranulation in mast cells.
IgG and IgM antibody can bind to a cell-specific antigen which triggers complement activation and cell destruction. IgG can also play a role in ADCC by macrophages, natural killer cells and neutrophils.
Antigen-antibody complexes accumulate in tissues. Complement activation releases inflammation mediators and also recruits neutrophils. Inflammatory enzymes released by neutrophils harm tissues.
Th2 cells release cytokines that activate macrophages as well as T cells that are cytotoxic.
