An exaggerated or inappropriate immune response to a pathogen or antigen that is damaging to the host. Classified as immediate (anaphylactic), antibody dependent (cytotoxic), immune complex (Arthus), and delayed (T cell mediated).
Altered reactivity to an antigen, which can result in pathologic reactions upon subsequent exposure to that particular antigen.
Heightened responsiveness induced by allergic sensitisation. There are several types of response including that associated with allergy.
A condition in which someone reacts very strongly to something such as an allergic substance.
An exaggerated response of the immune system to a foreign substance.
Excessive sensitivity of tissues to substances or other stimuli inside or outside the body.
An excessive or abnormal reaction of the immune system to a specific stimulating or provoking agent or antigen. Hypersensitivity describes the process of interaction between a particular antigen and the body’s antibodies or lymphocytes. The degree of hypersensitivity may be based on the amount of time required for the reaction to occur, the type of antigen introduced, or organ involvement in the reaction.
An abnormal immunological reaction produced by some people when re-exposed to antigens that are innocuous to normal individuals. An antigen or allergen is a protein that stimulates an allergic response. This may result in a dramatic health- or life-threatening reaction, such as anaphylaxis, the next time the person is exposed to that antigen.
When a pathogenic organism or virus invades an organism, it may trigger an aggressive response that leads to the prompt death of affected tissue, which effectively halts the further spread of the infection (APS, BMS). This mechanism is employed by genetically susceptible plants to prevent serious damage by a specific parasite. Hypersensitivity is a specific type of sensitivity that implies a reaction to a minimal amount of inoculum. It represents the epitome of vulnerability, which is fundamentally different from immunity, even though the two terms are often conflated, such as in “the immune reaction.” However, it is crucial to avoid confusion with the animal hypersensitivity concept, which pertains to an excessive reaction caused by an antigen-antibody interaction.
The condition known as hypersensitivity is characterized by an extreme sensitivity to allergens, wherein even a minuscule quantity can elicit severe allergic responses. This state denotes a heightened reactivity to allergens, leading to pronounced allergic reactions.
Hypersensitivity is an exaggerated response of the immune system when it encounters an antigen (a foreign protein) during an infection defense. These reactions occur upon second or subsequent exposures to specific antigens after the immune system has been sensitized during the first exposure. While both hypersensitivity reactions and protective immunity share similar mechanisms, the crucial difference lies in their outcomes. Protective immunity defends against diseases, whereas hypersensitivity reactions can lead to tissue damage and disease.
Type I hypersensitivity is associated with allergies. During the first exposure to an antigen, which could be an innocuous substance like grass pollen, the immune system produces antibodies that can recognize and bind to the antigen. These antibodies coat mast cells located in different tissues. Upon subsequent exposure to the same antigen, the antigen and antibodies interact, leading to the disintegration of mast cells and the release of chemicals. These chemicals trigger symptoms such as asthma, allergic rhinitis (hay fever), urticaria (nettle rash), anaphylactic shock (a severe allergic reaction), or other allergic illnesses.
Type II reactions involve the binding of antibodies to antigens present on the surfaces of specific cells in particular tissues. This binding can potentially lead to the destruction of these cells. Type II reactions are associated with certain autoimmune disorders, where antibodies mistakenly attack the body’s own tissues. Additionally, they may be responsible for some instances of haemolysis, which is the destruction of red blood cells, triggered by certain drugs.
Type III reactions occur when antibodies combine with antigens, forming immune complexes that can lodge in different tissues. This triggers additional responses from the immune system, leading to tissue damage. These reactions are responsible for conditions like serum sickness, allergic alveolitis (a lung disease caused by exposure to certain fungi spores), and the development of large swellings that may occur after a person receives a booster vaccination.
Type IV reactions involve sensitized T-lymphocytes, a type of white blood cell, binding to antigens and releasing lymphokines, which trigger an inflammatory response. These reactions are responsible for conditions like contact dermatitis and the rash seen in measles. Additionally, they may play a role in certain “allergic” reactions to drugs.
The treatment for hypersensitivity varies based on the type, cause, and severity of the reaction. Whenever feasible, it is essential to avoid exposure to the triggering antigen responsible for the hypersensitive response.