Hypersensitivity refers to an exaggerated or inappropriate response of the immune system to external or internal stimuli. There are different types of hypersensitivity, each with its own specific characteristics. In this article, we will explore the 4 types of hypersensitivity, their underlying mechanisms and associated clinical manifestations.
Type I: Immediate or allergic hypersensitivity
Type I hypersensitivity, also known as immediate or allergic hypersensitivity, is an exaggerated reaction of the immune system to exposure to certain substances, called allergens. This reaction triggers the release of inflammatory mediators such as histamine, resulting in symptoms ranging from mild to life-threatening within minutes. The process begins with sensitization, where the immune system produces specific antibodies (IgE) against the allergen after a first contact.
Characteristics of type I hypersensitivity:
- Quick response: Symptoms usually appear within minutes after exposure to the allergen.
- Inflammatory mediators: Mediators such as histamine are released, causing inflammation. characteristic allergy symptoms.
- Various symptoms: They may include itching, skin rashes, difficulty breathing, swelling and in severe cases, anaphylaxis.
Common triggers for type I hypersensitivity include foods such as peanuts, pollen, dust mites, insect bites, medications, and latex. The diagnosis is based on clinical history, allergy skin tests, and determination of specific IgE for the allergen involved. Treatment includes avoidance of the allergen, medications to relieve symptoms, and in severe cases, the administration of epinephrine in situations of anaphylaxis.
Type II: Cytotoxic hypersensitivity
Type II hypersensitivity It involves the destruction of the body's own cells by the immune system, generally due to the presence of autoantibodies. These antibodies can be directed against antigens present on the cell surface or against extracellular antigens released by damaged tissues. The consequence is tissue damage and organ dysfunction.
Characteristics of type II hypersensitivity:
- Cell destruction: Autoantibodies bind to cells , activating destruction mediated by cytotoxic cells or by activating the complement system.
- Varied clinical manifestations: They can include hemolytic anemia, autoimmune diseases such as systemic lupus erythematosus and some forms of thyroiditis.
- Variable response time: Symptoms can manifest acutely or chronically, depending on the type of antibodies and cells involved.
Some examples of type II hypersensitivity include hemolytic disease of the newborn, where the mother produces antibodies against red blood cells of the fetus, and idiopathic thrombocytopenic purpura, where platelets are destroyed by autoantibodies. Diagnosis is based on laboratory tests to detect autoantibodies and markers of cell destruction. Treatment may include immunosuppressive therapies and in some cases, the removal of the affected organ.
Type III: Hypersensitivity due to immune complexes
Type III hypersensitivity involves the formation of immune complexes between antigens and antibodies, which are deposited in tissues and trigger a localized inflammatory response. These immune complexes can cause direct tissue damage or activate the complement system, triggering an inflammatory response mediated by neutrophils and macrophages.
Characteristics of type III hypersensitivity:
- Immune complex deposition: Antigens and antibodies form complexes that are deposited in tissues, triggering localized inflammation.
- Inflammatory response: Immune system cells are activated in the site of deposition, causing tissue damage and clinical manifestations.
- Systemic manifestations: They can involve multiple organs and tissues, manifesting as vasculitis, glomerulonephritis and arthritis.
Examples of diseases associated with type III hypersensitivity include rheumatoid arthritis, IgA vasculitis, and post-streptococcal glomerulonephritis. Diagnosis is made through laboratory tests to detect levels of immune complexes and markers of inflammation. Treatment may include anti-inflammatory drugs, therapies aimed at controlling the immune response, and in severe cases, immunosuppression.
Type IV: Delayed or cellular hypersensitivity
Type IV hypersensitivity, also Known as delayed or cellular hypersensitivity, it is characterized by an immune response mediated by T lymphocytes and macrophages. Unlike the other types of hypersensitivity, type IV does not involve the participation of antibodies, but rather a cellular response directed against specific antigens present in cells or tissues.
Characteristics of type IV hypersensitivity:
- Cell-mediated response: Activated T lymphocytes generate an inflammatory response that recruits macrophages and other leukocytes to the site of injury.
- Gradual development of symptoms: Symptoms usually appear within hours to days after exposure to the antigen, due to the recruitment and activation of immune cells. Varied manifestations: strong> They include contact dermatitis, delayed reactions to tuberculin and autoimmune diseases such as type 1 diabetes.
Type IV hypersensitivity is divided into two subtypes: type IVa, mediated by CD4+ T lymphocytes (TH1 type response), and type IVb, mediated by CD8+ T lymphocytes. Clinical examples include tuberculin reaction in tuberculosis, chemical contact dermatitis, and celiac disease. Diagnosis is based on skin allergy testing and evaluation of the response to specific antigens. Treatment may involve elimination of the triggering agent, therapies to control inflammation, and in some cases, immunosuppression.
In conclusion, the 4 types of hypersensitivity present different immunological mechanisms and diverse clinical manifestations. Understanding these differences is essential for accurate diagnosis and appropriate treatment. Identification of specific triggers and modulation of the immune response are key aspects in the management of hypersensitivity disorders. An interdisciplinary approach that includes health professionals such as allergists, immunologists and dermatologists is essential to offer comprehensive care to patients with hypersensitivity.