Immunological diseases refer to the conditions in which the immune system fails to function properly, leading to various health issues. These diseases can be classified into two broad categories: hypersensitivity reactions and immunodeficiency disorders.
Hypersensitivity reactions are an overactive immune response to certain substances, such as food, pollen, or drugs, which can cause various symptoms, ranging from mild to life-threatening. There are four types of hypersensitivity reactions:
- Type I: Immediate or anaphylactic hypersensitivity, which is triggered by the release of histamine from mast cells and basophils. Symptoms include hives, itching, swelling, and anaphylactic shock.
- Type II: Antibody-mediated cytotoxic hypersensitivity, which involves the destruction of cells by antibodies directed against them. Examples include autoimmune hemolytic anemia and drug-induced hemolytic anemia.
- Type III: Immune complex-mediated hypersensitivity, which occurs when antigen-antibody complexes accumulate in tissues and trigger inflammation. Examples include systemic lupus erythematosus and rheumatoid arthritis.
- Type IV: Cell-mediated or delayed hypersensitivity, which is mediated by T cells and causes tissue damage. Examples include contact dermatitis and tuberculin reactions.
Immunodeficiency disorders, on the other hand, are caused by defects in the immune system, which can result in increased susceptibility to infections and other diseases. Immunodeficiency disorders can be primary (genetic) or acquired (secondary to other factors, such as infections, drugs, or chemotherapy). Examples of immunodeficiency disorders include:
- Severe combined immunodeficiency (SCID), a rare genetic disorder that causes a complete lack of immune function.
- Common variable immunodeficiency (CVID), a genetic disorder that leads to a decreased ability to produce antibodies.
- Acquired immunodeficiency syndrome (AIDS), a viral infection caused by the human immunodeficiency virus (HIV), which attacks and destroys the immune system.
- X-linked agammaglobulinemia (XLA), a genetic disorder that affects the development of B cells, leading to a lack of antibody production.
- Chronic granulomatous disease (CGD), a genetic disorder that affects the ability of white blood cells to kill certain bacteria and fungi.
