Immune system disorders occur when the body's immune system does not function properly. The immune system is a complex network of cells, proteins, tissues, and organs that work together to fight off harmful substances and disease-causing microorganisms called pathogens. A healthy immune system helps protect the body from disease, infection, and cancer.
An immune system disorder can be classified as either an autoimmune disorder or an immune deficiency.
Autoimmune disorders occur when the immune system mistakes body cells for harmful invaders, such as bacteria, and attacks them. Autoimmune disorders can destroy body tissues, cause abnormal organ growth, and/or impair organ function.
Immune deficiencies occur when an individual's ability to fight against an infectious disease is compromised or entirely absent. Patients who suffer from immune deficiencies experience recurrent infections, such as sinusitis and pneumonia. There are two main types of immune deficiencies: primary immune deficiencies and secondary immune deficiencies.
Primary immune deficiencies are disorders that occur because part of the body's immune system does not function properly. These disorders are caused by intrinsic or genetic defects in the immune system. Some primary immune deficiencies are inherited, which means they are passed down through family members. Individuals who have primary immune deficiencies are born with the disorders.
The World Health Organization (WHO) has identified nearly 100 primary immune deficiency diseases, including X-linked agammaglobulinemia (Bruton's Disease), common variable immune deficiency (CVID), and selective immunoglobulin A deficiency.
Many individuals affected by primary immune deficiency diseases require life-long therapies, such as intravenous immune globulin infusions, antibiotic therapies, or bone marrow transplantations.
Secondary immune deficiencies are caused by factors outside of the body, such as chemotherapy treatment, radiation therapy, malnutrition, HIV infection, and diabetes. In addition, diseases, such as leukemia and multiple myeloma, cause cancerous immune cells to infiltrate the bone marrow, which is responsible for producing immune system cells. Secondary immune deficiency also occurs among critically ill patients and the elderly.
Secondary immune deficiencies usually resolve once the underlying illness is treated or the outside factor is eliminated. For instance, immune deficiencies caused by chemotherapy or radiation therapy generally resolve once the treatment is completed.
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