Immune System Disorders
Overview
The immune system is a complex network of cells, tissues, and organs that work together to defend the body against harmful invaders such as bacteria, viruses, and other pathogens. Immune system disorders occur when the immune system does not function properly, either by overreacting, underreacting, or attacking the body's own tissues. These disorders can be broadly categorized into immunodeficiency disorders, autoimmune disorders, and hypersensitivity reactions.
Immunodeficiency Disorders
Immunodeficiency disorders are conditions where the immune system's ability to fight infectious disease is compromised or entirely absent. These disorders can be congenital (primary) or acquired (secondary).
Primary Immunodeficiency
Primary immunodeficiency disorders are typically genetic and present at birth. Examples include:
- **Severe Combined Immunodeficiency (SCID)**: Often referred to as "bubble boy disease," SCID is characterized by a severe defect in both the T- and B-lymphocyte systems. Patients with SCID are highly susceptible to infections.
- **Common Variable Immunodeficiency (CVID)**: This disorder is marked by low levels of serum immunoglobulins and an increased risk of infections. CVID can present at any age and often requires lifelong immunoglobulin replacement therapy.
Secondary Immunodeficiency
Secondary immunodeficiency disorders are acquired and can result from various factors such as infections, malnutrition, or medical treatments. Examples include:
- **Human Immunodeficiency Virus (HIV)**: HIV attacks the body's T cells, leading to acquired immunodeficiency syndrome (AIDS). This makes the body more susceptible to opportunistic infections and certain cancers.
- **Chemotherapy-Induced Immunodeficiency**: Chemotherapy drugs used to treat cancer can suppress the immune system, increasing the risk of infections.
Autoimmune Disorders
Autoimmune disorders occur when the immune system mistakenly attacks the body's own tissues. This can lead to chronic inflammation and damage to various organs and tissues.
Systemic Autoimmune Diseases
Systemic autoimmune diseases affect multiple organs and systems in the body. Examples include:
- **Systemic Lupus Erythematosus (SLE)**: SLE is a chronic autoimmune disease that can affect the skin, joints, kidneys, brain, and other organs. Symptoms vary widely and can include fatigue, joint pain, and a characteristic butterfly-shaped rash on the face.
- **Rheumatoid Arthritis (RA)**: RA is an autoimmune disorder that primarily affects the joints, causing inflammation, pain, and eventually joint destruction. It can also affect other organs such as the lungs and heart.
Organ-Specific Autoimmune Diseases
Organ-specific autoimmune diseases target specific organs or tissues. Examples include:
- **Type 1 Diabetes Mellitus**: This disorder occurs when the immune system attacks the insulin-producing beta cells in the pancreas, leading to high blood sugar levels.
- **Hashimoto's Thyroiditis**: An autoimmune disorder in which the immune system attacks the thyroid gland, leading to hypothyroidism.
Hypersensitivity Reactions
Hypersensitivity reactions are exaggerated immune responses that can cause tissue damage and disease. They are classified into four types:
Type I Hypersensitivity
Type I hypersensitivity, also known as immediate hypersensitivity, involves IgE antibodies and mast cells. Examples include:
- **Allergic Rhinitis**: Also known as hay fever, this condition is characterized by sneezing, itching, and nasal congestion in response to allergens such as pollen.
- **Anaphylaxis**: A severe, life-threatening allergic reaction that can cause difficulty breathing, low blood pressure, and shock.
Type II Hypersensitivity
Type II hypersensitivity, or cytotoxic hypersensitivity, involves IgG or IgM antibodies directed against cell surface antigens. Examples include:
- **Hemolytic Anemia**: This condition occurs when antibodies target and destroy red blood cells, leading to anemia.
- **Goodpasture's Syndrome**: An autoimmune disorder where antibodies attack the basement membrane in the lungs and kidneys, causing bleeding and kidney failure.
Type III Hypersensitivity
Type III hypersensitivity, or immune complex hypersensitivity, involves the formation of immune complexes that deposit in tissues and cause inflammation. Examples include:
- **Serum Sickness**: A reaction to foreign proteins in antiserum, characterized by fever, rash, and joint pain.
- **Systemic Lupus Erythematosus (SLE)**: As mentioned earlier, SLE can also involve type III hypersensitivity mechanisms.
Type IV Hypersensitivity
Type IV hypersensitivity, or delayed-type hypersensitivity, involves T-cell mediated immune responses. Examples include:
- **Contact Dermatitis**: An inflammatory skin condition caused by contact with allergens such as poison ivy or nickel.
- **Tuberculosis**: The immune response to Mycobacterium tuberculosis infection involves type IV hypersensitivity mechanisms, leading to granuloma formation in the lungs.
Diagnosis and Treatment
The diagnosis of immune system disorders often involves a combination of clinical evaluation, laboratory tests, and imaging studies. Treatment strategies vary depending on the specific disorder and may include:
- **Immunosuppressive Therapy**: Used to treat autoimmune diseases and prevent transplant rejection. Examples include corticosteroids, methotrexate, and biologics such as TNF inhibitors.
- **Immunoglobulin Replacement Therapy**: Used to treat primary immunodeficiency disorders by providing the necessary antibodies to fight infections.
- **Antiretroviral Therapy (ART)**: Used to manage HIV infection and prevent progression to AIDS.
- **Allergen Avoidance and Desensitization**: Strategies for managing allergic diseases, including avoidance of known allergens and immunotherapy.