Immunology and Rheumatology Study Notes

Objectives

• Discuss various immune-related conditions and rheumatology: Focus on conditions that are less commonly encountered in clinical settings, emphasizing the importance of knowledge in rare diseases to improve patient care.

• Engage in case studies for critical thinking: Utilize real-world examples to enhance understanding and application of immunological and rheumatological principles in diagnosis and treatment.

Key Definitions

• Immunology
  The comprehensive study of the immune system's complex network responsible for protecting the body against infections, diseases, and foreign invaders, along with understanding its role in autoimmune responses, hypersensitivity reactions, and immunodeficiencies.

• Rheumatology
  A specialized branch of medicine that focuses on diagnosing and managing inflammation-related disorders affecting not only the bones and muscles but also joints and organs. It often intersects with immune disorders, including autoimmune diseases, as these conditions can lead to systemic arthritis, myopathies, and vasculitis.

Hypersensitivity Reactions

• Definition: An exaggerated or inappropriate immune response to antigens, leading to tissue damage and clinical symptoms ranging from mild to life-threatening.

• Types of Antigens:

• Environmental Antigens: Such as pollen, dust mites, and various food proteins that trigger allergic responses.

• Self Antigens: Associated with autoimmune disorders where the immune system mistakenly targets the body's own tissues.

• Human Antigens: Varieties among individuals contributing to different immune responses, including genetic factors influencing susceptibility to diseases.

Immunoglobulin Classes

Characteristics of Immunoglobulins

• IgG:

• Structure: Monomeric form comprising two heavy and two light chains.

• Percentage: Constitutes approximately 80% of serum antibodies, reflecting its critical role in immune defense.

• Location: Predominantly found in blood and lymph; uniquely capable of crossing the placental barrier to provide passive immunity to the fetus.

• Function: Primarily responsible for neutralizing toxins and pathogens, opsonization of microbes for phagocytosis, and activating complement pathways.

• IgA:

• Structure: Exists as a dimer with a secretory component that protects it from degradation in secretions.

• Location: Found in mucosal surfaces, including the gut, respiratory tract, and also in secretions such as tears, saliva, and breast milk.

• Function: Plays a crucial role in mucosal immunity by preventing pathogen attachment and colonization at mucosal surfaces.

• IgM:

• Structure: Pentameric form, featuring five monomer units connected by a J-chain.

• Initial response antibody: The first antibody produced in response to an infection, marking current infection when detected.

• Function: Highly effective in agglutinating antigens and triggering complement activation for lysis of pathogens.

• IgD:

• Structure: Monomer, similar to IgG.

• Function: Functions primarily as an antigen receptor on B cells, playing a vital role in initiating the B cell activation and differentiation process.

• IgE:

• Structure: Monomer.

• Function: Primarily associated with allergic reactions and defense against parasitic infections; binds to mast cells and basophils, leading to histamine release upon antigen exposure.

Types of Hypersensitivity Reactions

• Type I (Immediate):

• Mechanism: Involves IgE antibodies binding to allergens, leading to rapid degranulation of mast cells and basophils, releasing histamines and other mediators.

• Examples: Allergic reactions such as hay fever, food allergies, and life-threatening anaphylaxis.

• Type II (Antibody-mediated):

• Mechanism: Involves IgG or IgM antibodies that target and destroy host cells recognized as foreign, often through complement activation or opsonization.

• Example: Blood transfusion reactions, autoimmune hemolytic anemia, and conditions like Graves’ disease.

• Type III (Immune Complex-mediated):

• Mechanism: Involves formation of immune complexes that precipitate in tissues, leading to local inflammation and tissue damage.

• Examples: Autoimmune diseases such as systemic lupus erythematosus (SLE) and rheumatoid arthritis.

• Type IV (Cell-mediated):

• Mechanism: Involves T lymphocytes and the release of cytokines, recruiting inflammatory cells to the site of exposure

• Example: Contact dermatitis, granulomatous reactions in conditions like tuberculous infections.

Anaphylaxis

• A medical emergency requiring immediate response due to life-threatening reactions.

• Symptoms: Often starts with skin reactions like hives, respiratory distress exhibiting asthma-like symptoms, gastrointestinal manifestations such as nausea and vomiting, and cardiovascular issues leading to hypotension and potential shock.

• First treatment: Administration of epinephrine is crucial; it has no absolute contraindications and should be used promptly to counteract the severe reaction.

Autoimmune Diseases

• Conditions that arise when the immune system mistakenly identifies self cells as foreign, leading to inflammatory responses and tissue damage.

• Examples of organ-specific diseases:

• Hashimoto thyroiditis: An autoimmune disorder affecting the thyroid, leading to hypothyroidism.

• Graves' disease: Causes hyperthyroidism due to autoantibodies stimulating the thyroid gland.

• Examples of systemic diseases:

• Systemic lupus erythematosus (SLE): A multifactorial disorder impacting multiple organs due to autoantibody production.

• Rheumatoid arthritis: Chronic inflammation primarily affecting joints but may also have systemic complications.

Conditions Explored

Graves Disease

• Characterized by the production of autoantibodies targeting TSH receptors, leading to unregulated production of thyroid hormones which can result in symptoms of hyperthyroidism such as weight loss, anxiety, and tremors.

Allergic Rhinitis

• Triggered by IgE-mediated reactions to environmental allergens, resulting in nasal inflammation, sneezing, and itching, significantly affecting quality of life during certain seasons or exposure periods.

Rheumatic Fever

• An inflammatory disease that can develop after an untreated streptococcal throat infection, affecting the heart, joints, skin, and brain, requiring prompt treatment to prevent severe complications.

Systemic Lupus Erythematosus

• A complex disorder characterized by a diverse array of symptoms resulting from widespread inflammation and tissue damage due to the presence of autoantibodies, often requiring long-term management and monitoring.

Chronic Fatigue Syndrome

• A debilitating condition characterized by profound fatigue lasting more than six months, post-exertional malaise, cognitive dysfunction, and unrefreshing sleep, with no identifiable cause, posing challenges for diagnosis and treatment.

Lyme Disease

• Infectious disease caused by the bacterium Borrelia burgdorferi, transmitted by tick bites; presents with erythema migrans, flu-like symptoms, and if untreated, can lead to serious neurological and cardiac complications.