Autoimmunity

Autoimmune diseases: These are diseases characterized by adaptive immune responses that are incorrectly directed against healthy cells and tissues.
Prevalence: Autoimmune diseases are more common in developed countries and tend to be more prevalent in females.

Definition of Autoimmunity: Autoimmunity resembles hypersensitivity reactions, specifically types II, III, or IV.
Dependency on Effector Mechanisms: Autoimmunity's impact depends on the effector mechanism involved, categorized as follows:
- Type II Hypersensitivity: Mediated by antibodies.
- Type III Hypersensitivity: Mediated by soluble immune complexes.
- Type IV Hypersensitivity: Mediated by effector T cells.

Mechanism: These conditions primarily affect blood cells.
Example: Autoimmune Hemolytic Anemia
- Pathophysiology: Antibodies IgG and IgM target red blood cells.
- Result: Activation of the classical pathway leads to lysis (destruction) or opsonization (marking for phagocytosis) of red blood cells.

Figure 16.2 Explanation: Illustrates the process where erythrocytes bind to anti-erythrocyte autoantibodies, leading to complement fixation and intravascular hemolysis, followed by phagocytosis and destruction of erythrocytes.

Neutropenia: Neutrophils are opsonized by antibodies, leading to their destruction by macrophages.
- Treatment: Splenectomy (surgical removal of the spleen).
Goodpasture’s Syndrome: An antibody response targets extracellular matrix components, specifically collagen.
- Consequences: Triggers inflammatory responses leading to kidney failure and potentially death.
- Treatment Options: Includes plasma exchange therapy and immunosuppressive drugs.

Mechanism: IgG gets produced against cell surface self-antigens, leading to the formation of immune complexes.
Pathology: These complexes are deposited in various tissues, causing inflammation.
Symptoms: Vary depending on where deposits occur:
- Kidneys: Leads to glomerulonephritis.
- Joints: Causes arthritis.
- Skin: Produces a characteristic butterfly rash (erythema).
- Others: Lung inflammation, hair loss, paralysis, and convulsions.

Mechanism: Self-reactive effector CD4 T cells and IFN-γ attack the myelin sheath of nerve cells.
Outcome: Leads to plaques formation in the central nervous system (CNS) and recruitment of macrophages for further attack, potentially crossing the blood-brain barrier.
Symptoms:
- Motor weakness,
- Impaired vision,
- Lack of coordination,
- Spasticity.
- The disease often alternates between phases of recovery and relapse.
Treatment: Involves the use of autoimmune drugs.

Concept: Autoimmunity arises when the self-tolerance mechanism fails, resulting in the unintended activation of immune responses against self.
Consequences: Chronic inflammation and subsequent tissue damage occur.
Genetic link: Example is Canale-Smith Syndrome, where self-reactive lymphocytes are persistently stimulated, leading to chronic lymphadenopathy (swollen lymph nodes).

Basic Mechanism: Two primary mechanisms result from autoantibodies:
- Receptor Agonists: Autoantibodies mimic the natural ligand, causing intracellular activation.
- Receptor Antagonists: Autoantibodies block the natural ligand from binding, halting intracellular activation.

Graves' Disease:
- Nature: An organ-specific autoimmune disorder affecting the thyroid.
- Mechanism: Agonist autoantibodies target the TSH receptor, leading to excessive production of thyroid hormones, independent of actual TSH signaling.
- Symptoms: Include heat intolerance, nervousness/irritability, warm moist skin, weight loss, enlarged thyroid gland, and bulging eyes (Graves’ ophthalmopathy).
Myasthenia Gravis:
- Nature: Impacts signaling from nerves to muscles.
- Mechanism: Antagonistic autoantibodies impair acetylcholine receptors on muscle cells, leading to progressive muscle weakness and respiratory difficulties.
- Treatment: Strategies focus on preventing degradation of acetylcholine to restore function.
Rheumatoid Arthritis:
- Mechanism: Chronic joint inflammation is a result of autoantibodies (IgM, IgG, IgA) against the Fc portion of IgG, referred to as rheumatoid factor.
- Pathology: White blood cell activation and macrophage involvement result in extensive joint damage.
- Treatment: Primarily symptomatic and may include anti-inflammatory and immunosuppressive therapies.

Nature: An autoimmune disorder resulting in the destruction of insulin-producing cells in the pancreas, leading to uncontrolled blood glucose levels and potential coma or death without treatment.

Definition: An inflammatory autoimmune disease of the gut where the immune system reacts to gluten in wheat flour.
Mechanism: T cells and macrophages become activated, resulting in inflammation that blunts villi in the gut, leading to:
- Malabsorption of nutrients,
- Diarrhea,
- Potential for anemia.
Treatment: Requires strict adherence to a gluten-free diet to alleviate symptoms.

Presentation: At age 16, she presented with symptoms including:
- Tremors,
- Difficulty gaining weight,
- Cold intolerance.
Diagnosis: Abnormal levels of T3 and T4 hormones, along with the presence of autoantibodies against thyroid receptors.
Initial Treatment: Managed symptoms with blood pressure medication and regular blood tests for two years to monitor hormone levels.
Subsequent Findings: Persistent hyperthyroidism led to consideration of radioactive iodine treatment or thyroidectomy.
Surgical Complications: Outpatient surgery for thyroid removal extended to 6 hours, resulting in the discovery of thyroid cancer.
Post-operative Management:
- Radioactive iodine to address cancer,
- Thyroid hormone replacement therapy introduced,
- Adjustments in medicine dosage over months to manage cancer and thyroid hormone levels.
- Annual ultrasound checks to monitor for cancer progression or regression.

Autoimmune disorders typically stem from broken self-tolerance, leading to chronic immune responses that target the body’s own tissues. The examples and treatments illustrate the complexity and necessity of tailored therapeutic approaches for each unique disorder.