Disorders in Immunity

Immunopathology: Disease state associated with over-reactivity or under-reactivity of the immune response.
Types of Disorders:
- Type I: Immediate hypersensitivity (e.g., hay fever, anaphylaxis)
- Type II: Antibody-mediated (e.g., blood type incompatibilities)
- Type III: Immune complex diseases (e.g., rheumatoid arthritis)
- Type IV: Cell-mediated (e.g., graft rejection, contact dermatitis)

Allergy: An exaggerated immune response to an allergen, immediate reaction.
- Atopy: Chronic allergies (e.g., hay fever, eczema).
- Anaphylaxis: Severe, systemic reaction; can lead to airway obstruction and circulatory collapse.
Sensitization Process:
1. Allergens enter mucous membrane.
2. Dendritic cells present the allergen to T helper cells.
3. B cells produce IgE specific to allergens.
4. IgE binds to mast cells, priming for future exposure.
5. Upon subsequent exposure, allergens bind to IgE on mast cells leading to degranulation and allergic symptoms.
Symptoms: Itching, hives, respiratory distress, etc.
Common Allergens: Pollens, molds, food items (e.g., peanuts, dairy).
Diagnosis: Skin testing to observe wheal response.
Treatment: Avoidance, antihistamines, corticosteroids, desensitization therapy.

Blood Types: Determined by the presence of A and B antigens on RBCs; 4 blood types: A, B, AB, O.
- Antibodies: Type A has anti-B, Type B has anti-A, Type AB has none, Type O has both anti-A and anti-B.
Hemolytic Reactions: Agglutination and destruction of RBCs can occur if incompatible blood types are mixed.
Rh Factor: Important in pregnancy; Rh- mothers can develop antibodies against Rh+ fetuses leading to hemolytic disease of the newborn (HDN).
Prevention: Administer RhoGAM to Rh- pregnant women to prevent sensitization.

Mechanism: Antibodies react with soluble antigens to form immune complexes that can deposit in tissues.
Examples: Systemic lupus erythematosus, rheumatoid arthritis, serum sickness.
Symptoms: Vary based on the location of immune complex deposition (e.g., joints, kidneys).

Delayed Hypersensitivity: Symptoms occur 1-3 days after exposure due to T cell responses against antigens.
Contact Dermatitis: Allergic reaction from skin contact with certain agents (e.g., poison ivy).
Organ Transplant Rejection: T cells can recognize grafted tissue as foreign, leading to its destruction.
Types of Grafts:
- Autograft: Tissue from the same individual.
- Isograft: Tissue from genetically identical twin.
- Allograft: Tissue from another individual of the same species.
- Xenograft: Tissue from a different species.

Definitions: Diseases where the immune system attacks the body's own cells.
Types:
- Systemic: Affects multiple organs (e.g., systemic lupus erythematosus).
- Organ-Specific: Targets specific organs (e.g., Hashimoto's thyroiditis).
Theories of Autoimmune Origin:
1. Sequestered antigen theory: Exposure of hidden antigens due to trauma.
2. Clonal selection theory: Survival of self-reactive lymphocytes that attack self-cells.
3. Immune deficiency theory: Mutations in lymphocyte receptors causing self-reactivity.
4. Molecular mimicry: Pathogen antigens resembling self-antigens leading to cross-reactive responses.

Primary Immunodeficiencies: Genetic defects present at birth (e.g., SCID).
Secondary Immunodeficiencies: Acquired post-birth due to infections, aging, stress, or immunosuppressive agents.
Examples:
- Agammaglobulinemia: Lack of antibodies.
- DiGeorge syndrome: Absence of T cells.
- HIV/AIDS: Viral infections leading to immune system collapse.