Patho Wk 4 - Hypersensitivities

Hypersensitivity disorders occur when the immune system overreacts to stimuli, causing inflammation, cellular damage, and potentially death.
Divided into four types: Type 1, Type 2, Type 3, Type 4.

Also known as IgE-mediated hypersensitivity.
Antigens are freely moving and can include pollen, bee venom, or peanut proteins.
Primary immune component: IgE antibodies produced by B-cells.
Mechanism involves sensitization; first exposure creates IgE antibodies that attach to mast cells, which can be found in skin and mucous membranes.
Upon re-exposure, the antigen binds to IgE on mast cells, causing them to release histamine, leading to inflammation and symptoms like nasal congestion and watery eyes.
Related diseases include allergic asthma and anaphylaxis, which can result in severe drops in blood pressure and airway obstruction.
Mnemonic for Type 1: "A" for asthma, allergies, anaphylaxis.

Known as cytotoxic hypersensitivity.
The antigen is fixed to the surface of cells.
Primary immune component: IgG or IgM antibodies.
Example: Blood type incompatibility. Type A individuals have antibodies against Type B blood. Transfusion of Type B blood leads to hemolysis of Type A red blood cells.
Other examples include hemolytic anemia in newborns due to Rh factor incompatibility and Goodpasture syndrome, which causes kidney damage due to immune response against collagen.
Mnemonic for Type 2: "C" for cytotoxic.

Immune complex-mediated hypersensitivity.
Antigens and antibodies (typically IgG) are both freely moving in the bloodstream.
Immune complexes form when antibodies bind to soluble antigens, which can lead to tissue deposition.
Example: Post-streptococcal glomerulonephritis where immune complexes deposit in kidneys, causing inflammation.
Also includes systemic lupus erythematosus (SLE), where the body reacts against its own DNA or RNA.
Mnemonic for Type 3: "AI" for immune complex-driven inflammation.

Known as delayed-type hypersensitivity.
Involves T helper cells rather than antibodies; triggered by sensitization to an antigen that is typically movable.
Example: Contact dermatitis from latex allergens; macrophages present the antigen to T helper cells, which become activated and release cytokines 48 to 72 hours later.
Also includes Type 1 diabetes, where the immune response targets insulin-producing beta cells in the pancreas.
Mnemonic for Type 4: "D" for delayed-type responses and dermatitis.

Use "ACID" to remember the four types of hypersensitivity:
- A: Type 1 (Asthma, Allergies, Anaphylaxis)
- C: Type 2 (Cytotoxic)
- I: Type 3 (Immune Complex)
- D: Type 4 (Delayed)

Hypersensitivity disorders arise from the immune system's excessive reaction to stimulus, leading to inflammation and potential fatality.
Classified into four key types: Type 1, Type 2, Type 3, and Type 4.

IgE-mediated hypersensitivity characterized by the production of IgE antibodies from B-cells.
Antigens are typically pollen, insect venom, or food proteins like peanuts.
Initial exposure results in IgE antibodies attaching to mast cells in the skin and mucosal areas.
Subsequent exposure triggers the release of histamine from mast cells, causing symptoms such as nasal congestion and tearing.
Conditions linked to Type 1 include allergic asthma and anaphylaxis, leading to significant drops in blood pressure and difficulty breathing.
Mnemonic: "A" for asthma, allergies, anaphylaxis.

Also referred to as cytotoxic hypersensitivity, where antigens are attached to the surfaces of cells.
Involves IgG or IgM antibodies targeting these fixed antigens.
Notable example: Blood type incompatibility, where Type A individuals produce antibodies against Type B blood, resulting in red blood cell destruction upon transfusion.
Other examples include Rh factor-related hemolytic anemia in newborns and Goodpasture syndrome causing renal damage through collagen targeting.
Mnemonic: "C" for cytotoxic.

Immune complex-mediated hypersensitivity, where antigens and antibodies (usually IgG) circulate freely.
Immune complexes form when antibodies bind to soluble antigens, potentially depositing in tissues and causing damage.
Example: Post-streptococcal glomerulonephritis involves immune deposits in the kidneys, leading to inflammation.
Systemic lupus erythematosus (SLE) features the immune system reacting against the body’s own DNA or RNA.
Mnemonic: "AI" for immune complex-driven inflammation.

Delayed-type hypersensitivity involving T helper cells instead of antibodies.
Triggered by initial sensitization to movable antigens, leading to an immune response 48 to 72 hours later.
Example includes contact dermatitis resulting from latex exposure, where macrophages present the antigen activating T helper cells.
Also encompasses Type 1 diabetes, wherein the immune system attacks insulin-producing pancreatic beta cells.
Mnemonic: "D" for delayed-type responses and dermatitis.

Use "ACID" to remember the four types of hypersensitivity:
- A: Type 1 (Asthma, Allergies, Anaphylaxis)
- C: Type 2 (Cytotoxic)
- I: Type 3 (Immune Complex)
- D: Type 4 (Delayed)