Patho Wk 4 - Hypersensitivities

Overview of Hypersensitive Immune Responses

• 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.

Type 1 Hypersensitivity

• 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.

Type 2 Hypersensitivity

• 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.

Type 3 Hypersensitivity

• 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.

Type 4 Hypersensitivity

• 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.

Summary Mnemonic

• 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)

Overview of Hypersensitive Immune Responses

• 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.

Type 1 Hypersensitivity

• 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.

Type 2 Hypersensitivity

• 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.

Type 3 Hypersensitivity

• 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.

Type 4 Hypersensitivity

• 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.

Summary Mnemonic

• 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)