🫀Type IV hypersensitivity

Question 1

What is the mechanism of type IV hypersensitivity?

Answer 1

Cd4+ (esp Th1 Th17) mediated pro inflammatory ck release -> MP/nk cell recruitment-> tissue dmg

Question 2

Why is type IV considered “delayed”?

Answer 2

mediated by adaptive IR (cd4+ cells) -> onset 2-3 days after Ag exposurw

Question 3

What is the role of CD4+ T cells in type IV hypersensitivity?

Answer 3

• Activation: CD4+ T cells → antigen on APCs (e.g., macrophages)
• Cytokine Release: Secrete IFN-γ, TNF-α → recruit macrophages, neutrophils
• Inflammation: Inflammatory response → tissue damage

Question 4

What is the role of macrophages in delayed-type hypersensitivity?

Answer 4

• Activation: CD4+ T cell cytokines (e.g., IFN-γ) → macrophage activation
• Inflammation: Release TNF-α, chemokines
• Tissue Damage: Phagocytosis, ROS, enzyme release → tissue damage

Question 5

How do CD8+ cytotoxic T cells contribute to tissue damage?

Answer 5

• Recognition: CD8+ T cells → MHC I on APCs (foreign/altered self-antigens)
• Cytotoxicity: Perforin, granzymes → apoptosis of target cells
• Inflammation: IFN-γ, TNF-α → amplify tissue damage

Question 6

What is the basis of the tuberculin skin test (Mantoux test)?

Answer 6

• Basis: Type IV hypersensitivity, PPD of Mycobacterium tuberculosis
• Response: Sensitized CD4+ T cells → cytokine release → erythema & induration (24-72 hrs)

Question 7

What is contact dermatitis and how is it caused immunologically?

Answer 7

• Contact Dermatitis: Type IV hypersensitivity (delayed-type) reaction
• Cause: Sensitization to allergen (e.g., poison ivy, nickel) → CD8+ T cells, macrophages, cytokines
• Mechanism: T cell-mediated inflammation → skin rash, erythema, edema

Question 8

How is type 1 diabetes also a type IV hypersensitivity?

Answer 8

• T1D = Type IV Hypersensitivity
• CD4+/CD8+ T cells → Recognize self-antigens (e.g., insulin, GAD) on β-cells
• Cytotoxicity → β-cell destruction → Loss of insulin production

Question 9

What is the role of granuloma formation in type IV reactions?

Answer 9

• Granuloma Formation: Chronic inflammation in type IV reactions
• Cause: Persistent antigen exposure → macrophages, T cells, fibroblasts aggregate
• Function: Contain and isolate pathogens, but can cause tissue damage over time
• Key Cells: Macrophages, multinucleated giant cells, CD4+ T cells