Type-IV hypersensitivity reactions are cell-mediated immune responses caused by cytokines from CD4+ T cells or cytotoxic CD8+ T cells. They involve the proliferation and differentiation of antigen-responsive T cells into subsets like TH1 dominated by macrophages or TH17 dominated by neutrophils. Examples include tuberculosis reactions, contact dermatitis, and autoimmune diseases like rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease, psoriasis, and type 1 diabetes.

1. Type-IV
Hypersensitivity
Reaction
Dr. Arushi
Agarwal
JR-1

2. Hypersensitivity
Reaction
 Injurious immune response
 Exaggerated/inappropriate state of
normal immune response with onset
of adverse effects on the body

3. Types
 Immediate type
 Type I : Anaphylactic
 Type II : Cytotoxic
 Type III : Immune Complex Mediated
 Delayed Type
 Type IV : Cell-Mediated

4. Type IV
Hypersensitivity
 Cell-mediated immune disorders
 Caused by:
 Cytokines produced by CD4+T cells
 Cell killing by CD8+ T cells

5. Activation of CD4+T cells
CD4+T cells
Recognise peptides displayed
by dendritic cells
Secrete IL-
2
Proliferation of antigen-
responsive T cells

6. Differentiation of antigen
responsive T-cells
Antigen presenting cells
TH17 SUBSET
(Dominated by
neutrophils)
TH1 SUBSET
(Dominated by
activated
macrophages)
IL-12 IL-2, IL-3, IL-23

7. Examples:
• Tuberculin reactions
• Granulomatous inflammation
• Contact dermatitis
• Rheumatoid arthritis
• Multiple sclerosis
• Inflammatory Bowel
Disease
• Psoriasis

8. T-cell mediated killing of targets involves:
• Perforins and granzymes
• Activation of apoptosis.
• Examples: Type 1 Diabetes Mellitus

9. Thank you