Q.3 Type IV- delayed hypersensitivity is not caused by
I. Macrophage
2. Lymphokines
3. Circulating antibodies
4. T- cells
Type IV delayed hypersensitivity is a cell-mediated immune response driven by T-cells, not circulating antibodies, so option 3 is the correct answer for what does not cause it.
Option Analysis
1. Macrophage
Macrophages are key effector cells activated by cytokines from sensitized T-cells, amplifying inflammation and tissue damage in type IV reactions like tuberculin tests.
2. Lymphokines
Lymphokines (e.g., IFN-γ, IL-2 from Th1 cells) are secreted by activated T-cells to recruit and activate macrophages, driving the delayed response over 24-72 hours.
3. Circulating antibodies
Type IV hypersensitivity is purely cell-mediated, independent of antibodies, unlike types I-III which involve humoral immunity; no B-cell or antibody role here.
4. T-cells
Sensitized CD4+ Th1 cells and CD8+ cytotoxic T-cells recognize antigen on MHC, initiating the cascade via cytokine release and direct cytotoxicity.
Type IV delayed hypersensitivity, a T-cell driven immune reaction, is not caused by circulating antibodies but involves macrophages, lymphokines, and T-cells in delayed responses like contact dermatitis.
Mechanism Overview
Antigen presentation sensitizes CD4+ and CD8+ T-cells during initial exposure. Re-exposure triggers Th1 cytokine (lymphokine) release, macrophage recruitment, and inflammation peaking at 48-72 hours.
Role of Each Component
-
T-cells: Initiate via antigen recognition on APCs.
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Lymphokines: Recruit/activate effectors (e.g., IFN-γ).
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Macrophages: Cause tissue damage via enzymes.
| Component | Role in Type IV | Antibody Link? |
|---|---|---|
| Macrophages | Effector damage | No |
| Lymphokines | Cytokine mediation | No |
| Circulating antibodies | Absent (cell-mediated only) | Yes (types I-III) |
| T-cells | Sensitization/activation | No |
Ideal for molecular biology and microbiology exam prep, distinguishing cell-mediated from antibody responses.
