Transplantation of tissues/organs to save certain patients often fails due to rejection of such tissues/organs by the patient. Which type of immune response is responsible for such rejections?

Options

A. Auto-immune response
B. Humoral immune response
C. Physiological immune response
D. Cell-mediated immune response

Answer

To answer the question regarding the type of immune response responsible for the rejection of transplanted tissues or organs, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Transplantation**: When tissues or organs are transplanted from a donor to a recipient, the recipient's immune system may recognize the transplanted tissue as foreign.

2. **Immune System Response**: The immune system has various mechanisms to protect the body from foreign substances. One of the primary responses involved in rejecting transplanted tissues is the immune response.

3. **Types of Immune Response**: There are two main types of immune responses:
- **Humoral Immune Response**: This involves the production of antibodies by B cells.
- **Cell-Mediated Immune Response**: This involves T cells, including cytotoxic T lymphocytes (CTLs), which directly attack and destroy infected or foreign cells.

4. **Cell-Mediated Immune Response**: In the case of organ transplantation, the rejection is primarily due to the cell-mediated immune response. This response does not involve antibodies but rather involves:
- Activation of macrophages.
- Activation of natural killer (NK) cells.
- Activation of cytotoxic T lymphocytes (CTLs) that recognize and destroy the foreign cells.

5. **Antigen Recognition**: When the transplanted organ is introduced into the recipient's body, the recipient's immune system detects the antigens present on the cells of the transplanted organ. If these antigens are not compatible with the recipient's own cells, the immune system mounts a response against them.

6. **Result of Immune Response**: The activation of these immune cells leads to the destruction of the transplanted tissue or organ, resulting in rejection.

### Conclusion:
The type of immune response responsible for the rejection of transplanted tissues or organs is the **cell-mediated immune response**.

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