Which of the following statement is incorrect ?

Options

A. Epitopes are antigen-determing sites which are recognized by antibodies.
B. Nowadays, for the treatment of cancer, the patients are given substances called biological response modifiers such as `alpha`-interferon which activate their immun e system and help in destroying the tumor.
C. Toxoids provide passive immunity.
D. "ATS" (anti tetanus serum) provides us artificially acquired passive immunity.

Answer

To determine which statement is incorrect, let's analyze each statement one by one.

### Step-by-Step Solution:

1. **Understanding Epitopes**:
- Epitopes are parts of an antigen that are recognized by the immune system, specifically by antibodies.
- **Conclusion**: The statement about epitopes being antigen-determining sites recognized by antibodies is **correct**.

2. **Treatment of Cancer with Biological Response Modifiers**:
- Cancer patients are sometimes treated with biological response modifiers, such as alpha interferon, which help activate the immune system to destroy tumor cells.
- **Conclusion**: The statement regarding the treatment of cancer with biological response modifiers is **correct**.

3. **Understanding Toxoids**:
- Toxoids are inactivated toxins that have lost their toxicity but can still elicit an immune response. They are not the same as passive immunity.
- Passive immunity involves the introduction of ready-made antibodies into the body, whereas toxoids stimulate the body to produce its own antibodies.
- **Conclusion**: The statement that toxoids provide passive immunity is **incorrect**; they provide active immunity.

4. **ATS Serum and Passive Immunity**:
- ATS (Anti-Tetanus Serum) provides artificially acquired passive immunity, as it involves the direct introduction of antibodies into the body for immediate protection against pathogens.
- **Conclusion**: The statement about ATS serum providing artificially acquired passive immunity is **correct**.

### Final Conclusion:
The incorrect statement is: "Toxoids provide passive immunity."