Vaccines are

Options

A. Curative medicines
B. Monoclonal antibodies
C. Treated bacteria or viruses or one of their proteins
D. MHC (Major Histocompatibility Complex) proteins

Answer

**Step-by-Step Solution:**

1. **Understanding the Definition of Vaccines:**
- A vaccine is a biological preparation that provides active acquired immunity to a particular infectious disease. It typically contains a weakened or killed form of the microbe (virus or bacteria) that causes the disease.

2. **Mechanism of Action:**
- When a vaccine is administered, it stimulates the immune system to recognize the microbe as a threat. This triggers an immune response, which includes the production of antibodies.

3. **Role of Antibodies:**
- Antibodies are specialized proteins produced by white blood cells (WBCs) that specifically target and neutralize pathogens. They help in identifying and eliminating foreign invaders in the body.

4. **Types of Vaccines:**
- Vaccines can be made from weakened (live attenuated) or killed (inactivated) microbes, or even from parts of the microbe such as proteins. This allows the immune system to learn how to fight the actual pathogen without causing the disease.

5. **Evaluating Options:**
- The question provides several options regarding what vaccines are:
- **Option A:** Curable medicines - Incorrect, as these are treatments for diseases.
- **Option B:** Monoclonal antibodies - Incorrect, as these are lab-produced antibodies for specific antigens.
- **Option C:** Treated bacteria or viruses or one of their proteins - Correct, as this describes the components of vaccines.
- **Option D:** Major histocompatibility complex protein - Incorrect, as these are proteins that help in immune recognition and are not vaccines.

6. **Conclusion:**
- The correct answer is **Option C**, as vaccines are indeed treated (weakened or killed) forms of bacteria or viruses or their proteins that stimulate an immune response.

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