Vaccination works by producing

Options

A. Antibody which stays in blood
B. Memory lymphocytes
C. Constant stimulation of immune system
D. All the above

Answer

### Step-by-Step Solution:

1. **Understanding Vaccination**: Vaccination is a method used to stimulate the immune system by introducing a harmless form of a pathogen (antigenic material) into the body. This helps the body to prepare itself to fight off the actual pathogen in the future.

2. **Role of Antigens**: The vaccine contains antigens that mimic the pathogen. When introduced into the body, these antigens trigger an immune response.

3. **Immune Response Activation**: The immune system recognizes these antigens as foreign invaders. This leads to the activation of various immune cells, including B cells and T cells.

4. **Production of Antibodies**: B cells are responsible for producing antibodies. These antibodies specifically target the antigens introduced by the vaccine. However, the immediate production of antibodies occurs when the body encounters the actual pathogen after vaccination.

5. **Formation of Memory Lymphocytes**: One of the key outcomes of vaccination is the formation of memory lymphocytes (specifically memory B cells). These cells remain in the body long after the vaccination has taken place.

6. **Future Immune Response**: If the body encounters the same pathogen in the future, these memory lymphocytes quickly recognize the antigen and initiate a rapid immune response by producing antibodies. This is what provides long-term immunity.

7. **Conclusion**: Therefore, vaccination primarily works by producing memory lymphocytes that enable the body to respond quickly and effectively to future infections by the same pathogen.

### Final Answer:
Vaccination works by producing **memory lymphocytes**.

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