When the same antigen or pathogen enters for a second time in human body, the resultant secondary immune response is stronger than primary immune response due to

Options

A. `T_c` cells only
B. T-helper cells only
C. Memory cells (B and T cells)
D. Plasma cells only

Answer

To answer the question regarding why the secondary immune response is stronger than the primary immune response when the same antigen or pathogen enters the human body for a second time, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding Immune Responses**:
- The immune system has two types of responses: primary and secondary immune responses.
- The primary immune response occurs when the body encounters a pathogen for the first time.

2. **Primary Immune Response**:
- Upon the first encounter with a pathogen, the body does not have pre-existing antibodies.
- The immune system takes time (several days) to recognize the antigen and produce antibodies.
- B-cells are activated and differentiate into plasma cells, which produce antibodies, and memory cells, which remain in the body for a long time.

3. **Memory Cells**:
- Memory B-cells and T-cells are crucial components of the immune system.
- They "remember" the specific antigen and remain in the body for years, sometimes decades.

4. **Secondary Immune Response**:
- When the same pathogen enters the body again, memory cells recognize the antigen quickly.
- These memory cells proliferate rapidly and produce a stronger and faster immune response.
- This response is often referred to as the "booster response" because it is more effective than the primary response.

5. **Characteristics of Secondary Response**:
- The secondary immune response has a higher antibody titer (concentration) and occurs in a shorter time frame compared to the primary response.
- This enhanced response is due to the presence of memory B-cells and T-cells that were generated during the primary response.

6. **Conclusion**:
- The stronger secondary immune response is primarily due to the memory cells (B and T cells) that were formed during the primary immune response.

### Final Answer:
The resultant secondary immune response is stronger than the primary immune response due to memory cells (B and T cells).

---