Certain children are immune to certain disease due to

Options

A. T-cells immune system
B. B-cells immune system
C. Memory cells
D. Phagocyte-antigen reaction

Answer

### Step-by-Step Solution:

1. **Understanding Immunity**: Immunity refers to the body's ability to resist or fight off infections and diseases. It can be classified into two main types: innate immunity (which is present from birth) and adaptive immunity (which develops over time).

2. **Role of Antigens**: Antigens are substances that can induce an immune response. When a child is exposed to a disease-causing pathogen (antigen), the immune system recognizes it as foreign.

3. **First Exposure**: Upon the first exposure to an antigen, the immune system generates an immune response. This involves the activation of various immune cells that work to eliminate the pathogen. During this process, the body produces specific antibodies and activates T cells.

4. **Memory Cells Formation**: After the initial immune response, the body creates memory cells. These cells "remember" the specific antigen and remain in the body long after the infection has been cleared. This is a crucial aspect of adaptive immunity.

5. **Subsequent Exposure**: If the same antigen enters the body again (second exposure), the memory cells recognize it immediately. The immune system can respond more rapidly and effectively, often neutralizing the pathogen before it can cause illness.

6. **Active Immunity**: The immunity that develops as a result of exposure to an antigen and the subsequent formation of memory cells is known as active immunity. This is why certain children may be immune to certain diseases—they have already been exposed to the pathogen and have developed the necessary memory cells.

7. **Conclusion**: Therefore, certain children are immune to certain diseases due to the presence of memory cells formed after their first exposure to the disease-causing pathogens, which allows for a quicker and more effective immune response upon subsequent exposures.