Example of second line of defence in immunity is?

Options

A. Antibodies
B. NK cell
C. Mucosa
D. T-cell

Answer

To solve the question "Example of second line of defence in immunity is?", we will analyze the options provided and determine which one fits the criteria for the second line of defense in the immune system.

### Step-by-Step Solution:

1. **Understand the Concept of Immunity**:
- The immune system has multiple lines of defense. The first line includes physical and chemical barriers (like skin and mucous membranes), while the second line consists of cells that respond to infections in a generalized manner.

2. **Evaluate Each Option**:
- **Option A: Antibodies**:
- Antibodies are proteins produced by B cells that specifically target antigens (foreign substances). Since they are specific to particular pathogens, they do not fit the second line of defense, which is non-specific.
- **Conclusion**: Incorrect.

- **Option B: NK Cells (Natural Killer Cells)**:
- NK cells are a type of white blood cell that play a crucial role in the innate immune response. They attack infected cells and tumor cells without the need for specific antigens, making them part of the second line of defense.
- **Conclusion**: Correct.

- **Option C: Mucosa**:
- Mucosa refers to the lining of various organs and does not actively participate in the immune response. While it serves as a barrier, it is not considered part of the second line of defense.
- **Conclusion**: Incorrect.

- **Option D: T Cells**:
- T cells, specifically T lymphocytes, are involved in the adaptive immune response and are responsible for targeting specific pathogens. They help in recognizing and responding to specific antigens, thus not fitting the criteria for the second line of defense.
- **Conclusion**: Incorrect.

3. **Final Answer**:
- Based on the analysis, the example of the second line of defense in immunity is **B. NK cells**.