Example of second line of defence in immunity is?

Options

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

Answer

To find the example of the second line of defense in immunity, we will analyze the given options step by step.

### Step 1: Understand the Concept of Immunity
Immunity is the body's ability to resist infections and diseases. It is categorized into two main lines of defense:
- **First Line of Defense**: This includes physical and chemical barriers (like skin and mucous membranes).
- **Second Line of Defense**: This involves non-specific immune responses that act when pathogens breach the first line.

### Step 2: Analyze the Options
We have four options to evaluate:
1. **Antibodies**
2. **NK Cells (Natural Killer Cells)**
3. **Mucosa**
4. **T Cells**

### Step 3: Evaluate Each Option
- **Option 1: Antibodies**
Antibodies are proteins produced by B cells in response to specific antigens. They are part of the adaptive immune response, which is specific. Therefore, this option does not represent the second line of defense.

- **Option 2: NK Cells**
NK cells are a type of white blood cell that plays a crucial role in the innate immune response. They attack and destroy virus-infected cells and tumor cells without the need for prior sensitization to specific antigens. This makes them a key component of the second line of defense.

- **Option 3: Mucosa**
Mucosa refers to the moist tissue lining certain organs and body cavities. While it serves as a barrier, it is part of the first line of defense, not the second.

- **Option 4: T Cells**
T cells are involved in the adaptive immune response and are specific to particular antigens. They are not part of the second line of defense.

### Step 4: Conclusion
Based on the analysis, the correct answer is **B: NK Cells**, as they exemplify the non-specific immune response characteristic of the second line of defense.

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