Which of the following is not a part of innate immunity?

Options

A. T-cell
B. Macrophage
C. HCl in stomach
D. Skin

Answer

To determine which of the following is not a part of innate immunity, we need to first understand what innate immunity is and then analyze the options provided.

### Step-by-Step Solution:

1. **Understanding Innate Immunity**:
- Innate immunity is the body's first line of defense against pathogens. It is a non-specific response that acts immediately or within hours of an antigen's appearance.
- Components of innate immunity include physical barriers (like skin), chemical barriers (like stomach acid), and immune cells (like macrophages).

2. **Analyzing the Options**:
- **Option 1: T-cell**:
- T-cells are a type of lymphocyte that play a crucial role in adaptive immunity, not innate immunity. They are involved in the specific immune response and take longer to activate.
- **Option 2: Macrophage**:
- Macrophages are part of the innate immune system. They are immune cells that engulf and digest pathogens and cellular debris.
- **Option 3: HCl in stomach**:
- Hydrochloric acid (HCl) in the stomach is a chemical barrier that helps kill pathogens, making it a part of innate immunity.
- **Option 4: Hissing**:
- Hissing could refer to a physical reaction (like a hiss of a snake), but if interpreted as a reference to a physical barrier or response, it would still fall under innate immunity.

3. **Conclusion**:
- The only option that is not part of innate immunity is **T-cell**. Therefore, the answer to the question is T-cell.

### Final Answer:
**T-cell** is not a part of innate immunity.