Which of the following is not a part of second line of defense in human?

Options

A. Neutrophils
B. Macrophages
C. NK Cells
D. B-lymphocytes

Answer

To determine which of the following is not a part of the second line of defense in humans, we need to understand the components of the immune system and the specific roles they play.

**Step 1: Understand the Second Line of Defense**
The second line of defense in the human immune system consists of non-specific mechanisms that respond to pathogens in a generalized manner. This includes various types of white blood cells and other immune responses that do not target specific pathogens.

**Hint:** The second line of defense includes components that act broadly against invaders rather than specifically targeting them.

**Step 2: Identify Components of the Second Line of Defense**
Key components of the second line of defense include:
- **Phagocytic cells**: Such as neutrophils and macrophages, which ingest and destroy pathogens.
- **Natural killer cells**: These cells help control tumor growth and microbial infections.

**Hint:** Look for cells that are involved in general immune responses, like phagocytosis and tumor control.

**Step 3: Analyze Each Option**
1. **Neutrophils**: These are phagocytic cells that play a crucial role in the second line of defense by ingesting and destroying pathogens.
2. **Macrophages**: These are also phagocytic cells and are a significant part of the second line of defense.
3. **Ankycells (Natural Killer Cells)**: These cells are involved in the immune response against tumors and infections, thus are part of the second line of defense.
4. **B lymphocytes**: These cells are primarily involved in the adaptive immune response, specifically in producing antibodies against specific pathogens.

**Hint:** Differentiate between the innate (non-specific) and adaptive (specific) immune responses when evaluating the options.

**Step 4: Conclusion**
After analyzing the options, we find that:
- Neutrophils, macrophages, and natural killer cells are all part of the second line of defense.
- B lymphocytes, however, are part of the adaptive immune response and not the second line of defense.

Thus, the correct answer is **B lymphocytes**, as they are not part of the second line of defense.

**Final Answer:** B lymphocytes