Which one of the cell of cellular barrier of innate immunity is not involved in phagocytosis :-

Options

A. Monocyte
B. Macrophage
C. PMNL-neutrophil
D. Natural killer cell

Answer

To solve the question regarding which cell of the cellular barrier of innate immunity is not involved in phagocytosis, we can follow these steps:

### Step 1: Understand the Cells Involved in Innate Immunity
Innate immunity consists of various cells that respond to pathogens. The key cells include:
- Monocytes
- Macrophages
- Neutrophils (PMNL)
- Natural Killer (NK) cells

### Step 2: Identify the Function of Each Cell Type
- **Monocytes**: These are precursors to macrophages and are involved in phagocytosis.
- **Macrophages**: These cells are derived from monocytes and are highly effective at engulfing and digesting pathogens through phagocytosis.
- **Neutrophils (PMNL)**: These are the most abundant type of white blood cells and are also involved in phagocytosis, targeting bacteria and fungi.
- **Natural Killer (NK) Cells**: These cells are part of the innate immune response but do not perform phagocytosis. Instead, they kill infected or cancerous cells by inducing apoptosis (programmed cell death) and forming pores in the target cell membranes.

### Step 3: Determine Which Cell is Not Involved in Phagocytosis
From the functions outlined:
- Monocytes, macrophages, and neutrophils are all involved in phagocytosis.
- Natural Killer cells do not engage in phagocytosis; they kill cells through a different mechanism.

### Conclusion
Based on the above analysis, the cell of the cellular barrier of innate immunity that is not involved in phagocytosis is **Natural Killer (NK) cells**.

### Final Answer
The correct answer is **Natural Killer cells** (Option 4).

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