Neutrophils and monocytes are important cells participating in:

Options

A. phagocytosis
B. perforin production
C. passive immunity
D. antibody production

Answer

### Step-by-Step Solution

1. **Understanding the Cells Involved**: Neutrophils and monocytes are types of white blood cells (leukocytes) that play crucial roles in the immune response. Neutrophils are the most abundant type of white blood cells, making up about 60-65% of the total white blood cell count, while monocytes constitute about 2-10%.

2. **Function of Neutrophils**: Neutrophils are primarily responsible for the first line of defense against infections. They are motile and can quickly move to sites of microbial invasion. Their main function is to engulf and destroy pathogens, which is a process known as phagocytosis.

3. **Function of Monocytes**: Monocytes, which are the largest type of leukocytes, also play a significant role in the immune response. Once they migrate to tissues, they can differentiate into macrophages, which are highly effective phagocytic cells. Like neutrophils, monocytes also participate in phagocytosis.

4. **Phagocytosis Process**: Phagocytosis is the process by which cells, such as neutrophils and monocytes, engulf and digest foreign particles, including bacteria and cellular debris. This process is essential for clearing infections and initiating the healing process.

5. **Conclusion**: Given that both neutrophils and monocytes are involved in the process of phagocytosis, the correct answer to the question is option one: phagocytosis.

### Final Answer
**Neutrophils and monocytes are important cells participating in phagocytosis.**

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