The cytokine barrier among these is

Options

A. Polymorphonuclear neutrophil
B. NK cells
C. Interferon
D. Macrophage

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about the "cytokine barrier" among the given options. To answer this, we need to identify what a cytokine barrier is in the context of immunity.

2. **Types of Immunity**: There are two main types of immunity: innate (inborn) and adaptive (acquired). The question pertains to innate immunity, which includes various barriers that prevent pathogen entry.

3. **Identifying Barriers**:
- **Physical Barriers**: These include the skin and mucous membranes that act as the first line of defense against pathogens.
- **Physiological Barriers**: These consist of body secretions such as earwax, lysozyme in sweat and saliva, and hydrochloric acid in the stomach that help neutralize pathogens.
- **Cellular Barriers**: These involve immune cells like polymorphonuclear leukocytes, monocytes, and macrophages that actively fight infections.

4. **Cytokine Barrier**: The specific cytokine barrier referred to in the question is interferons. Interferons are proteins secreted by virus-infected cells that help protect neighboring healthy cells from viral infection by coating them.

5. **Conclusion**: Among the options provided, the only cytokine barrier is interferons. Therefore, the correct answer to the question is option 3, which represents the cytokine barrier.

### Final Answer:
The cytokine barrier among these is **interferons** (option 3).

---