Interferons form cytokine barrier/complement system of immunity.

Explanation

**Step-by-Step Solution:**

1. **Understanding Interferons:**
- Interferons are proteins that are produced and released by cells in response to viral infections. They play a crucial role in the immune response.

2. **Function of Interferons:**
- When a cell is infected by a virus, it releases interferons. These interferons act as signaling molecules that alert neighboring non-infected cells about the viral threat.

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