## Core Concept
Innate immunity provides the first line of defense against infections and is crucial for controlling viral infections. It comprises various components, including physical barriers, cells, and proteins, that work together to recognize and eliminate pathogens. The key components active against viral cells include interferons, natural killer cells, and certain types of leukocytes.

## Why the Correct Answer is Right
The correct answer, interferons, are proteins that are critical in the innate immune response against viral infections. They are produced by host cells in response to the presence of viruses and have antiviral effects. Interferons can induce cells to produce antiviral proteins, inhibit viral replication, and activate immune cells such as natural killer cells and macrophages. This mechanism is vital for limiting the spread of viruses within the host.

## Why Each Wrong Option is Incorrect
- **Option A:** While complement system and lysozyme do play roles in innate immunity, they are not as directly active against viral cells as interferons. The complement system can help lyse viral particles or mark them for destruction, but it's not the most specific or potent mechanism against viral infections.
- **Option B:** This option might refer to other components of the immune system, but without specifics, it's hard to directly refute. However, if it implies adaptive immunity components, those are not part of innate immunity.
- **Option C:** This could potentially refer to cells like neutrophils and macrophages, which are important in innate immunity but are more broadly active against bacteria, fungi, and other pathogens, not specifically targeting viral infections as directly as interferons.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **interferons** are crucial for the innate immune response against viral infections. They not only have direct antiviral effects but also help in activating other immune responses. This is a high-yield fact because understanding the role of interferons can help in grasping how the body initially responds to viral infections and how some antiviral therapies work.

## Correct Answer: D. Interferons.