Second Line of Defense: Natural Killer Cells, Interferons, and Fever

Fight viruses, nonspecific.
Viruses:
- Have a boundary/wall.
- Contain DNA or RNA (nucleic acid).
- Lack cellular parts and use host cells to replicate.
- Insert genetic information into host cell genetic information.
- Host cells then make more viruses.
Interferon Mechanism:
- Infected cells send out a "mayday signal" via interferons.
- Interferons prevent adjacent cells from allowing virus access to the nucleus.
- Interferons block the virus from commandeering adjacent cells.
Second line of defense, works against viruses.
Not targeted at a specific singular virus.

To a certain degree, fever is beneficial.
Leukocytes and macrophages secrete pyrogens.
- Pyrogens signal the hypothalamus (body temperature regulator) to raise body temperature.
Reasons for fever:
- Makes the body inhospitable to pathogens.
  - $98.6^{\circ}F$ is a good reproductive temperature for bacteria/viruses.
  - Increased temperature can kill some pathogens.
- Causes liver and spleen to hold back iron and zinc.
  - These elements are needed for microorganism reproduction.
- Increases metabolic rate, increasing the rate of repair.
  Medical Community Stance:
- Up to $101^{\circ}F$ , typically avoid medication to reduce fever as it benefits the body.
- Indicates the body is past the first line of defense and fighting infection.
- Some may allow fevers up to $102^{\circ}F$ .
- Fever makes you feel pretty bad.
  Too High Fever:
- Above $102^{\circ}F$ is generally discouraged because:
  - Enzymes can denature at high temperatures.
  - Risk of denaturing the body's own enzymes.
  - Important to bring the temperature down.
    Kids and Fever:
- Children can quickly spike high fevers (e.g., $104^{\circ}F$ , $105^{\circ}F$ ).
- These very high temperatures need to be reduced as they can be dangerous.

The third line of defense, specific immunity, will be covered in the next module.