Human Body's Three Lines of Defense

By: Shawn Huang and Nikhil Padmanabhan

First Line of Defense: Innate

The first line of defense is composed of one's skin, stomach, mucus, hair, sweat, tears, etc. These are physical barriers that aim to block out pathogens.

Second Line of Defense: Adaptative

The second line of defense consists of inflammatory responses and phagocytosis. The inflammatory responses include these four symptoms: redness, swelling, pain, and heat. Phagocytes such as macrophages and neutrophils search and destroy pathogens by engulfing them. This is a non-specific reaction because it doesn't require specific targeting.

Third Line of Defense: Acquired

The third line of defense is specific. Helper T cells and B cells are produced at this time. Antibodies are also created. They bind to the pathogens and serve as an immune system indicators showing that the pathogens are the target to attack.