Course Hero Logo

Innate Immunity



The innate immune system is the body’s first line of defense against pathogens and uses a combination of various tissues, immune cells, and barriers for protection. The skin, the mucosal layers, and the lymphatic system are each involved in innate immunity. Innate immunity quickly detects microbial molecules and responds with nonspecific antimicrobial attacks, including inflammation and white blood cells, to prevent infection. Innate immunity acts to stop infections before they start, whereas adaptive immunity uses a different set of tools to eliminate infections in progress. The complement system is composed of inactive proteins found in the bloodstream that when activated can trigger immune responses such as inflammation and phagocytosis.

At A Glance

  • Innate immunity is the first and second line of immune defense: barriers that prevent entry into the body and nonspecific reactions that prevent infections from taking hold.
  • The first line of immune defense is made up of physical and chemical barriers such as the skin, sweat, tears, and mucous membranes, which prevent pathogens from reaching more vulnerable areas of the body.
  • The second line of immune defense is the collection of cells and fluids that provide a nonspecific reaction against invading pathogens.
  • The lymphatic system includes a network of vessels and tissues that carry immune cells from lymphatic organs to the rest of the body, providing surveillance to monitor potential infection, draining fluid from inflammatory responses, and providing a route for immune cells to reach sites of infection.
  • The complement system is an important part of the immune system that enhances the activity of white blood cells and antibodies to target invading microbes and damaged host cells.
  • White blood cells are a collection of different immune cell types that respond to inflammation and directly attack invading pathogens during an innate immune response.