The innate immune system is one of the two main immunity strategies found in vertebrates (the other being the adaptive immune system). The innate immune system is an older evolutionary defense strategy, relatively speaking, and is the dominant immune system response found in plants, fungi, insects, and primitive multicellular organisms.
The major functions of the vertebrate innate immune system include:
- Recruiting immune cells to sites of infection through the production of chemical factors, including specialized chemical mediators called cytokines
- Activation of the complement cascade to identify bacteria, activate cells, and promote clearance of antibody complexes or dead cells
- Identification and removal of foreign substances present in organs, tissues, blood and lymph, by specialized white blood cells
- Activation of the adaptive immune system through a process known as antigen presentation
- Acting as a physical and chemical barrier to infectious agents; via physical measures like skin or tree bark and chemical measures like clotting factors in blood or sap from a tree, which are released following a contusion or other injury that breaks through the first-line physical barrier (not to be confused with a second-line physical or chemical barrier, such as the blood-brain barrier, which protects the extremely vital and highly sensitive nervous system from pathogens that have already gained access to the host’s body).
Image 1: By Architha Srinivasan – Own work, CC BY-SA 3.0