Innate immune system

The innate, or nonspecific, immune system is one of the two main immunity strategies (the other being the adaptive immune system) in vertebrates. The innate immune system is an alternate defense strategy and is the dominant immune system response found in plants, fungi, prokaryotes, and invertebrates (see Beyond vertebrates).

The major functions of the innate immune system are to:

• recruit immune cells to infection sites by producing chemical factors, including chemical mediators called cytokines
• activate the complement cascade to identify bacteria, activate cells, and promote clearance of antibody complexes or dead cells
• identify and remove foreign substances present in organs, tissues, blood and lymph, by specialized white blood cells
• activate the adaptive immune system through antigen presentation
• act as a physical and chemical barrier to infectious agents; via physical measures such as skin and mucus, and chemical measures such as clotting factors and host defence peptides.