Immunity can be defined as the ability of an organism to resiste the pathogenic harm caused by another living organism, or to resist the allergic reactions mediated by the components of living organisms.
Innate immunity is the inborn and inherent mechanism that an organism is born with. These are present since birth of an individual and are responsible for providing the first line of defense to the body. It is also known as non-specific immunity. The components of the innate immunity are as follows:
1. The anatomical or chemical barriers- these include the skin, mucous membrane, gastro-intestinal tract, urino-genital tract and respiratory tract that are responsible of preventing the entry of pathogen or to trap the pathogen during its entry in the body.
2. The phagocytic barriers- these include the leukocytes present in blood that are capable of performing phagocytosis and killing the pathogen, for example, macrophages, neutrophils, natural killer cells.
3. Plasma proteins- plasma of the blood is rich in proteins that perform immnulogical functions, such as the complement proteins that inform phagocytic cells about a pathogen and also trigger production of antibodies.
4. Cytokines- these are the proteins produced by the epithelial cells (dendritic cells), neutrophils, macrophages that control the growth and spread of infection.