The innate immune system, also known as non-specific immune system and first line of defense, is a subsystem of the overall immune system that comprises the cells and mechanisms that defend the host from infection by other organisms in a non-specific manner. This means that the cells of the innate system recognize and respond to pathogens in a generic way, but, unlike the adaptive immune system (which is found only in vertebrates), it does not confer long-lasting or protective immunity to the host. Innate immune systems provide immediate defense against infection, and are found in all classes of plant and animal life. They include both humoral immunity components and cell-mediated immunity components.
The innate immune system is an evolutionarily older defense strategy, and is the dominant immune system 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 to promote clearance of dead cells or antibody complexes
The identification and removal of foreign substances present in organs, tissues, the blood and lymph, by specialised 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.