Innate immune system

The innate immune system 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, 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.

The innate immune system is thought to constitute an evolutionarily older defense strategy, and is the dominant immune system found in plants, fungi, insects, and in 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 specialized white blood cells.
• Activation of the adaptive immune system through a process known as antigen presentation.

Anatomical barriers

The epithelial surfaces form a physical barrier that is very impermeable to most infectious agents, acting as the first line of defense against...
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