The innate or natural immune system is that part of the immune system that we are born with. The innate immune system keeps out invading organisms (pathogens) such as viruses, bacteria and fungii via a number of mechanisms. These include

• physical barriers such as the skin, the blood-brain-barrier and mucous layers;
• mechanisms such as fever to overheat the invaders.
• pathogen destroying enzymes secreted in mucous layers and elsewhere;
• the complement - a system of plasma proteins that principally attack bacteria;
• the inflammatory response which involves the action of several biochemicals including histamines, kinins, cytokines, chemokines, neutrophils and mast cells among others, which destroy pathogens, ready cells to resist attack and regulate other parts of the immune response.
• non-specific white blood cells called effector cells, principally the macrophages which gobble up pathogens;

Innate immunity is always present in the body and can react very quickly to an infection. The fact that it is non-specific allows it to target most invaders without previously having come across them.

The division between the innate and acquired immune systems is far from complete and there are several interactions and feedback mechanisms in operation between the two. These include cytokine secretion, antigen presentation and cell-to-cell communication.

Innate Immunity Links:

Innate (non-specific) Immunity
Non Specific "Innate" Immunity
Innate Human Immunity
Interrelationship between innate & acquired immunity
Innate versus adaptive immunity

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