The innate immune system gets its name from that fact that we are all born with it already in place, and it changes little throughout our lives. This division of the immune system provides protection by recognizing general features of possible pathogens. For instance, barriers such as the skin block entry of many kinds of organisms. Similarly, cells of the innate immune response recognize general features of pathogens, such as the cell walls of bacteria. These cells do not distinguish within the various classes of pathogens. To use a military analogy, it would be like using the same type of missile to shoot at many different kinds of targets instead of having different missiles for different types of target. Macrophages, for instance, are cells that participate in the innate immune response by finding, eating, and killing many different types of bacteria. Natural killer cells (NK cells) are another type of immune cell that functions to eliminate cells that have become infected with viruses and cancer cells.(1)
There are several different components of the innate immune system. While is it sometimes called 'non-specific' immunity, that is not really accurate. The defenses presented below are geared toward specific kinds of living and non-living 'invaders'. When an organisma or particle attempts to enter the body, there are several physical and chemical barriers that must be bypassed. Our skin is a tough flexible shield that blocks many types of invaders. The entry points to our body are protected by sticky mucus (i.e. mouth, nose, anus, vagina) or wax (ears) that traps bacteria, dust and other particles. Body secretions like the acid in our stomachs and proteins in saliva and tears also work to prevent entry. Our hair keeps larger organisms from reaching our skin. If an invading organism or particle (i.e. a thorn) do make it past these defenses, cells (produced in the bone marrow) like macrophages and neutrophils are waiting to attack the foreign object.
Roll your mouse over the graphic below to see some components of the innate immune system in humans.
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