The immune system hasdifferent defense mechanisms including theinflammatory system, surface barriers, complement system, cellular barriers andnatural killer cells. These defense mechanisms are all apart of the innateimmune system. “The innate immune system includes primary deterrents that help itbe a non-specific response system. These deterrents ensure protection againstforeign invaders” (Bailey). “Six key components of theimmune system can be found circulating in the blood in some form.

Three of themare different kinds of cells, and three are soluble proteins” (Funk &Wagnalls). The surface barriers protectorganisms from infection. The chemicalbarrier, the biological barrier andthe mechanical barrier. Examples ofthe mechanical barrier are human skin, the exoskeleton of insects and thecuticle of most leaves. Chemical barriers also protect against infection, suchas gastric acid and proteases which are in the stomach. They defend the body against ingested pathogens. “Commensal floraserves as biological barriers by competing with pathogenic bacteria for foodand space and, in some cases, by changing the conditions in their environment, suchas pH or available iron” (Anonymous). The surface barrier system can fail when the skin breaks.

Organismscannot be completely sealed off from their surrounding environments, which iswhy they have other defense mechanisms.The complement systemis up next. This system, which is a biochemical cascade, attacks the surface offoreign invaders. “It contains over 30 different proteins and is named for itsability to “complement” the killing of pathogens by antibodies” (Smitha).Many species that have complement systems, including humans and mammals, even someinvertebrates have a complement system.

Plants and fish can also have a complementsystem. “In humans, the response is activated one of two ways. Either by complementbinding to antibodies that have attached to these microbes or the binding ofcomplement proteins to carbohydrates on the surfaces of microbes” (Anonymous).

The cells of theimmune system are known as white blood cells. Cellular barriers which includewhite blood cells, also known as leukocytes, is the second stage of the innateimmune system, acting as single-cell organisms. B cells, also known as Blymphocytes, are a type of white blood cell. “B cells positively regulateimmune responses through antibody production and optimal CD4(+) T-cellactivation. However, a specific and functionally important subset of B cellscan also negatively regulate immune responses in mouse autoimmunity andinflammation models” (Anonymous). T cells, or otherwise known as T lymphocytes,are another type of white blood cell. The T cell category is a broad one thatincludes various types of T cells that respond to a stimulus. There are, however,two main types of T cells.

These are known as cytotoxic T cells and helper T cells. “Effector cytotoxic T cellsdirectly kill cells that are infected with a virus or some other intracellularpathogen. Effector helper T cells, by contrast, help stimulate the responses ofother cells—mainly macrophages, B cells, and cytotoxic T cells” (Alberts). The natural killer cells do not directlyattack the invader, they target and destroy the compromised host cell.

Naturalkiller cells, or NK cells, are a type of cytotoxic lymphocyte critical to theinnate immune system (Anonymous). NKCells are not apart of the T lymphocyte family. The NK cells provide a rapidresponse to the cells that are infected, acting around three days after theinfection. “They have the ability to recognize stressed cells in the absence of antibodies and MHC” (Anonymous). Thatability allows them to have a much faster reaction time. The cell receptors ofNK can be distinguished by function. Activation receptors andInhibitory receptors are the types of the NK cell receptors.

There is one more type of defense mechanism in the innate immunesystem, and it is believed to be the most important one.One type of deterrentsis inflammatory reaction (initiated by immune cells) (Bailey). The inflammatorydefense is the body’s first line of defense, without it we would be at themercy of infection (Williams 28-32). “There’s no question, inflammation is everything,” saysCharles Serhan, an immunologist at Harvard Medical School. “In thepost-genomic era, understanding inflammation is the next frontier.”(Williams 28-32).

While the inflammatory system helps protect from infection italso helps with injuries. When you get injured or infected the inflammatoryresponse brings redness, swelling, heat and pain to that specific area. If youcut yourself, the body sends in microbe-fighting molecules (including oxidants)which is why the wound gets red, hot and swollen (Underwood 26-28). There is also anothertype of immune system called the adaptive immune system, which works slowerthan the innate immune system. It also works in a more specific way.  There are two parts to the adaptive immunesystem, passive and active: – Passive immunity canoccur naturally, the antibodies are transferred from the mother to the fetusthrough the placenta and it can also occur artificially, when high levels ofantibodies are transferred to someone through blood products that contain theantibodies.

– Active immunityinvolves two types of white blood cells – T-cells and B-cells. Dendritic cells,after they have eaten and digested the pathogen, present the pathogen pieces toT-cells, which then activates the T-cells (Reed).The cells in the humanbody have a range of different type of defense mechanisms in them. The immunesystem is also known as the specific defense mechanism that is used to fightagainst foreign invaders. There are also nonspecific defense mechanisms used aswell. Some of the nonspecific defense mechanisms include fever and interferon. “The fever is considered a nonspecificdefense mechanism because it develops in response to numerous traumas.

Theinterferon is a group of antiviralsubstances produced by body cells in response to the presence of viruses”(Anonymous). To recap, there arefive different types of defense mechanisms in the innate immune system. Thesefive types include inflammatory system, surface barriers, complement system,cellular barriers and natural killer cells. They all have their specific rolesthat are vital to the protection of human cells. There are two different typesof the adaptive immune system, passive immunity and active immunity. Both ofthese types of immune systems, innate and adaptive, help tremendously to fightoff foreign invaders and protect our cells.