The system can be found circulating in

The immune system has
different defense mechanisms including the
inflammatory system, surface barriers, complement system, cellular barriers and
natural killer cells. These defense mechanisms are all apart of the innate
immune system. “The innate immune system includes primary deterrents that help it
be a non-specific response system. These deterrents ensure protection against
foreign invaders” (Bailey). “Six key components of the
immune system can be found circulating in the blood in some form. Three of them
are different kinds of cells, and three are soluble proteins” (Funk &

The surface barriers protect
organisms from infection. The chemical
barrier, the biological barrier and
the mechanical barrier. Examples of
the mechanical barrier are human skin, the exoskeleton of insects and the
cuticle of most leaves. Chemical barriers also protect against infection, such
as gastric acid and proteases which are in the stomach. They defend the body against ingested pathogens. “Commensal flora
serves as biological barriers by competing with pathogenic bacteria for food
and space and, in some cases, by changing the conditions in their environment, such
as pH or available iron” (Anonymous). The surface barrier system can fail when the skin breaks. Organisms
cannot be completely sealed off from their surrounding environments, which is
why they have other defense mechanisms.

The complement system
is up next. This system, which is a biochemical cascade, attacks the surface of
foreign invaders. “It contains over 30 different proteins and is named for its
ability to “complement” the killing of pathogens by antibodies” (Smitha).
Many species that have complement systems, including humans and mammals, even some
invertebrates have a complement system. Plants and fish can also have a complement
system. “In humans, the response is activated one of two ways. Either by complement
binding to antibodies that have attached to these microbes or the binding of
complement proteins to carbohydrates on the surfaces of microbes” (Anonymous).

The cells of the
immune system are known as white blood cells. Cellular barriers which include
white blood cells, also known as leukocytes, is the second stage of the innate
immune system, acting as single-cell organisms. B cells, also known as B
lymphocytes, are a type of white blood cell. “B cells positively regulate
immune responses through antibody production and optimal CD4(+) T-cell
activation. However, a specific and functionally important subset of B cells
can also negatively regulate immune responses in mouse autoimmunity and
inflammation 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 that
includes 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 cells
directly kill cells that are infected with a virus or some other intracellular
pathogen. Effector helper T cells, by contrast, help stimulate the responses of
other cells—mainly macrophages, B cells, and cytotoxic T cells” (Alberts).

 The natural killer cells do not directly
attack the invader, they target and destroy the compromised host cell. Natural
killer cells, or NK cells, are a type of cytotoxic lymphocyte critical to the
innate immune system (Anonymous). NK
Cells are not apart of the T lymphocyte family. The NK cells provide a rapid
response to the cells that are infected, acting around three days after the
infection. “They have the ability to recognize stressed cells in the absence of antibodies and MHC” (Anonymous). That
ability allows them to have a much faster reaction time. The cell receptors of
NK can be distinguished by function. Activation receptors and
Inhibitory receptors are the types of the NK cell receptors. There is one more type of defense mechanism in the innate immune
system, and it is believed to be the most important one.

One type of deterrents
is inflammatory reaction (initiated by immune cells) (Bailey). The inflammatory
defense is the body’s first line of defense, without it we would be at the
mercy of infection (Williams 28-32). “There’s no question, inflammation is everything,” says
Charles Serhan, an immunologist at Harvard Medical School. “In the
post-genomic era, understanding inflammation is the next frontier.”
(Williams 28-32). While the inflammatory system helps protect from infection it
also helps with injuries. When you get injured or infected the inflammatory
response brings redness, swelling, heat and pain to that specific area. If you
cut 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 another
type of immune system called the adaptive immune system, which works slower
than the innate immune system. It also works in a more specific way.  There are two parts to the adaptive immune
system, passive and active:

– Passive immunity can
occur naturally, the antibodies are transferred from the mother to the fetus
through the placenta and it can also occur artificially, when high levels of
antibodies are transferred to someone through blood products that contain the

– Active immunity
involves 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 to
T-cells, which then activates the T-cells (Reed).

The cells in the human
body have a range of different type of defense mechanisms in them. The immune
system is also known as the specific defense mechanism that is used to fight
against foreign invaders. There are also nonspecific defense mechanisms used as
well. Some of the nonspecific defense mechanisms include fever and interferon. “The fever is considered a nonspecific
defense mechanism because it develops in response to numerous traumas. The
interferon is a group of antiviral
substances produced by body cells in response to the presence of viruses”

To recap, there are
five different types of defense mechanisms in the innate immune system. These
five types include inflammatory system, surface barriers, complement system,
cellular barriers and natural killer cells. They all have their specific roles
that are vital to the protection of human cells. There are two different types
of the adaptive immune system, passive immunity and active immunity. Both of
these types of immune systems, innate and adaptive, help tremendously to fight
off foreign invaders and protect our cells.