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Human Immune System
The human immune system is a combination of biological structures, that include cells,
tissues and organs (and their combined networks) as well as processes (both physical and
chemical) that constitute our protection against pathogens (and disease). Ours is a rather complex
system, distinguished by its effectivity against a wide range of threats: bacteria, viruses (quite
primitive), parasitic worms and other microbes. Another aspect that distinguishes our system is
the adaptability, which measures the learning ability of our immune system from past
experiences, exposures and diseases. It is our immunological memory resulting in acquired
immunity that allows us to benefit from vaccinations.
Precise Working
The human defense system is setup in layers, which improve in specificity. At its
outermost, the system comprises of physical barriers, for example, the skin, which prevents
pathogens from gaining entry into the human body. Ear wax, nose hair, mucus secretions etc are
examples of other physical barriers. Where barriers cannot be effective, the body has other
mechanisms. For example to keep pathogens out of the lungs, the body has evolved mechanisms
of coughing or sneezing. Likewise, the flushing action of urine and tears enables the removal of
pathogens from bodily tracts (Klosterman, 2008).
Chemical barriers like the antimicrobial peptides and beta-defensins, enzymes found in
the saliva and breast milk are all anti-bacterials as well, aiming to boost defenses. Vaginal
secretions may get slightly acidic while semen may contain zinc and other defensins to protect
against pathogens. While these measures may not eliminate the invaders, the harsh pH levels
certainly reduce their numbers, thereby decreasing their potency.
Inflammation occurs as an initial symptom of infection – seen as redness,
swelling, local hike in temperature and pain. These occur from the greater blood flowing into the
region and the release of eicosanoids that result in fever. Interleukins, chemokines and
interferons help attract white blood cells and have anti-viral effects by reducing or shutting down
protein synthesis in the affected cells.
Once these are breached, however, the pathogen must contend with the non-specific
reaction of the innate immune system; this response is not calibrated, maximum response occurs
as soon as exposure happens (via pattern recognition receptors). Vertebrates next present
pathogens with what is already discussed, the adaptive immune system. The triggers for the
adaptive reactions rest within the innate response. Adaptation and precision are used for greater
specificity here. The immune system also learns and retains information over the pathogen here.
This allows it to tweak its reaction for speed and accuracy in the future. There is also a specific
lag time between exposure and maximum response at this stage. Both the stages above, however,
have cell-mediated as well as humoral components. It should be noted that the human immune
system is only as effective as its ability to make out the difference between native and alien
molecules. The precise methodology involves a class of non-self molecules, known as antigens,
binding to immune receptors that triggers a response.
The Immune System & The Nervous System
Research is starting to confirm what scientists have known for long. There are intricate
connections between all of the body’s systems. The immune system and the nervous system are
most predominantly seen linked via the adrenal glands. When the body is dealing with external
stress, the actions of the immune system to any infections or pathogens may be seen to have a
retarding effect. For example, during a situation of “flight”, we will perform better if the
temperature of body was normal. Once the brain pips the adrenal gland to release stress
hormones into the blood, these hormones enable us to tap into extra reserves of energy for
immediate usage. The hormones additionally also subdue any immune reactions of antibodies or
Other links between the immune system and the nervous system come from hormones
and chemicals that transmit messages between nerve receptors – these also communicate with
certain immune cells. Lymphokines have long been suspected to transmit messages to the
nervous system. Lymphoid organs have also been found connected with nerve fibers, suggesting
that the brain also talks to the nervous system indirectly via nerve cells.
The Immune System, The Digestive System and The Reproductive System
There are strong linkages between the innate immune system and the reproductive
system. In females, the endocrine system regulates the immune system’s interaction within the
reproductive realm: the reproductive tracts and the other mucosal surfaces. Regulation also
extends to the gastrointestinal tracts and the urinary tracts. Very specific reactions (catalyzed and
regulated via the T-cells and the antibodies) are required from the adaptive side because sperm
as an antigen and the natural bacteria in the vagina must be distinguished from pathogens that
enter from time to time. Germline encoded receptors on the other hand are used by the innate
system, in a rapid form of bombardment upon exposure. Vaginal secretions may become acidic
in order to prevent the pathogens from multiplying and gradually die. Likewise, there are present
several kinds of defensins (including zinc) in semen to kill pathogens that are exposed to it. The
gastrointestinal tracts use mucus to capture any microorganisms that may be present, while the
urinary tracts use urine as a natural flush against invading pathogens. Therefore the normal
working of the immune system is of major importance for all the other major systems in the
Problems with the Immune Function
There are three major failures that occur with the immune function: immunodeficiencies,
autoimmunity and hypersensitivities. Immunodeficiencies are related with the inactivity of the
immune system. Immunosenescence begins at around age 50 and progressively gets worse,
characterized by declining responses (Aw, Silva & Palmer, 2007). Obesity and alcoholism are
linked to an early onset and a graver impact of immunosenescence. Malnutrition also has a
contributing role in poorer regions of the world, specially deficiency of protein which influences
cell-mediated immunity. Antibody concentrations are reduced and cytokine production is
inhibited. Likewise removal of the thymus can leave a patient very susceptible to infections.
Acquired immunodeficiency involves conditions like the chronic granulomatous disease and
Autoimmune disorders are ones where we see overactive immune systems, at the other
end of the spectrum. There may be reduced ability to distinguish the non-self from the self parts
and as a result, the immune system sometimes attacks the self parts. Self peptides may be
targeted; examples of such autoimmune disorders include psoriasis, rheumatoid arthritis etc.
Finally, hypersensitive disorders are characterized by the immune system damaging the
native tissues. Here, symptoms may go from being mildly affected with an allergy, to needing
immediate medical help or even death. These disorders are divided into four types. The first
involves an allergic or an anaphylactic reaction. The second is where antibodies take to antigens
on the host cells – creating targets for immune responses. Type III hypersensitivity occurs when
immune complexes are found in host tissues, while Type IV hypersensitivity is slower, takes a
few days to develop and are mediated by T-cells. Example includes “contact dermatitis”
(Ghaffar, 2006).

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