The Workings Of The Immune System
Our immune system is composed of active immunity, acquired through normal
infestation of intestinal and respiratory systems after birth, and passive
immunity, generally consisting of antibodies acquired from maternal blood
and breast milk.
The human immune system is further characterized as having specific
responses, such as the production by the body of specific antibodies to
counter specific foreign proteins or antigens, and non-specific responses,
which consist of the general systemic response to undesirable substances.
Included in the general repertoire of non-specific response is the skin,
the
mucous membranes of the respiratory and digestive tracts, reflex actions
of
sneezing and coughing, natural antibodies, complement proteins,
interferon,
the process of phagocytosis (cells devouring other cells), the effect of
fatty acids, inflammatory response, the action of reticulo-endothelial
cells, the action of lysozyme and other enzymes, the response of
respiratory
and intestinal celia, the effect of stomach acid on bacteria, and
secretions
that contain antibodies themselves, such as secretory immunoglobulin,
which
assists the process of phagocytosis - an example being the action of white
blood cells on pathogenic organisms.
The human body maintains several lines of defense against the invasion of
foreign proteins and subsequently produced toxins. The first line of
defense
is the skin, which is primarily composed of a protein-based material
called
keratin. The skin also secretes various oils, fatty acids and lactic acids
which inhibit the general growth of bacteria, although many body flora
that
inhabit both the skin and the interior of the body are relatively
innocuous,
given that the immune system is in a normal condition, and many body
processes are assisted by their existence.
These organisms that exist in symbiosis with human anatomy are sensitive
to
antibiotics and synthetic materials administered by current medical
practice. Disturbance of the delicate balance can lead to overpopulation
of
pathogenic organisms. The proliferation of yeast infections caused by
administration of commercial antibiotic drugs is an example, as is the
diarrhea and bleeding caused by obliteration of intestinal flora by
antibiotics. Since the maintenance of internal organisms is an essential
part of the human immune response, the death of these organisms weakens
the
overall immune system capability.
The white cells in the body, the leukocytes, are generally divided into
two
groups, the granulocytes, which include neutrophils, eosinophils and
basophils, and the non-granulated lymphocytes and monocytes. Neutrophils
constitute the most prevalent type of granulocyte, and have a nucleus
containing a number of lobes. Because of the segmented nature of the
nucleus, neutrophils are also called polymorphonuclear leukocytes. They
have
an interesting property in that they have the ability to form physical
barriers against pathogenic organisms. The eosiniphil comprises about 2%
of
the leukocytes in the bloodstream, and appear to be connected with defense
against parasitic infection and allergic response, rather than against
microorganisms and toxins. Basophils also have a role to play in allergic
response, and contain histamin and heparin. A further form of the
leukocyte
is the monocyte, which has the capacity to ingest foreign particles and
bacteria. The monocyte appears to be active in conditions presented by
tuberculosis and fungal infections.
Another natural line of defense is the lymphatic system. Most cellular
structures in the body are bathed in lymph, a clear fluid which acts as a
general dumping ground for unwanted substances, later filtered out through
the liver and kidneys. The lymph moves through a series of ducts and
glands
by virtue of a specialized series of muscular contractions, many of which
are generated during the act of physical exercise. It is the lymphatic
system which contains the aforementioned reticulo-endothelial cells which
trap and ingest various organisms within the lymph. These cells also form
the lining of several im****tant organs, and are also present within the
liver and spleen. When a foreign protein structure is located, connective
tissue traps the foreign structure and lymphocytes are dispersed to engulf
the offending organism.
In the circulatory system are macrophages, specialized white blood cells
that ingest and disrupt organisms found in the blood. After macrophages
perform this action, processed antigens appear on the surface of the
macrophages membrane. It is these processed antigens leftover from the
destruction of organisms that are sensed by the T-cell lymphocytes,
prompting them to send out substances called lymphokines, which in turn
alert B-cell lymphocytes to produce an antibody in response to the
processed
antigen, otherwise taken as a processed foreign protein. Each B-lymphocyte
has approximately 100,000 immunoglobulins on its surface.
Antibodies produced by the B-cells are sometimes called immunoglobulins,
designated by the symbol Ig, and are released as the B-cell is stimulated
by
the presence of foreign antigens to transform into a plasma cell which
manufactures the specific antibody required for the foreign antigen. There
are generally five types of immunoglobulins. The first antibody, IgM,
reproduced in response to a foreign antigen is a large molecule found
typically in the blood which stimulates the process of phagocytosis. The
process of passive immunity involving maternal blood given to the fetus
involves the antibody IgG, which is responsible for activating the
macrophages. It can directly destroy many antigens on contact, and is the
most abundant immunoglobulin in the body. Membranes in the respiratory
tract, urinary tract and intestines produce IgA, which is produced
directly
at the site of an attack on a membrane by a foreign antigen. When the
human
body is experiencing an allergic reaction, IgE is released. The last
immunoglobin identified, IgD, is not well understood, and is found in
minimal quantities in the blood, as well as on the surface of B-cell
lymphocyte membranes.
Another line of defense involves complements, substances manufactured in
the
linings of the intestines, the liver, spleen and macrophages. The main
substance is known as properdin, and its function is the neutralization of
viruses and bacteria.
The reticulo-endothelial cells mentioned earlier comprise another line of
defense known as the reticulo-endothelial system, and produce specific
substances involved in phsiological defense, primarily proteases, which
play
a role in detoxification of harmful substances.
In addition to the immunological defense system mentioned above, the body
maintains a chemical defense system. The blood itself, by virtue of its
chemistry, is to a great degree bacteriostatic and virucidal, but this
depends very heavily on correct nutrition which produces optimum levels of
vitamin C and vitamin B6 (pyridoxine), in addition to other substances. In
fact, the optimum response of the immune system is said to depend heavily
upon adequate levels of vitamins.
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