Immunology is the study of a body's protection from foreign macromolecules or
invading organisms and its responses to them. These invaders include viruses,
bacteria, protozoa or even larger parasites. Typically immune responses are
developed against our own proteins (and other molecules) in autoimmunity and
against our own aberrant cells in tumor immunity; this can go astray as with
multiple sclerosis (MS).
This section takes a basic look at the role of immunology and the immune system,
along with current thinking into its impact upon MS. Most feel that MS is an
autoimmune disease in that the immune system begins the cycle of inflammation
and then neurodegeneration.
The first line of defense against foreign organisms are barrier tissues such as
the skin that stops the entry of organisms into our bodies. If, however, these
barrier layers are penetrated, the body contains cells that respond rapidly to
the presence of the invaders. These cells include macrophages and neutrophils
that engulf foreign organisms and kill them without the need for antibodies. An
immediate challenge also comes from soluble molecules that deprive the invading
organism of essential nutrients (such as iron) and from certain molecules that
are found on the surfaces of epithelia, in secretions (such as tears and saliva)
and in the blood stream. This form of immunity is the innate or non-specific
immune system that is continually ready to respond to invasion.
The second line of defense is the specific or adaptive immune system which may
take days to respond to a primary invasion (such as an infection by an organism
that has not been seen before). In the specific immune system, the production of
antibodies (soluble proteins that bind to foreign antigens) as well as
cell-mediated responses (specific cells recognize foreign pathogens) seek and
destroy the invaders. With viruses or tumors, this response is also vital to the
recognition and destruction of virally-infected or tumorigenic cells. The
response to a second round of infection is often more rapid than to the primary
infection because of the activation of memory B and T cells. The signals
involved may be proteins such as lymphokines which are produced by cells of the
lymphoid system, cytokines and chemokines that are produced by other cells in an
immune response, and which stimulate cells of the immune system.
The History of Immunology
Immunology is a science that examines the structure and function of the immune
system and originates from medicine and early studies on the causes of immunity
to disease. The earliest known mention of immunity was during the plague of
Athens in 430 BC by Thucydides. He was dubbed the father of "scientific history"
due to his strict standards of evidence-gathering and analysis in terms of cause
and effect without reference to intervention by the gods. He noted that people
who had recovered from a previous bout of the disease could nurse the sick
without contracting the illness a second time.
In the 18th century, Pierre-Louis Moreau de Maupertuis made experiments with
scorpion venom and observed that certain dogs and mice were immune to this
venom. This and other observations of acquired immunity were later exploited by
Louis Pasteur in his development of vaccination and his proposed germ theory of
disease. Pasteur's theory was in direct opposition to contemporary theories of
disease, such as the miasma theory. It wasn't until Robert Koch's 1891 proofs,
for which he was awarded a Nobel Prize in 1905, that microorganisms were
confirmed as the cause of infectious disease. Viruses were confirmed as human
pathogens in 1901, with the discovery of the yellow fever virus by Walter Reed.
Immunology advanced greatly towards the end of the 19th century, through rapid
developments in the study of humoral immunity and cellular immunity.
Particularly important was the work of Paul Ehrlich, who proposed the side-chain
theory to explain the specificity of the antigen-antibody reaction; his
contributions to the understanding of humoral immunity were recognized by the
award of a Nobel Prize in 1908, which was jointly awarded to the founder of
cellular immunology, Elie Metchnikoff.
Classical Immunology
Classical immunology links with the fields of epidemiology, infectious diseases
and medicine. It studies the relationship between the body systems, pathogens,
and immunity. As discussed earlier, in 430 B.C. Athens, Thucydides noted that
people who had recovered from a previous bout of the disease could nurse the
sick without contracting the illness a second time. Many other ancient societies
have references to this phenomenon, but it wasn't until the 19th and 20th
centuries before the concept developed into scientific theory.
The study of the molecular and cellular components that comprise the immune
system, including their function and interaction, is the central science of
immunology. The immune system has been divided into a more primitive innate
immune system, and acquired or adaptive immune system of vertebrates, the latter
of which is further divided into humoral and cellular components.
The humoral (antibody) response is defined as the interaction between antibodies
and antigens. Antibodies are specific proteins released from a certain class of
immune cells (B lymphocytes). Antigens are defined as anything that elicits
generation of antibodies, hence they are Antibody Generators. Immunology itself
rests on an understanding of the properties of these two biological entities.
However, equally important is the cellular response, which can not only kill
infected cells in its own right, but is also crucial in controlling the antibody
response. Basically both systems are highly interdependent.
Lately, immunology has broadened its horizons with much research being performed
in the more specialized niches of immunology. This includes the immunological
function of cells, organs and systems not normally associated with the immune
system, as well as the function of the immune system outside classical models of
immunity.
Clinical Immunology
Immunology began as a branch of microbiology. It was initially understood to be
related to infectious diseases alone. The study of infectious disease and the
body’s response to them has a major role for the development of immunology and
its study. This began with the concept of germ theory.
Clinical immunology is the study of diseases caused by disorders of the immune
system (failure, aberrant action, and malignant growth of the cellular elements
of the system). It also involves diseases of other systems, where immune
reactions play a part in the pathology and clinical features.
Diseases caused by disorders of the immune system fall into two broad
categories:
Immunodeficiency
Also called immune deficiency, this is where the immune system's ability to
fight infectious disease is compromised, inadequate, or entirely absent.
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Autoimmunity
Is the failure of an organism to recognize its own constituent parts as self,
which allows an immune response against its own cells and tissues. Any disease
that results from such a misdirected immune response is termed an autoimmune disease.
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