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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:

Also called immune deficiency, this is where the immune system's ability to fight infectious disease is compromised, inadequate, or entirely absent.
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.