Immunology is a broad branch of biomedical science that covers study of all aspects of the immune system in all organisms. It deals with, among other things, the physiological functioning of the immune system in states of both health and disease; malfunctions of the immune system in immunological disorders (autoimmune diseases, hypersensitivities, immune deficiency, allograph rejection); the physical characteristics of organs in the immune system; and in vitro, in vivo and in situ chemical and physiological properties of biological components of the immune system. Immunology has various applications in several disciplines of science, and as such is further categorised accordingly.

Contents

1 Histological examination of the immune system 2 Classical immunology 3 Clinical immunology 4 Immunotherapy 5 Diagnostic immunology 6 Evolutionary immunology 7 See Also 8 References

Histological examination of the immune system

Before even the concept of immunity was developed numerous early physicians characterised organs that would later prove to be part of the immune system. The key organs of the immune system are the thymus, spleen, bone marrow lymph nodes (including major lymph nodes such as tonsils, and adenoids), lymph vessels and various tissue associated lymphoid tissues. The major organs, the thymus and spleen, are really only histologically examined post-mortem during autopsy. However some lymph nodes, and accessory lymphid tissue can be surgically excised for examination while patients are still alive.

Many components of the immune system are actually cellular in nature and not associated with any specific organ, but imbedded or circulating in various tissues located about the body.

Classical immunology

Classical immunology ties in with the fields of epidemiology and medicine. It studies the relationship between the body's systems, pathogens and immunity. The earliest written mention of immunity can be traced back to the plague of Athens in 430 BC. Thucydides noted that people who had recovered from a previous bout of the disease could nurse the sick without coming down with the illness a second time. Many other ancient societies have references to this phenomenom but it was not until the 19th and 20th centuries before the concept developed into scientic theory.

The study of the cellular and molecular components that comprise the immune system, including their function and interaction is the central science of immunology. The immune system has been divided into innate immune responses, and adaptive immune responses, the latter of which is further divided into humoral and cellular components.

The mainstay of classical immunology has been the interaction between antibodies and antigens. Without an understanding of the properties of these two biological entities, much of immunology would be non-existent.

In the 21st century though, immunology has broadened its horizons with much reserach being performed into more specialised niches of immunology. This includes the immunological function of cells, organs and systems not normally associated with immunology, as well as the function of the immune system outside of clasiscal models of immunity.

Clinical immunology

Clinical immunology is the study of diseases caused by the immune system and diseases of the immune system from a medical perspective.

Many diseases caused by the immune system fall into two broad categories: immunodeficiency, in which parts of the immune system fail to provide an adequate response (examples include chronic granulomatous disease), and autoimmunity, in which the immune system attacks the body (examples include lupus and rhumetoid arthritis). Other immune system disorders include hypersensitivities, in which the system responds inappropriately to harmless compounds (asthma and allergies).

The most well-known disease that affects the immune system itself is HIV, the virus which causes AIDS. AIDS is an immunodeficiency characterized by the lack of CD4+ ("helper") T cells, which are destroyed by the HIV virus.

Clinical immunologists also study ways to prevent transplant rejection, in which the immune system attempts to destroy allografts or xenografts.

Immunotherapy

See main article Immunotherapy

The use of immune system components to treat a disease or disorder is known as immunotherapy. Immunotherapy is most commonly used in the context of the treatment of cancers as an adjuvant to chemotherapy (drugs) and radiotherapy (radiation). However, immunotherapy is often used in the immunosuppressed (such as HIV patients) and people suffering from other immune deficiencies.

Immunotherapy has also been successful in the alleviation of allergies.

Diagnostic immunology

The specificity of the bond between antibody and antigen has made it an excellent tool in the detection of substances in a variety of diagnostic techniques. Antibodies specific to a desired analyte can be conjugated with a radiolabel, fluorescent label, or color-forming enzyme and used as a "probe" to detect the analyte.

Well known applications of this include immunoblotting, ELISA and immunohistochemical staining of microscope slides. The speed, accuracy and simplicity of such tests has led to the development of rapid techniques for the diagnosis of disease, microbes and even illegal drugs in the nevironment as opposed to in the laboratory (of course tests conducted in closed environmnet have a higher degree of accuracy). Such testing is also used to distinguish compatible blood types.

Evolutionary immunology

Study of the immune system in extant and extinct species is capable of giving us a key understanding of the evolution of species on Earth.

A hierachy of immunity can be seen from simple phagocytotic protection from single celled organisms, to circulating antimicrobial peptides in insects to lymphoid organs in vertebrates. Of course, like much of evolutionary, this is often seen from an anthrocentric ("humans are best") model of evolution, but it must be recognised, that every organisms immune system is absolutely capable of protecting it from most forms of harm.

Insects and other arthropods, while not possessing true adaptive immunity, show highly evolved systems of innate immunity, and are additionally protected from external injury (and exposure to pathogens) by their chitinous shells.

See Also

• Immune system
• autoimmunity

References

Goldsby RA, Kindt TK, Osborne BA and Kuby J (2003) Immunology, 5th Edition, W.H. Freeman and Company, New York, New York, ISBN 0-7167-4947-5

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