The immune system can detect and identify many different kinds of disease agents. Examples are viruses, bacteria and parasites. The immune system can detect a difference between the body's own healthy cells or tissues, and 'foreign' cells. Detecting an unhealthy intruder is complicated, because intruders can evolve and adapt so that the immune system will no longer detect them.
Innate immune system [change]
Even simple unicellular organisms such as bacteria possess enzyme systems that protect against viral infections. Other basic immune mechanisms appeared in ancient life forms and remain in their modern descendants, such as plants and insects. These mechanisms include antimicrobial peptides (called defensins), phagocytosis, and the complement system. These are the innate immune system, which defends the host from infections in a non-specific way. The simplest innate system is the cell wall or barrier on the outside to stop intruders getting in. For example, skin stops most outside bacteria getting in.
Adaptive immune system [change]
Vertebrates, including humans, have much more sophisticated defense mechanisms. Whereas the innate immune system is found in all metazoa, the adaptive immune system is only found in vertebrates. It is thought to have arisen in the first jawed vertebrates.
The adaptive immune response gives the vertebrate immune system the ability to recognize and remember specific pathogens. The system mounts stronger attacks each time the pathogen is encountered. It is adaptive immunity because the body's immune system prepares itself for future challenges.
The typical vertebrate immune system consists of many types of proteins, cells, organs, and tissues that interact in a complex and ever-changing network. This acquired immunity creates a kind of "immunological memory".
The process of acquired immunity is the basis of vaccination. Primary response can take 2 days to 2 weeks to develop. After the body gains immunity towards a certain pathogen, if infection by that pathogen occurs again, the immune response is called the secondary response.
Autoimmune disorders [change]
In some organisms, the immune system has its own problems within itself, called disorders. These result in other diseases, including autoimmune diseases, inflammatory diseases and possibly even cancer. Immunodeficiency diseases occur when the immune system is less active than normal. Immunodeficiency can either be the result of a genetic (inherited) disease, or an infection, such as the acquired immune deficiency syndrome (AIDS), that is caused by the retrovirus HIV, or other causes.
In contrast, autoimmune diseases result from an immune system that attacks normal tissues as if they were foreign organisms. Common autoimmune diseases include Hashimoto's thyroiditis, rheumatoid arthritis, diabetes mellitus type 1, and lupus erythematosus.
History of immunology [change]
Immunology is a science that examines the structure and function of the immune system. It 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. Thucydides (460–395 BC) noted that people who had recovered from a previous bout of some diseases 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 led to Louis Pasteur (1822–1895) developing vaccination and the germ theory of disease. Pasteur's theory was in direct opposition to contemporary theories of disease, such as the miasma theory. It was not until the proofs Robert Koch (1843–1910) published in 1891 (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, when the yellow fever virus was discovered by Walter Reed (1851–1902).
Immunology made a great advance 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 (1854–1915), who proposed the side-chain theory to explain the specificity of the antigen-antibody reaction. The Nobel Prize for 1908 was jointly awarded to Ehrlich and the founder of cellular immunology, Ilya Mechnikov (1845–1916).
- "Genomic analysis of plants and animals provides evidence that a sophisticated mechanism of host defense was in existence by the time the ancestors of plants and animals diverged. This system, shared by plants and animals, is the Toll pathway of NFκB activation of gene function... The necessary DNA sequences are found in invertebrates, vertebrates, and plants". Janeway.
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- The Nobel Prize in Physiology or Medicine 1905, Nobelprize.org, accessed 8 January 2007
- Major Walter Reed, U.S. Army, Walter Reed Army Medical Center, accessed 8 January 2007.
- In humoral immunity, antibodies are secreted into bodily fluids such as blood and lymph.
- Mechnikov, Ilya; translated by F.G. Binnie (1905) (full text version: Google Books). Immunity in infective diseases. Cambridge University Press. ISBN 0548-64719-4. http://books.google.com/?id=ywKp9YhK5t0C&printsec=titlepage&vq=Ehrlich&dq=history+of+humoral+immunity.
- The Nobel Prize in Physiology or Medicine 1908 Nobelprize.org, accessed 8 January 2007