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Immune system

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The immune system is a system of biological structures and processes within an organism that protects against disease.

To function properly, an immune system must detect a wide variety of agents, known as pathogens, from viruses to parasitic worms, and distinguish them from the organism's own healthy tissue. In many species, the immune system can be classified into subsystems, such as the innate immune system versus the adaptive immune system, or humoral immunity versus cell-mediated immunity.

Pathogens can rapidly evolve and adapt, and thereby avoid detection and neutralization by the immune system; however, multiple defense mechanisms have also evolved to recognize and neutralize pathogens. Even simple unicellular organisms such as bacteria possess a rudimentary immune system, in the form of enzymes that protect against bacteriophage infections. Other basic immune mechanisms evolved in ancient eukaryotes and remain in their modern descendants, such as plants and insects. These mechanisms include phagocytosis, antimicrobial peptides called defensins, and the complement system. Jawed vertebrates, including humans, have even more sophisticated defense mechanisms,[1] including the ability to adapt over time to recognize specific pathogens more efficiently. Adaptive (or acquired) immunity creates immunological memory after an initial response to a specific pathogen, leading to an enhanced response to subsequent encounters with that same pathogen. This process of acquired immunity is the basis of vaccination.

Disorders of the immune system can result in autoimmune diseases, inflammatory diseases and cancer.[2][3] Immunodeficiency occurs when the immune system is less active than normal, resulting in recurring and life-threatening infections. In humans, immunodeficiency can either be the result of a genetic disease such as severe combined immunodeficiency, acquired conditions such as HIV/AIDS, or the use of immunosuppressive medication. In contrast, autoimmunity results from a hyperactive immune system attacking normal tissues as if they were foreign organisms. Common autoimmune diseases include Hashimoto's thyroiditis, rheumatoid arthritis, diabetes mellitus type 1, and systemic lupus erythematosus.

Immune system. The immune system is a system of biological structures and processes within an organism that protects against disease.

Immune system

To function properly, an immune system must detect a wide variety of agents, known as pathogens, from viruses to parasitic worms, and distinguish them from the organism's own healthy tissue.

History of Immunology

Layered defense. Innate immune system. Adaptive immune system. Diseases and Disorders of the Immune system. Other mechanisms and evolution. Cancer immunology. Cancer immunology is a branch of immunology that studies interactions between the immune system and cancer cells (also called tumors or malignancies).

Cancer immunology

It is a growing field of research that aims to discover innovative cancer immunotherapies to treat and retard progression of the disease. The immune response, including the recognition of cancer-specific antigens, is of particular interest in the field as knowledge gained drives the development of targeted therapy (such as new vaccines and antibody therapies) and tumor marker-based diagnostic tests.[1][2] For instance in 2007, Ohtani published a paper finding tumour infiltrating lymphocytes to be quite significant in human colorectal cancer.[3] The host was given a better chance at survival if the cancer tissue showed infiltration of inflammatory cells, in particular those prompting lymphocytic reactions.

The results yielded suggest some extent of anti-tumour immunity is present in colorectal cancers in humans.

Physiological regulation

Manipulation in Medicine. Predicting Immunogenicity. Manipulation by pathogens. Clonal selection. Clonal selection of lymphocytes: 1) A hematopoietic stem cell undergoes differentiation and genetic rearrangement to produce 2) immature lymphocytes with many different antigen receptors.

Clonal selection

Those that bind to 3) antigens from the body's own tissues are destroyed, while the rest mature into 4) inactive lymphocytes. Most of these will never encounter a matching 5) foreign antigen, but those that do are activated and produce 6) many clones of themselves. Hapten. A hapten is a small molecule that can elicit an immune response only when attached to a large carrier such as a protein; the carrier may be one that also does not elicit an immune response by itself.


(In general, only large molecules, infectious agents, or insoluble foreign matter can elicit an immune response in the body.) Once the body has generated antibodies to a hapten-carrier adduct, the small-molecule hapten may also be able to bind to the antibody, but it will usually not initiate an immune response; usually only the hapten-carrier adduct can do this. Sometimes the small-molecule hapten can even block immune response to the hapten-carrier adduct by preventing the adduct from binding to the antibody, a process called hapten inhibition. Immune network theory. The immune network theory is a theory of how the adaptive immune system works, that has been developed since 1974 mainly by Niels Jerne[1] and Geoffrey W.

Immune network theory

Hoffmann.[2][3] The theory states that the immune system is an interacting network of lymphocytes and molecules that have variable (V) regions. These V regions bind not only to things that are foreign to the vertebrate, but also to other V regions within the system. The immune system is therefore seen as a network, with the components connected to each other by V-V interactions. Immune network theory has also inspired a subfield of optimization algorithms similar to artificial neural networks, and unrelated to biological immunology.[12] Immune receptor. Types[edit] The main receptors in the immune system are pattern recognition receptors (PRRs), Toll-like receptors (TLRs), killer activated and killer inhibitor receptors (KARs and KIRs), complement receptors, Fc receptors, B cell receptors and T cell receptors.[1] See also[edit] antigen References[edit] ^ Jump up to: a b c Lippincott's Illustrated Reviews: Immunology.

Immune receptor

External links[edit] immunologic receptor at the US National Library of Medicine Medical Subject Headings (MeSH) Mucosal immunology. Vaccine-naive. The time-course of an immune response begins with the initial pathogen encounter, (or initial vaccination) and leads to the formation and maintenance of active immunological memory.


Effect on herd immunity[edit] Communicable diseases, such as measles and influenza, are more readily spread in vaccine-naïve populations, causing frequent outbreaks. Vaccine-naïve persons threaten what epidemiologists call herd immunity.[5][6][7] This is because vaccinations provide not just protection to the those who receive them, but also provide indirect protection to those who remain susceptible because of the reduced prevalence of infectious diseases. Fewer individuals available to transmit the disease, reduce the incidence of it, creating herd immunity.[8] See also[edit] References[edit] Jump up ^ Menson, E.

External links[edit] Polyclonal B cell response. Polyclonal response by B cells against linear epitopes[1] Examples of substances recognized as foreign (non-self) In the course of normal immune response, parts of pathogens (e.g. bacteria) are recognized by the immune system as foreign (non-self), and eliminated or effectively neutralized to reduce their potential damage.

Polyclonal B cell response

Such a recognizable substance is called an antigen. Original antigenic sin. The original antigenic sin: When the body first encounters an infection it produces effective antibodies against its dominant antigens and thus eliminates the infection.

Original antigenic sin

But when it encounters the same infection, at a later evolved stage, with a new dominant antigen, with the original antigen now being recessive, the immune system will still produce the former antibodies against this old " now recessive antigen" and not develop new antibodies against the new dominant one, this results in the production of ineffective antibodies and thus a weak immunity. This phenomenon was first described in 1960 by Thomas Francis, Jr. in the article "On the Doctrine of Original Antigenic Sin".[3][4] It is named by analogy to the theological concept of original sin.

According to Thomas Francis, who originally described the idea, [3] and cited by Richard Krause:[4] Immunostimulant. Immunostimulants, also known as immunostimulators, are substances (drugs and nutrients) that stimulate the immune system by inducing activation or increasing activity of any of its components.


One notable example is the granulocyte macrophage colony-stimulating factor. Classification[edit] There are two main categories of immunostimulants:[1] Immunoproteomics. Immunoproteomics is the study of large sets of proteins (proteomics) involved in the immune response. Examples of common applications of immunoproteomics include: the isolation and mass spectrometric identification of MHC (major histocompatibility complex) binding peptidespurification and identification of protein antigens binding specific antibodies (or other affinity reagents), andcomparative immunoproteomics to identify proteins and pathways modulated by a specific infectious organism, disease or toxin. An important aspect to proteomics in general is that mass spectrometry is the ultimate technique used for protein identification.

Purcell, A. W.; J.