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In biology, immunity is the capability of multicellular organisms to resist harmful microorganisms. Immunity involves both specific and nonspecific components. The nonspecific components act as barriers or eliminators of a wide range of
pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a g ...
s irrespective of their antigenic make-up. Other components of the
immune system The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinte ...
adapt themselves to each new disease encountered and can generate pathogen-specific immunity. Immunity is a complex biological system that can recognize and tolerate whatever belongs to the self, and to recognize and reject what is foreign (non-self).


Innate and adaptive

Innate Immunity First off, the immune system is a system in the body of animals that enables animals to avoid or limit many infections caused by pathogens. Pathogens are disease causing agents, causing a wide range of illnesses. As for Diseases it's when structure of an organism is negatively affected other than external injury. Both diseases and pathogens affect the immune system causing illness to specific animals. Animals has a form of innate immunity. In invertebrates, they have Barrier defenses Phagocytosis and Antimicrobial peptides. As for Vertebrates they have Barrier defenses, phagocytosis, antimicrobial peptides, natural killer cells, antimicrobial proteins, and inflammatory response. Barrier Defenses Barrier Defenses include skin, mucous, lysozyme, and acidic pH in the stomach and on the skin. The barrier defense like the skin prevents pathogens from entering, not only that the skin is a physical barrier that secretes oil with a high pH. Other Physical barriers include eyelids, lashes, mucous, and a very acidic stomach. All these physical immune system help defend against pathogens that occur in everyday life. Phagocytosis Phagocytosis is a type of white blood cell that helps breaks down pathogenic bacteria in your body. The phagocytotic cell types are Neutrophils and Macrophages. Neutrophils circulate in the bloods and Macrophages is in the connective tissues which are big eaters. Natural Killer Cells Natural killer cells circulate in the blood. Natural Killer Cells detect against virus and cancer cells, Natural killer cells release chemical that leads to cell death, though this is only in vertebrates only. Maternal natural killer cells transfer anti-microbial peptide granulysin through a nanotube to kill an infection in the cell of a placenta. Natural killer cells can attack extracellular and intracellular pathogens, killing off pathogens that can create illnesses within the body. Antimicrobial Peptides Antimicrobial peptides kill pathogens, they disorder membranes. Some Antimicrobial peptides kill both bacteria and fungi. Not only that they can interfere with DNA and protein synthesis. In addition, antimicrobial peptides demonstrate to have a variety of functions for example clearance of infection and induce pro-inflammatory cytokine production. Inflammatory response Inflammatory response is a response where upon injury the specific place becomes inflamed and warm to the touch. The reason why the site of injury becomes red and warm is because of the blood vessel dilation, causing warming and redish color. The messengers are Cytokines and Histamines. Cytokines are produced by macrophages recruit neutrophils. Histamines are produced by mast cells triggering blood vessels dilation of capillaries. The
immune system The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinte ...
has innate and adaptive components. Innate immunity is present in all metazoans, while adaptive immunity only occurs in vertebrates. The innate component of the immunity system involves the recognition of certain foreign (non-self) molecules to generate one of two types of innate immune responses: inflammatory responses and phagocytosis. The adaptive component, on the other hand, involves more advanced lymphatic cells that can distinguish between specific "non-self" substances in the presence of "self". The reaction to foreign substances is etymologically described as inflammation while the non-reaction to self substances is described as immunity. The two components of the immune system create a dynamic biological environment where "health" can be seen as a physical state where the self is immunologically spared, and what is foreign is inflammatorily and immunologically eliminated. "Disease" can arise when what is foreign cannot be eliminated or what is self is not spared. Innate immunity, also known as native immunity, is a semi-specific and widely distributed form of immunity. It is defined as the first line of defense against pathogens, representing a critical systemic response to prevent infection and maintain homeostasis, contributing to the activation of an adaptive immune response. It does not adapt to specific external stimulus or a prior infection, but relies on genetically encoded recognition of particular patterns. Adaptive or acquired immunity is the active component of the host immune response, mediated by antigen-specific lymphocytes. Unlike the innate immunity, the acquired immunity is highly specific to a particular pathogen, including the development of immunological memory. Like the innate system, the acquired system includes both humoral immunity components and cell-mediated immunity components. Adaptive immunity can be acquired either 'naturally' (by infection) or 'artificially' (through deliberate actions such as vaccination). Adaptive immunity can also be classified as 'active' or 'passive'. Active immunity is acquired through the exposure to a pathogen, which triggers the production of antibodies by the immune system. Passive immunity is acquired through the transfer of antibodies or activated T-cells derived from an immune host either artificially or through the placenta; it is short-lived, requiring booster doses for continued immunity. The diagram below summarizes these divisions of immunity. Adaptive immunity recognizes more diverse patterns. Unlike innate immunity it is associated with memory of the pathogen.


History of theories

For thousands of years mankind has been intrigued with the causes of disease and the concept of immunity. The prehistoric view was that disease was caused by supernatural forces, and that illness was a form of theurgic punishment for "bad deeds" or "evil thoughts" visited upon the soul by the gods or by one's enemies. In Classical Greek times, Hippocrates, who is regarded as the Father of Medicine, diseases were attributed to an alteration or imbalance in one of the
four humors Humorism, the humoral theory, or humoralism, was a system of medicine detailing a supposed makeup and workings of the human body, adopted by Ancient Greek and Roman physicians and philosophers. Humorism began to fall out of favor in the 1850 ...
(blood, phlegm, yellow bile or black bile). The first written descriptions of the concept of immunity may have been made by the Athenian Thucydides who, in 430 BC, described that when the plague hit
Athens Athens ( ; el, Αθήνα, Athína ; grc, Ἀθῆναι, Athênai (pl.) ) is both the capital and largest city of Greece. With a population close to four million, it is also the seventh largest city in the European Union. Athens dominates a ...
: "the sick and the dying were tended by the pitying care of those who had recovered, because they knew the course of the disease and were themselves free from apprehensions. For no one was ever attacked a second time, or not with a fatal result". Active immunotherapy may have begun with Mithridates VI of Pontus (120-63 BC) who, to induce active immunity for snake venom, recommended using a method similar to modern
toxoid A toxoid is an inactivated toxin (usually an exotoxin) whose toxicity has been suppressed either by chemical (formalin) or heat treatment, while other properties, typically immunogenicity, are maintained. Toxins are secreted by bacteria, whereas ...
serum therapy, by drinking the blood of animals which fed on venomous snakes. He is thought to have assumed that those animals acquired some detoxifying property, so that their blood would contain transformed components of the snake venom that could induce resistance to it instead of exerting a toxic effect. Mithridates reasoned that, by drinking the blood of these animals, he could acquire a similar resistance. Fearing assassination by poison, he took daily sub-lethal doses of venom to build tolerance. He is also said to have sought to create a 'universal antidote' to protect him from all poisons. For nearly 2000 years, poisons were thought to be the proximate cause of disease, and a complicated mixture of ingredients, called Mithridate, was used to cure poisoning during the
Renaissance The Renaissance ( , ) , from , with the same meanings. is a period in European history marking the transition from the Middle Ages to modernity and covering the 15th and 16th centuries, characterized by an effort to revive and surpass ide ...
. An updated version of this cure, Theriacum Andromachi, was used well into the 19th century. The term "immunes" is also found in the epic poem " Pharsalia" written around 60 BC by the poet Marcus Annaeus Lucanus to describe a North African tribe's resistance to snake venom. The first clinical description of immunity which arose from a specific disease-causing organism is probably ''A Treatise on Smallpox and Measles'' ("Kitab fi al-jadari wa-al-hasbah, translated 1848) written by the Islamic physician Al-Razi in the 9th century. In the treatise, Al Razi describes the clinical presentation of smallpox and measles and goes on to indicate that exposure to these specific agents confers lasting immunity (although he does not use this term). Until the 19th century, the miasma theory was also widely accepted. The theory viewed diseases such as cholera or the Black Plague as being caused by a miasma, a noxious form of "bad air". If someone was exposed to the miasma in a swamp, in evening air, or breathing air in a sickroom or hospital ward, they could catch a disease. Since the 19th century, communicable diseases came to be viewed as being caused by germs/microbes. The modern word "immunity" derives from the
Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...
immunis, meaning exemption from military service, tax payments or other public services. The first scientist who developed a full theory of immunity was Ilya Mechnikov who revealed phagocytosis in 1882. With Louis Pasteur's germ theory of disease, the fledgling science of immunology began to explain how bacteria caused disease, and how, following infection, the human body gained the ability to resist further infections. In 1888
Emile Roux Emil or Emile may refer to: Literature *''Emile, or On Education'' (1762), a treatise on education by Jean-Jacques Rousseau * ''Émile'' (novel) (1827), an autobiographical novel based on Émile de Girardin's early life *''Emil and the Detective ...
and
Alexandre Yersin Alexandre Emile Jean Yersin (22 September 1863 – 1 March 1943) was a Swiss-French physician and bacteriologist. He is remembered as the co-discoverer of the bacillus responsible for the bubonic plague or pest, which was later named in his ...
isolated
diphtheria toxin Diphtheria toxin is an exotoxin secreted by ''Corynebacterium diphtheriae'', the pathogenic bacterium that causes diphtheria. The toxin gene is encoded by a prophageA prophage is a virus that has inserted itself into the genome of the h ...
, and following the 1890 discovery by Behring and Kitasato of antitoxin based immunity to diphtheria and tetanus, the antitoxin became the first major success of modern therapeutic immunology. In
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
, the induction of active immunity emerged in an attempt to contain smallpox. Immunization has existed in various forms for at least a thousand years, without the terminology. The earliest use of immunization is unknown, but, about 1000 AD, the Chinese began practicing a form of immunization by drying and inhaling powders derived from the crusts of smallpox lesions. Around the 15th century in
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
, the
Ottoman Empire The Ottoman Empire, * ; is an archaic version. The definite article forms and were synonymous * and el, Оθωμανική Αυτοκρατορία, Othōmanikē Avtokratoria, label=none * info page on book at Martin Luther University ...
, and east Africa, the practice of inoculation (poking the skin with powdered material derived from smallpox crusts) was quite common. This practice was first introduced into the west in 1721 by Lady Mary Wortley Montagu. In 1798, Edward Jenner introduced the far safer method of deliberate infection with cowpox virus, ( smallpox vaccine), which caused a mild infection that also induced immunity to smallpox. By 1800, the procedure was referred to as
vaccination Vaccination is the administration of a vaccine to help the immune system develop immunity from a disease. Vaccines contain a microorganism or virus in a weakened, live or killed state, or proteins or toxins from the organism. In stimulat ...
. To avoid confusion, smallpox inoculation was increasingly referred to as variolation, and it became common practice to use this term without regard for chronology. The success and general acceptance of Jenner's procedure would later drive the general nature of vaccination developed by Pasteur and others towards the end of the 19th century. In 1891, Pasteur widened the definition of vaccine in honour of Jenner, and it then became essential to qualify the term by referring to polio vaccine, measles vaccine etc.


Passive immunity

Passive immunity is the immunity acquired by the transfer of ready-made antibodies from one individual to another. Passive immunity can occur naturally, such as when maternal antibodies are transferred to the foetus through the placenta, and can also be induced artificially, when high levels of human (or horse) antibodies specific for a
pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a g ...
or toxin are transferred to non- immune individuals. Passive immunization is used when there is a high risk of infection and insufficient time for the body to develop its own immune response, or to reduce the symptoms of ongoing or immunosuppressive diseases. Passive immunity provides immediate protection, but the body does not develop memory, therefore the patient is at risk of being infected by the same pathogen later..


Naturally acquired passive immunity

A fetus naturally acquires passive immunity from its mother during pregnancy. Maternal passive immunity is
antibody An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of t ...
-mediated immunity. The mother's antibodies (MatAb) are passed through the placenta to the fetus by an FcRn receptor on placental cells. This occurs around the third month of gestation. IgG is the only antibody isotype that can pass through the placenta. Passive immunity is also provided through the transfer of
IgA Iga may refer to: Arts and entertainment * Ambush at Iga Pass, a 1958 Japanese film * Iga no Kagemaru, Japanese manga series * Iga, a set of characters from the Japanese novel '' The Kouga Ninja Scrolls'' Biology * ''Iga'' (beetle), a g ...
antibodies found in breast milk that are transferred to the gut of a nursing infant, protecting against bacterial infections, until the newborn can synthesize its antibodies. Colostrum present in mothers milk is an example of passive immunity.


Artificially acquired passive immunity

Artificially acquired passive immunity is a short-term immunization induced by the transfer of antibodies, which can be administered in several forms; as human or animal blood plasma, as pooled human immunoglobulin for intravenous ( IVIG) or intramuscular (IG) use, and in the form of monoclonal antibodies (MAb). Passive transfer is used prophylactically in the case of immunodeficiency diseases, such as hypogammaglobulinemia. It is also used in the treatment of several types of acute infection, and to treat poisoning. Immunity derived from passive immunization lasts for only a short period of time, and there is also a potential risk for hypersensitivity reactions, and serum sickness, especially from gamma globulin of non-human origin. The artificial induction of passive immunity has been used for over a century to treat infectious disease, and before the advent of
antibiotics An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and preventio ...
, was often the only specific treatment for certain infections. Immunoglobulin therapy continued to be a first line therapy in the treatment of severe respiratory diseases until the 1930s, even after sulfonamide lot antibiotics were introduced.


Transfer of activated T-cells

Passive or " adoptive transfer" of cell-mediated immunity, is conferred by the transfer of "sensitized" or activated T-cells from one individual into another. It is rarely used in humans because it requires histocompatible (matched) donors, which are often difficult to find. In unmatched donors this type of transfer carries severe risks of graft versus host disease. It has, however, been used to treat certain diseases including some types of cancer and immunodeficiency. This type of transfer differs from a bone marrow transplant, in which (undifferentiated) hematopoietic stem cells are transferred.


Active immunity

When B cells and T cells are activated by a pathogen, memory B-cells and T- cells develop, and the primary immune response results. Throughout the lifetime of an animal, these memory cells will "remember" each specific pathogen encountered, and can mount a strong secondary response if the pathogen is detected again. The primary and secondary responses were first described in 1921 by English immunologist Alexander Glenny although the mechanism involved was not discovered until later. This type of immunity is both active and adaptive because the body's immune system prepares itself for future challenges. Active immunity often involves both the cell-mediated and humoral aspects of immunity as well as input from the innate immune system.


Naturally acquired

Naturally acquired active immunity occurs when a person is exposed to a live pathogen and develops a primary immune response, which leads to immunological memory. Many disorders of immune system function can affect the formation of active immunity such as immunodeficiency(both acquired and congenital forms) and immunosuppression.


Artificially acquired

Artificially acquired active immunity can be induced by a vaccine, a substance that contains antigen. A vaccine stimulates a primary response against the antigen without causing symptoms of the disease. The term vaccination was coined by Richard Dunning, a colleague of Edward Jenner, and adapted by Louis Pasteur for his pioneering work in vaccination. The method Pasteur used entailed treating the infectious agents for those diseases, so they lost the ability to cause serious disease. Pasteur adopted the name vaccine as a generic term in honor of Jenner's discovery, which Pasteur's work built upon. In 1807,
Bavaria Bavaria ( ; ), officially the Free State of Bavaria (german: Freistaat Bayern, link=no ), is a state in the south-east of Germany. With an area of , Bavaria is the largest German state by land area, comprising roughly a fifth of the total l ...
became the first group to require their military recruits to be vaccinated against smallpox, as the spread of smallpox was linked to combat. Subsequently, the practice of vaccination would increase with the spread of war. There are four types of traditional vaccines: * Inactivated vaccines are composed of micro-organisms that have been killed with chemicals and/or heat and are no longer infectious. Examples are vaccines against flu, cholera,
plague Plague or The Plague may refer to: Agriculture, fauna, and medicine *Plague (disease), a disease caused by ''Yersinia pestis'' * An epidemic of infectious disease (medical or agricultural) * A pandemic caused by such a disease * A swarm of pes ...
, and hepatitis A. Most vaccines of this type are likely to require booster shots. * Live, attenuated vaccines are composed of micro-organisms that have been cultivated under conditions which disable their ability to induce disease. These responses are more durable, however, they may require booster shots. Examples include yellow fever, measles, rubella, and mumps. *
Toxoid A toxoid is an inactivated toxin (usually an exotoxin) whose toxicity has been suppressed either by chemical (formalin) or heat treatment, while other properties, typically immunogenicity, are maintained. Toxins are secreted by bacteria, whereas ...
s are inactivated toxic compounds from micro-organisms in cases where these (rather than the micro-organism itself) cause illness, used prior to an encounter with the toxin of the micro-organism. Examples of toxoid-based vaccines include tetanus and diphtheria. *
Subunit Subunit may refer to: * Subunit HIV vaccine, a class of HIV vaccine *Protein subunit, a protein molecule that assembles with other protein molecules *Monomer, a molecule that may bind chemically to other molecules to form a polymer * Sub-subunit, ...
, recombinant, polysaccharide, and
conjugate vaccine A conjugate vaccine is a type of subunit vaccine which combines a weak antigen with a strong antigen as a carrier so that the immune system has a stronger response to the weak antigen. Vaccines are used to prevent diseases by invoking an immun ...
s are composed of small fragments or pieces from a pathogenic (disease-causing) organism. A characteristic example is the subunit vaccine against Hepatitis B virus. In addition, there are some newer types of vaccines in use: * Outer Membrane Vesicle (OMV) vaccines contain the outer membrane of a bacterium without any of its internal components or genetic material. Thus, ideally, they stimulate an immune response effective against the original bacteria without the risk of an infection. * Genetic vaccines deliver nucleic acid that codes for an antigen into host cells, which then produce that antigen, stimulating an immune response. This category of vaccine includes
DNA vaccine A DNA vaccine is a type of vaccine that transfects a specific antigen-coding DNA sequence into the cells of an organism as a mechanism to induce an immune response. DNA vaccines work by injecting genetically engineered plasmid containing the D ...
s, RNA vaccines, and viral vector vaccines, which differ in the chemical form of nucleic acid and how it is delivered into host cells. A variety of vaccine types are under development; see Experimental Vaccine Types. Most vaccines are given by hypodermic or
intramuscular Intramuscular injection, often abbreviated IM, is the injection of a substance into a muscle. In medicine, it is one of several methods for parenteral administration of medications. Intramuscular injection may be preferred because muscles ha ...
injection as they are not absorbed reliably through the gut. Live attenuated
polio Poliomyelitis, commonly shortened to polio, is an infectious disease caused by the poliovirus. Approximately 70% of cases are asymptomatic; mild symptoms which can occur include sore throat and fever; in a proportion of cases more severe sy ...
and some typhoid and cholera vaccines are given orally in order to produce immunity based in the bowel.


Hybrid immunity

Hybrid immunity is the combination of natural immunity and artificial immunity. Studies of hybrid-immune people found that their blood was better able to neutralize the Beta and other variants of SARS-CoV-2 than never-infected, vaccinated people. Moreover, on 29 October 2021, the Centers for Disease Control and Prevention (CDC) concluded that "Multiple studies in different settings have consistently shown that infection with SARS-CoV-2 and vaccination each result in a low risk of subsequent infection with antigenically similar variants for at least 6 months. Numerous immunologic studies and a growing number of epidemiologic studies have shown that vaccinating previously infected individuals significantly enhances their immune response and effectively reduces the risk of subsequent infection, including in the setting of increased circulation of more infectious variants. ... "


See also

*
Antiserum Antiserum is a blood serum containing monoclonal or polyclonal antibodies that is used to spread passive immunity to many diseases via blood donation (plasmapheresis). For example, convalescent serum, passive antibody transfusion from a previous ...
* Antivenin *
Cell-mediated immunity Cell-mediated immunity or cellular immunity is an immune response that does not involve antibodies. Rather, cell-mediated immunity is the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines ...
*
Herd immunity Herd immunity (also called herd effect, community immunity, population immunity, or mass immunity) is a form of indirect protection that applies only to contagious diseases. It occurs when a sufficient percentage of a population has become im ...
* Heterosubtypic immunity * Hoskins effect * Humoral immunity * Immunology * Inoculation * Premunity *
Vaccine-naive Vaccine-naive is a lack of immunity, or immunologic memory, to a disease because the person has not been vaccinated. There are a variety of reasons why a person may not have received a vaccination, including contraindications due to preexisting m ...
*
Virgin soil epidemic Virgin soil epidemic is a term coined by Alfred Crosby, who defined it as epidemics "in which the populations at risk have had no previous contact with the diseases that strike them and are therefore immunologically almost defenseless." His con ...


References


External links


The Center for Modeling Immunity to Enteric Pathogens (MIEP)
{{Authority control Immunology