immunity (medical) immunity (medical) in biology, immunity is the state of being insusceptible or resistant to a noxious agent or process, especially a pathogen or infectious disease. immunity may occur naturally or be produced by prior exposure or immunization. innate and adaptive scheme of a fc receptor the immune system has innate and adaptive components. innate immunity is present in all metazoans, 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 a representation of the cholera epidemic of the 19th century 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 (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: "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 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. 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 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. louis pasteur in his laboratory, 1885, by albert edelfelt in 1888 emile roux and alexandre yersin isolated diphtheria toxin, 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, 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, the ottoman empire, 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. 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 main article: 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 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-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 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. one of the first bottles of diphtheria antitoxin produced (dated 1895) artificially acquired passive immunity