In biology, immunity is the capability of

multicellular organisms A multicellular organism is an organism that consists of more than one cell, in contrast to unicellular organism. All species of animals, land plants and most fungi are multicellular, as are many algae, whereas a few organisms are partially uni ...

to resist harmful microorganisms. Immunity involves both specific and nonspecific components. The nonspecific components act as barriers or eliminators of a wide range of pathogens irrespective of their antigenic make-up. Other components of the immune system 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. Fc receptor schematic big

The immune system has

innate {{Short pages monitor 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 In law and insurance, a proximate cause is an event sufficiently related to an injury that the courts deem the event to be the cause of that injury. There are two types of causation in the law: cause-in-fact, and proximate (or legal) cause. Ca ...

of disease, and a complicated mixture of ingredients, called

Mithridate Mithridate, also known as mithridatium, mithridatum, or mithridaticum, is a semi-mythical remedy with as many as 65 ingredients, used as an antidote for poisoning, and said to have been created by Mithridates VI Eupator of Pontus in the 1st cent ...

, was used to cure poisoning during the

Renaissance The Renaissance ( , ) , from , with the same meanings. is a period in European history The history of Europe is traditionally divided into four time periods: prehistoric Europe (prior to about 800 BC), classical antiquity (800 BC to AD ...

. 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 ''De Bello Civili'' (; ''On the Civil War''), more commonly referred to as the ''Pharsalia'', is a Roman epic poem written by the poet Lucan, detailing the civil war between Julius Caesar and the forces of the Roman Senate led by Pompey the Gr ...

" written around 60 BC by the poet

Marcus Annaeus Lucanus Marcus Annaeus Lucanus (3 November 39 AD – 30 April 65 AD), better known in English as Lucan (), was a Roman poet, born in Corduba (modern-day Córdoba), in Hispania Baetica. He is regarded as one of the outstanding figures of the Imperial ...

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 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 the power of the ...

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 Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs phagocytosis is ...

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. Albert Edelfelt - Louis Pasteur - 1885

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 An antitoxin is an antibody with the ability to neutralize a specific toxin. Antitoxins are produced by certain animals, plants, and bacteria in response to toxin exposure. Although they are most effective in neutralizing toxins, they can also ...

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 subcontinent of Eurasia and it is located entirel ...

, the induction of active immunity emerged in an attempt to contain

smallpox Smallpox was an infectious disease caused by variola virus (often called smallpox virus) which belongs to the genus Orthopoxvirus. The last naturally occurring case was diagnosed in October 1977, and the World Health Organization (WHO) c ...

. 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 seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...

, 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 Edward Jenner, (17 May 1749 – 26 January 1823) was a British physician and scientist who pioneered the concept of vaccines, and created the smallpox vaccine, the world's first vaccine. The terms ''vaccine'' and ''vaccination'' are derived f ...

introduced the far safer method of deliberate infection with

cowpox Cowpox is an infectious disease caused by the ''cowpox virus'' (CPXV). It presents with large blisters in the skin, a fever and swollen glands, historically typically following contact with an infected cow, though in the last several decades more ...

virus, (

smallpox vaccine The smallpox vaccine is the first vaccine to be developed against a contagious disease. In 1796, British physician Edward Jenner demonstrated that an infection with the relatively mild cowpox virus conferred immunity against the deadly smallpox ...

), 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 Variolation was the method of inoculation first used to immunize individuals against smallpox (''Variola'') with material taken from a patient or a recently variolated individual, in the hope that a mild, but protective, infection would result. Var ...

, 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 Polio vaccines are vaccines used to prevent poliomyelitis (polio). Two types are used: an inactivated poliovirus given by injection (IPV) and a weakened poliovirus given by mouth (OPV). The World Health Organization (WHO) recommends all chi ...

measles vaccine Measles vaccine protects against becoming infected with measles. Nearly all of those who do not develop immunity after a single dose develop it after a second dose. When rate of vaccination within a population is greater than 92%, outbreaks o ...

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 Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, cultu ...

(or

horse The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million yea ...

) 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 Immunosuppression is a reduction of the activation or efficacy of the immune system. Some portions of the immune system itself have immunosuppressive effects on other parts of the immune system, and immunosuppression may occur as an adverse reacti ...

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. Antitoxin diphtheria

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 Immunoglobulin therapy is the use of a mixture of antibodies (normal human immunoglobulin or NHIG) to treat several health conditions. These conditions include primary immunodeficiency, immune thrombocytopenic purpura, chronic inflammatory ...

) or intramuscular (IG) use, and in the form of monoclonal antibodies (MAb). Passive transfer is used

prophylactic Preventive healthcare, or prophylaxis, consists of measures taken for the purposes of disease prevention.Hugh R. Leavell and E. Gurney Clark as "the science and art of preventing disease, prolonging life, and promoting physical and mental hea ...

ally in the case of immunodeficiency diseases, such as

hypogammaglobulinemia Hypogammaglobulinemia is a problem with the immune system in which not enough gamma globulins are produced in the blood (thus '' hypo-'' + ''gamma'' + ''globulin'' + '' -emia''). This results in a lower antibody count, which impairs the immune sys ...

. 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 Hypersensitivity (also called hypersensitivity reaction or intolerance) refers to undesirable reactions produced by the normal immune system, including allergies and autoimmunity. They are usually referred to as an over-reaction of the immune ...

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 prevention o ...

, was often the only specific treatment for certain infections. Immunoglobulin therapy continued to be a first line therapy in the treatment of severe

respiratory disease Respiratory diseases, or lung diseases, are pathological conditions affecting the organs and tissues that make gas exchange difficult in air-breathing animals. They include conditions of the respiratory tract including the trachea, bronchi, bro ...

s 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 Graft-versus-host disease (GvHD) is a syndrome, characterized by inflammation in different organs. GvHD is commonly associated with bone marrow transplants and stem cell transplants. White blood cells of the donor's immune system which remain wit ...

. It has, however, been used to treat certain diseases including some types of

cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...

and immunodeficiency. This type of transfer differs from a

bone marrow transplant Hematopoietic stem-cell transplantation (HSCT) is the transplantation of multipotent hematopoietic stem cells, usually derived from bone marrow, peripheral blood, or umbilical cord blood in order to replicate inside of a patient and to produce ...

, in which (undifferentiated) hematopoietic stem cells are transferred.

Active immunity

When

B cells B cells, also known as B lymphocytes, are a type of white blood cell of the lymphocyte subtype. They function in the humoral immunity component of the adaptive immune system. B cells produce antibody molecules which may be either secreted o ...

and

T cells A T cell is a type of lymphocyte. T cells are one of the important white blood cells of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell re ...

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 Immunosuppression is a reduction of the activation or efficacy of the immune system. Some portions of the immune system itself have immunosuppressive effects on other parts of the immune system, and immunosuppression may occur as an adverse reacti ...

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

, 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. Poster for vaccination against smallpox

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 lan ...

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, 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 Yellow fever is a viral disease of typically short duration. In most cases, symptoms include fever, chills, loss of appetite, nausea, muscle pains – particularly in the back – and headaches. Symptoms typically improve within five days. ...

, measles, rubella, and mumps. * Toxoids 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, recombinant, polysaccharide, and conjugate vaccines are composed of small fragments or pieces from a pathogenic (disease-causing) organism. A characteristic example is the subunit vaccine against

Hepatitis B virus ''Hepatitis B virus'' (HBV) is a partially double-stranded DNA virus, a species of the genus '' Orthohepadnavirus'' and a member of the '' Hepadnaviridae'' family of viruses. This virus causes the disease hepatitis B. Disease Despite there b ...

. 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 vaccines,

RNA vaccine An mRNA vaccine is a type of vaccine that uses a copy of a molecule called messenger RNA (mRNA) to produce an immune response. The vaccine delivers molecules of antigen-encoding mRNA into immune cells, which use the designed mRNA as a blueprin ...

s, 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 A hypodermic needle (from Greek ὑπο- (''hypo-'' = under), and δέρμα (''derma'' = skin)), one of a category of medical tools which enter the skin, called sharps, is a very thin, hollow tube with one sharp tip. It is commonly used w ...

or intramuscular injection as they are not absorbed reliably through the gut. Live attenuated polio and some typhoid and cholera vaccines are given orally in order to produce immunity based in the

bowel The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and ...

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. ... "

References

External links

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