biology Biology is the scientific study of life and living organisms. It is a broad natural science that encompasses a wide range of fields and unifying principles that explain the structure, function, growth, History of life, origin, evolution, and ...

pathogen In biology, a pathogen (, "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 Germ theory of d ...

infectious disease An infection is the invasion of tissue (biology), tissues by pathogens, their multiplication, and the reaction of host (biology), host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmis ...

immunization Immunization, or immunisation, is the process by which an individual's immune system becomes fortified against an infectious agent (known as the antigen, immunogen). When this system is exposed to molecules that are foreign to the body, called ' ...

immune system The immune system is a network of biological systems that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to bacteria, as well as Tumor immunology, cancer cells, Parasitic worm, parasitic ...

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, was used to cure poisoning during the

Renaissance The Renaissance ( , ) is a Periodization, period of history and a European cultural movement covering the 15th and 16th centuries. It marked the transition from the Middle Ages to modernity and was characterized by an effort to revive and sur ...

. 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'' (, neuter plural), is a Latin literature, Roman Epic poetry, epic poem written by the poet Lucan, detailing the Caesar's civil war, civil war between Ju ...

" written around 60 BC by the poet Marcus Annaeus Lucanus to describe a North African tribe's resistance to

snake venom Snake venom is a highly toxic saliva containing zootoxins that facilitates in the immobilization and digestion of prey. This also provides defense against threats. Snake venom is usually injected by unique fangs during a Snakebite, bite, though ...

. 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 Islam is an Abrahamic religions, Abrahamic monotheistic religion based on the Quran, and the teachings of Muhammad. Adherents of Islam are called Muslims, who are estimated to number Islam by country, 2 billion worldwide and are the world ...

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 The miasma theory (also called the miasmic theory) is an abandoned medical theory that held that diseases—such as cholera, chlamydia, or plague—were caused by a ''miasma'' (, Ancient Greek for 'pollution'), a noxious form of "bad air", a ...

was also widely accepted. The theory viewed diseases such as

cholera Cholera () is an infection of the small intestine by some Strain (biology), strains of the Bacteria, bacterium ''Vibrio cholerae''. Symptoms may range from none, to mild, to severe. The classic symptom is large amounts of watery diarrhea last ...

or the

Black Plague The Black Death was a bubonic plague pandemic that occurred in Europe from 1346 to 1353. It was one of the list of epidemics, most fatal pandemics in human history; as many as people perished, perhaps 50% of Europe's 14th century population. ...

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 spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

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 (biology), 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 ph ...

in 1882. With

Louis Pasteur Louis Pasteur (, ; 27 December 1822 – 28 September 1895) was a French chemist, pharmacist, and microbiologist renowned for his discoveries of the principles of vaccination, Fermentation, microbial fermentation, and pasteurization, the la ...

's

germ theory of disease The germ theory of disease is the currently accepted scientific theory for many diseases. It states that microorganisms known as pathogens or "germs" can cause disease. These small organisms, which are too small to be seen without magnification, ...

, the fledgling science of

immunology Immunology is a branch of biology and medicine that covers the study of Immune system, immune systems in all Organism, organisms. Immunology charts, measures, and contextualizes the Physiology, physiological functioning of the immune system in ...

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 Diphtheria toxin is an exotoxin secreted mainly by '' Corynebacterium diphtheriae'' but also by ''Corynebacterium ulcerans'' and '' Corynebacterium pseudotuberculosis'', the pathogenic bacterium that causes diphtheria. The toxin gene is enco ...

, and following the 1890 discovery by Behring and Kitasato of antitoxin based immunity to

diphtheria Diphtheria is an infection caused by the bacteria, bacterium ''Corynebacterium diphtheriae''. Most infections are asymptomatic or have a mild Course (medicine), clinical course, but in some outbreaks, the mortality rate approaches 10%. Signs a ...

and

tetanus Tetanus (), also known as lockjaw, is a bacterial infection caused by ''Clostridium tetani'' and characterized by muscle spasms. In the most common type, the spasms begin in the jaw and then progress to the rest of the body. Each spasm usually l ...

, the

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

became the first major success of modern therapeutic immunology. In

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

, 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 (W ...

. 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, 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 by population (United Nations), most populous country since ...

, the

Ottoman Empire The Ottoman Empire (), also called the Turkish Empire, was an empire, imperial realm that controlled much of Southeast Europe, West Asia, and North Africa from the 14th to early 20th centuries; it also controlled parts of southeastern Centr ...

, and

east Africa East Africa, also known as Eastern Africa or the East of Africa, is a region at the eastern edge of the Africa, African continent, distinguished by its unique geographical, historical, and cultural landscape. Defined in varying scopes, the regi ...

, the practice of

inoculation Inoculation is the act of implanting a pathogen or other microbe or virus into a person or other organism. It is a method of artificially inducing immunity against various infectious diseases. The term "inoculation" is also used more generally ...

(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 an English 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 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 often ...

virus, (

smallpox vaccine The smallpox vaccine is used to prevent smallpox infection caused by the variola virus. It is the first vaccine to have been developed against a contagious disease. In 1796, British physician Edward Jenner demonstrated that an infection with th ...

), 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 stimulating ...

. 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. On ...

, 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 A vaccine is a biological Dosage form, preparation that provides active acquired immunity to a particular infectious disease, infectious or cancer, malignant disease. The safety and effectiveness of vaccines has been widely studied and verifi ...

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 vaccine, inactivated poliovirus given by injection (IPV) and a attenuated vaccine, weakened poliovirus given by mouth (OPV). The World Healt ...

, measles vaccine etc.

Passive immunity

Passive immunity is the immunity acquired by the transfer of ready-made

antibodies An antibody (Ab) or immunoglobulin (Ig) is a large, Y-shaped protein belonging to the immunoglobulin superfamily which is used by the immune system to identify and neutralize antigens such as bacteria and viruses, including those that caus ...

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'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

(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 mi ...

) antibodies specific for a

pathogen In biology, a pathogen (, "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 Germ theory of d ...

or

toxin A toxin is a naturally occurring poison produced by metabolic activities of living cells or organisms. They occur especially as proteins, often conjugated. The term was first used by organic chemist Ludwig Brieger (1849–1919), derived ...

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 A fetus or foetus (; : fetuses, foetuses, rarely feti or foeti) is the unborn offspring of a viviparous animal that develops from an embryo. Following the embryonic development, embryonic stage, the fetal stage of development takes place. Pren ...

naturally acquires passive immunity from its mother during pregnancy. Maternal passive immunity is

antibody An antibody (Ab) or immunoglobulin (Ig) is a large, Y-shaped protein belonging to the immunoglobulin superfamily which is used by the immune system to identify and neutralize antigens such as pathogenic bacteria, bacteria and viruses, includin ...

-mediated immunity. The mother's antibodies (MatAb) are passed through the

placenta The placenta (: placentas or placentae) is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas, and waste exchange between ...

to the fetus by an FcRn receptor on placental cells. This occurs around the third month of

gestation Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals (the embryo develops within the parent). It is typical for mammals, but also occurs for some non-mammals. Mammals during pregn ...

. 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 Breast milk (sometimes spelled as breastmilk) or mother's milk is milk produced by the mammary glands in the breasts of women. Breast milk is the primary source of nutrition for newborn infants, comprising fats, proteins, carbohydrates, and a var ...

that are transferred to the gut of a nursing infant, protecting against bacterial infections, until the newborn can synthesize its antibodies.

Colostrum Colostrum (, of unknown origin) is the first form of milk produced by the mammary glands of humans and other mammals immediately following delivery of the newborn. Animal colostrum may be called beestings, the traditional word from Old English ...

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) or intramuscular (IG) use, and in the form of

monoclonal antibodies A monoclonal antibody (mAb, more rarely called moAb) is an antibody produced from a Lineage (evolution), cell lineage made by cloning a unique white blood cell. All subsequent antibodies derived this way trace back to a unique parent cell. Mon ...

(MAb). Passive transfer is used prophylactically in the case of

immunodeficiency Immunodeficiency, also known as immunocompromise, is a state in which the immune system's ability to fight infectious diseases and cancer is compromised or entirely absent. Most cases are acquired ("secondary") due to extrinsic factors that aff ...

diseases, such as hypogammaglobulinemia. It is also used in the treatment of several types of acute infection, and to treat

poison A poison is any chemical substance that is harmful or lethal to living organisms. The term is used in a wide range of scientific fields and industries, where it is often specifically defined. It may also be applied colloquially or figurati ...

ing. 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) is an abnormal physiological condition in which there is an undesirable and adverse immune response to an antigen. It is an abnormality in the immune system that causes Imm ...

reactions, and

serum sickness Serum sickness in humans is a adverse drug reaction, reaction to proteins in antiserum derived from a non-human animal source, occurring 5–10 days after exposure. Symptoms often include a rash, Arthralgia, joint pain, fever, and lymphadenopathy. ...

, 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 pathogenic bacteria, bacterial infections, and antibiotic medications are widely used in the therapy ...

, 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, ...

s until the 1930s, even after

sulfonamide In organic chemistry, the sulfonamide functional group (also spelled sulphonamide) is an organosulfur group with the Chemical structure, structure . It consists of a sulfonyl group () connected to an amine group (). Relatively speaking this gro ...

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 Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the potential to Invasion (cancer), invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not spread. Po ...

and

immunodeficiency Immunodeficiency, also known as immunocompromise, is a state in which the immune system's ability to fight infectious diseases and cancer is compromised or entirely absent. Most cases are acquired ("secondary") due to extrinsic factors that aff ...

. 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 a patient and produce a ...

, in which (undifferentiated)

hematopoietic stem cell Hematopoietic stem cells (HSCs) are the stem cells that give rise to other blood cells. This process is called haematopoiesis. In vertebrates, the first definitive HSCs arise from the ventral endothelial wall of the embryonic aorta within the ...

s are transferred.

Active immunity

When

B cells B cells, also known as B lymphocytes, are a type 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 or inserted into the plasm ...

and

T cells T cells (also known as T lymphocytes) are an important part 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 receptor (TCR) on their ce ...

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 The innate immune system or nonspecific immune system is one of the two main immunity strategies in vertebrates (the other being the adaptive immune system). The innate immune system is an alternate defense strategy and is the dominant immune s ...

.

Naturally acquired

Naturally acquired active immunity occurs as the result of surviving an infection. When a person is exposed to a live pathogen and develops a primary

immune response An immune response is a physiological reaction which occurs within an organism in the context of inflammation for the purpose of defending against exogenous factors. These include a wide variety of different toxins, viruses, intra- and extracellula ...

, this leads to immunological memory. Many disorders of immune system function can affect the formation of active immunity, such as

immunodeficiency Immunodeficiency, also known as immunocompromise, is a state in which the immune system's ability to fight infectious diseases and cancer is compromised or entirely absent. Most cases are acquired ("secondary") due to extrinsic factors that aff ...

(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 react ...

.

Artificially acquired

Artificially acquired active immunity can be induced by a

vaccine A vaccine is a biological Dosage form, preparation that provides active acquired immunity to a particular infectious disease, infectious or cancer, malignant disease. The safety and effectiveness of vaccines has been widely studied and verifi ...

, 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 Edward Jenner (17 May 1749 – 26 January 1823) was an English 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 ...

, and adapted by

Louis Pasteur Louis Pasteur (, ; 27 December 1822 – 28 September 1895) was a French chemist, pharmacist, and microbiologist renowned for his discoveries of the principles of vaccination, Fermentation, microbial fermentation, and pasteurization, the la ...

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, is a States of Germany, state in the southeast of Germany. With an area of , it is the list of German states by area, largest German state by land area, comprising approximately 1/5 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

vaccine A vaccine is a biological Dosage form, preparation that provides active acquired immunity to a particular infectious disease, infectious or cancer, malignant disease. The safety and effectiveness of vaccines has been widely studied and verifi ...

s: * 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 Cholera () is an infection of the small intestine by some Strain (biology), strains of the Bacteria, bacterium ''Vibrio cholerae''. Symptoms may range from none, to mild, to severe. The classic symptom is large amounts of watery diarrhea last ...

, 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,

measles Measles (probably from Middle Dutch or Middle High German ''masel(e)'', meaning "blemish, blood blister") is a highly contagious, Vaccine-preventable diseases, vaccine-preventable infectious disease caused by Measles morbillivirus, measles v ...

,

rubella Rubella, also known as German measles or three-day measles, is an infection caused by the rubella virus. This disease is often mild, with half of people not realizing that they are infected. A rash may start around two weeks after exposure and ...

, and

mumps MUMPS ("Massachusetts General Hospital Utility Multi-Programming System"), or M, is an imperative, high-level programming language with an integrated transaction processing key–value database. It was originally developed at Massachusetts Gen ...

. *

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, wherea ...

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 Tetanus (), also known as lockjaw, is a bacterial infection caused by ''Clostridium tetani'' and characterized by muscle spasms. In the most common type, the spasms begin in the jaw and then progress to the rest of the body. Each spasm usually l ...

and

diphtheria Diphtheria is an infection caused by the bacteria, bacterium ''Corynebacterium diphtheriae''. Most infections are asymptomatic or have a mild Course (medicine), clinical course, but in some outbreaks, the mortality rate approaches 10%. Signs a ...

. * Subunit, recombinant,

polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long-chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with wat ...

, 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. Classification Hepatitis 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 Nucleic acids are large biomolecules that are crucial in all cells and viruses. They are composed of nucleotides, which are the monomer components: a pentose, 5-carbon sugar, a phosphate group and a nitrogenous base. The two main classes of nuclei ...

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 vaccines, and

viral vector vaccine A viral vector vaccine is a vaccine that uses a viral vector to deliver genetic material (DNA) that can be transcribed by the recipient's host cells as mRNA coding for a desired protein, or antigen, to elicit an immune response. , six viral vector ...

s, 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 hav ...

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 75% of cases are asymptomatic; mild symptoms which can occur include sore throat and fever; in a proportion of cases more severe ...

and some

typhoid Typhoid fever, also known simply as typhoid, is a disease caused by ''Salmonella enterica'' serotype Typhi bacteria, also called ''Salmonella'' Typhi. Symptoms vary from mild to severe, and usually begin six to 30 days after exposure. Often ther ...

and

cholera Cholera () is an infection of the small intestine by some Strain (biology), strains of the Bacteria, bacterium ''Vibrio cholerae''. Symptoms may range from none, to mild, to severe. The classic symptom is large amounts of watery diarrhea last ...

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 tract is the largest of the body's systems, after the cardiovascular system. T ...

.

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 Severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) is a strain of coronavirus that causes COVID-19, the respiratory illness responsible for the COVID-19 pandemic. The virus previously had the Novel coronavirus, provisional nam ...

than never-infected, vaccinated people. Moreover, on 29 October 2021, the

Centers for Disease Control and Prevention The Centers for Disease Control and Prevention (CDC) is the National public health institutes, national public health agency of the United States. It is a Federal agencies of the United States, United States federal agency under the United S ...

(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. ..."

Genetics

Immunity is determined genetically.

Genome A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...

s in humans and

animal Animals are multicellular, eukaryotic organisms in the Biology, biological Kingdom (biology), kingdom Animalia (). With few exceptions, animals heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, ...

s encode the

antibodies An antibody (Ab) or immunoglobulin (Ig) is a large, Y-shaped protein belonging to the immunoglobulin superfamily which is used by the immune system to identify and neutralize antigens such as bacteria and viruses, including those that caus ...

and numerous other immune response genes. While many of these genes are generally required for active and passive immune responses (see sections above), there are also many

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

s that appear to be required for very specific immune responses. For instance,

Tumor Necrosis Factor Tumor necrosis factor (TNF), formerly known as TNF-α, is a chemical messenger produced by the immune system that induces inflammation. TNF is produced primarily by activated macrophages, and induces inflammation by binding to its receptors o ...

(TNF) is required for defense of

tuberculosis Tuberculosis (TB), also known colloquially as the "white death", or historically as consumption, is a contagious disease usually caused by ''Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can al ...

in humans. Individuals with genetic defects in TNF may get recurrent and life-threatening infections with tuberculosis bacteria (''

Mycobacterium tuberculosis ''Mycobacterium tuberculosis'' (M. tb), also known as Koch's bacillus, is a species of pathogenic bacteria in the family Mycobacteriaceae and the causative agent of tuberculosis. First discovered in 1882 by Robert Koch, ''M. tuberculosis'' ha ...

'') but are otherwise healthy. They also seem to respond to other infections more or less normally. The condition is therefore called ''Mendelian susceptibility to mycobacterial disease'' (MSMD) and variants of it can be caused by other genes related to

interferon Interferons (IFNs, ) are a group of signaling proteins made and released by host cells in response to the presence of several viruses. In a typical scenario, a virus-infected cell will release interferons causing nearby cells to heighten ...

production or signaling (e.g. by mutations in the genes '' IFNG'', '' IL12B'', '' IL12RB1'', '' IL12RB2'', '' IL23R'', '' ISG15'', '' MCTS1'', '' RORC'', '' TBX21'', ''

TYK2 Non-receptor tyrosine-protein kinase TYK2 is an enzyme that in humans is encoded by the ''TYK2'' gene. TYK2 was the first member of the Janus kinase, JAK family that was described (the other members are Janus kinase 1, JAK1, Janus kinase 2, JAK2, ...

'', '' CYBB'', '' JAK1'', '' IFNGR1'', '' IFNGR2'', '' STAT1'', '' USP18,'' '' IRF1'', '' IRF8'', ''NEMO'', '' SPPL2A'').

References

External links

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

Innate and adaptive

Passive immunity

Naturally acquired passive immunity

Artificially acquired passive immunity

Transfer of activated T-cells

Active immunity

Naturally acquired

Artificially acquired

Hybrid immunity

Genetics

See also

References

External links