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Immunology

KEY TERMS

Resources

Immunology is the study of how the body responds to foreign substances and fights off infection and other disease. Immunologists study the molecules, cells, and organs of the human body that participate in this response.

The beginnings of our understanding of immunity date to 1798, when the English physician Edward Jenner (17491823) published a report that people could be protected from deadly smallpox by sticking them with a needle dipped in the material from a cow-pox boil. The French biologist and chemist Louis Pasteur (18221895) theorized that such immunization protects people against disease by exposing them to a version of a microbe that is harmless but is enough like the disease-causing organism, or pathogen, that the immune system learns to fight it. Modern vaccines against diseases such as measles, polio, and chicken-pox are based on this principle.

In the late nineteenth century, a scientific debate was waged between the German physician Paul Ehrlich (18541915) and the Russian zoologist Elie Metchnikoff (18451916). Ehrlich and his followers believed that proteins in the blood, called antibodies, eliminated pathogens by sticking to them; this phenomenon became known as humoral immunity. Metchnikoff and his students, on the other hand, noted that certain white blood cells could engulf and digest foreign materials: this cellular immunity, they claimed, was the real way the body fought infection.

Modern immunologists have shown that both the humoral and cellular responses play a role in fighting disease. They have also identified many of the actors and processes that form the immune response.

The immune response recognizes and responds to pathogens via a network of cells that communicate with each other about what they have seen and whether it belongs. These cells patrol throughout the body for infection, carried by both the blood stream and the lymph ducts, a series of vessels carrying a clear fluid rich in immune cells.

The antigen presenting cells are the first line of the bodys defense, the scouts of the immune army. They engulf foreign material or microorganisms and digest them, displaying bits and pieces of the invaders, called antigensfor other immune cells to identify. These other immune cells, called T lymphocytes, can then begin the immune response that attacks the pathogen.

The bodys other cells can also present antigens, although in a slightly different way. Cells always display antigens from their everyday proteins on their surface. When a cell is infected with a virus, or when it becomes cancerous, it will often make unusual proteins whose antigens can then be identified by any of a variety of cytotoxic T lymphocytes. These killer cells then destroy the infected or cancerous cell to protect the rest of the body. Other T lymphocytes generate chemical or other signals that encourage multiplication of other infection-fighting cells. Various types of T lymphocytes are a central part of the cellular immune response; they are also involved in the humoral response, encouraging B lymphocytes to turn into antibody-producing plasma cells.

The body cannot know in advance what a pathogen will look like and how to fight it, so it creates millions and millions of different lymphocytes that recognize random antigens. When, by chance, a B or T lymphocyte recognizes an antigen being displayed by an antigen-presenting cell, the lymphocyte divides and produces many offspring that can also identify and attack this antigen. The way the immune system expands cells that by chance can attack an invading microbe is called clonal selection.

Some researchers believe that while some B and T lymphocytes recognize a pathogen and begin to mature and fight an infection, others stick around in the bloodstream for months or even years in a primed condition. Such memory cells may be the basis for the immunity noted by the ancient Chinese and by Thucydides. Other immunologists believe instead that trace amounts of a pathogen persist in the body, and their continued presence keeps the immune response strong over time.

Substances foreign to the body, such as disease-causing bacteria, viruses, and other infectious agents (known as antigens), are recognized by the bodys immune system as invaders. The bodys natural defenses against these infectious agents are antibodiesproteins that seek out the antigens and help destroy them. Antibodies have two very useful characteristics. First, they are extremely specific; that is, each antibody binds to and attacks one particular antigen. Second, some antibodies, once activated by the occurrence of a disease, continue to confer resistance against that disease; classic examples are the antibodies to the childhood diseases chickenpox and measles.

The second characteristic of antibodies makes it possible to develop vaccines. A vaccine is a preparation of killed or weakened bacteria or viruses that, when introduced into the body, stimulates the production of antibodies against the antigens it contains.

It is the first trait of antibodies, their specificity, that makes monoclonal antibody technology so valuable. Not only can antibodies be used therapeutically, to protect against disease; they can also help to diagnose a wide variety of illnesses, and can detect the presence of drugs, viral and bacterial products, and other unusual or abnormal substances in the blood.

Given such a diversity of uses for these disease-fighting substances, their production in pure quantities has long been the focus of scientific investigation. The conventional method was to inject a laboratory animal with an antigen and then, after antibodies had been formed, collect those antibodies from the blood serum (antibody-containing blood serum is called antiserum). There are two problems with this method: It yields antiserum that contains undesired substances, and it provides a very small amount of usable antibody.

Monoclonal antibody technology allows the production of large amounts of pure antibodies in the following way. Cells that produce antibodies naturally are obtained along with a class of cells that can grow continually in cell culture. The hybrid resulting from combining cells with the characteristic of immortality and those with the ability to produce the desired substance, creates, in effect, a factory to produce antibodies that work around the clock.

A myeloma is a tumor of the bone marrow that can be adapted to grow permanently in cell culture. Fusing myeloma cells with antibody-producing mammalian spleen cells, results in hybrid cells, or hybridomas, producing large amounts of monoclonal antibodies. This product of cell fusion combined the desired qualities of the two different types of cells, the ability to grow continually, and the ability to produce large amounts of pure antibody. Because selected hybrid cells produce only one specific antibody, they are more pure than the polyclonal antibodies produced by conventional techniques. They are potentially more effective than conventional drugs in fighting disease, because drugs attack not only the foreign substance but also the bodys own cells as well, sometimes producing undesirable side effects such as nausea and allergic reactions. Monoclonal antibodies attack the target molecule and only the target molecule, with no or greatly diminished side effects.

While researchers have made great gains in understanding immunity, many big questions remain. Future research will need to identify how the immune response is coordinated. Other researchers are studying the immune systems of non-mammals, trying to

KEY TERMS

Autoimmunity An aberrant immune response that attacks the bodys own tissues.

Cellular immunity The arm of the immune system that uses cells and their activities to kill pathogens, infected cells, and cancer cells.

Clonal selection The process whereby one or a few immune cells that by chance recognize an antigen multiply when the antigen is present in the body.

Humoral immunity The arm of the immune system that uses antibodies and other chemicals to clear pathogens from the body and to kill infected or cancerous cells.

Immunodeficiency A condition where the immune response is weak or incomplete, allowing pathogens to cause disease more easily. AIDS is a kind of immunodeficiency.

learn how our immune response evolved. Insects, for instance, lack antibodies, and are protected only by cellular immunity and chemical defenses not known to be present in higher organisms.

Immunologists do not yet know the details behind allergy, where antigens like those from pollen, poison ivy, or certain kinds of food make the body start an uncomfortable, unnecessary, and occasionally life-threatening immune response. Likewise, no one knows exactly why the immune system can suddenly attack the bodys tissuesas in autoimmune diseases like rheumatoid arthritis, juvenile diabetes, systemic lupus erythema-tosus, or multiple sclerosis.

The hunt continues for new vaccines, especially against parasitic organisms like the malaria microbe that trick the immune system by changing their antigens. Some researchers are seeking ways to start an immune response that prevents or kills cancers. A big goal of immunologists is the search for a vaccine for HIV (human immunodeficiency virus), the virus that causes AIDS (acquired immunodeficiency syndrome). HIV knocks out the immune systemcausing immunodeficiencyby infecting crucial T lymphocytes. Some immunologists have suggested that the chiefly humoral response raised by conventional vaccines may be unable to stop HIV from getting to lymphocytes, and that a new kind of vaccine that encourages a cellular response may be more effective.

Researchers have shown that transplant rejection is just another kind of immune response, with the immune system attacking antigens in the transplanted organ that are different from its own. Drugs that suppress the immune system are now used to prevent rejection, but they also make the patient vulnerable to infection. Immunologists are using their increased understanding of the immune system to develop more subtle ways of deceiving the immune system into accepting transplants.

Resources

BOOKS

Abbas, Abdul K., and Andrew H. Lichtman. Basic Immunology, Updated Edition 2006-2007: with STUDENT CONSULT Access. New York: Saunders, 2006.

Roitt, Ivan M., Seamus J. Martin, Peter J. Delves, and Dennis Burton. Roitts Essential Immunology. Boston: Blackwell Publishing, 2006.

Rose, N.R. Manual of Clinical Laboratory Immunology. 4th ed. Washington: American Society for Microbiology, 2002.

Kenneth B. Chiacchia

views updated

Immunology

Immunology is the study of how the body responds to foreign substances and fights off infection and other disease. Immunologists study the molecules, cells, and organs of the human body that participate in this response.

The beginnings of our understanding of immunity date to 1798, when the English physician Edward Jenner (17491823) published a report that people could be protected from deadly smallpox by sticking them with a needle dipped in the material from a cowpox boil. The French biologist and chemist Louis Pasteur (18221895) theorized that such immunization protects people against disease by exposing them to a version of a microbe that is harmless but is enough like the disease-causing organism, or pathogen, that the immune system learns to fight it. Modern vaccines against diseases such as measles , polio, and chicken pox are based on this principle.

In the late nineteenth century, a scientific debate was waged between the German physician Paul Ehrlich (18541915) and the Russian zoologist Élie Metchnikoff (18451916). Ehrlich and his followers believed that proteins in the blood, called antibodies, eliminated pathogens by sticking to them; this phenomenon became known as humoral immunity. Metchnikoff and his students, on the other hand, noted that certain white blood cells could engulf and digest foreign materials: this cellular immunity, they claimed, was the real way the body fought infection.

Modern immunologists have shown that both the humoral and cellular responses play a role in fighting disease. They have also identified many of the actors and processes that form the immune response.

The immune response recognizes and responds to pathogens via a network of cells that communicate with each other about what they have "seen" and whether it "belongs." These cells patrol throughout the body for infection, carried by both the blood stream and the lymph ducts, a series of vessels carrying a clear fluid rich in immune cells.

The antigen presenting cells are the first line of the body's defense, the scouts of the immune army. They engulf foreign material or microorganisms and digest them, displaying bits and pieces of the invaderscalled antigensfor other immune cells to identify. These other immune cells, called T lymphocytes, can then begin the immune response that attacks the pathogen.

The body's other cells can also present antigens, although in a slightly different way. Cells always display antigens from their everyday proteins on their surface. When a cell is infected with a virus, or when it becomes cancerous, it will often make unusual proteins whose antigens can then be identified by any of a variety of cytotoxic T lymphocytes. These "killer cells" then destroy the infected or cancerous cell to protect the rest of the body. Other T lymphocytes generate chemical or other signals that encourage multiplication of other infection-fighting cells. Various types of T lymphocytes are a central part of the cellular immune response; they are also involved in the humoral response, encouraging B lymphocytes to turn into antibody-producing plasma cells.

The body cannot know in advance what a pathogen will look like and how to fight it, so it creates millions and millions of different lymphocytes that recognize random antigens. When, by chance, a B or T lymphocyte recognizes an antigen being displayed by an antigen presenting cell, the lymphocyte divides and produces many offspring that can also identify and attack this antigen. The way the immune system expands cells that by chance can attack an invading microbe is called clonal selection .

Some researchers believe that while some B and T lymphocytes recognize a pathogen and begin to mature and fight an infection, others stick around in the bloodstream for months or even years in a primed condition. Such memory cells may be the basis for the immunity noted by the ancient Chinese and by Thucydides. Other immunologists believe instead that trace amounts of a pathogen persist in the body, and their continued presence keeps the immune response strong over time.

Substances foreign to the body, such as disease-causing bacteria , viruses , and other infectious agents (known as antigens), are recognized by the body's immune system as invaders. The body's natural defenses against these infectious agents are antibodiesproteins that seek out the antigens and help destroy them. Antibodies have two very useful characteristics. First, they are extremely specific; that is, each antibody binds to and attacks one particular antigen. Second, some antibodies, once activated by the occurrence of a disease, continue to confer resistance against that disease; classic examples are the antibodies to the childhood diseases chickenpox and measles.

The second characteristic of antibodies makes it possible to develop vaccines. A vaccine is a preparation of killed or weakened bacteria or viruses that, when introduced into the body, stimulates the production of antibodies against the antigens it contains.

It is the first trait of antibodies, their specificity, that makes monoclonal antibody technology so valuable. Not only can antibodies be used therapeutically, to protect against disease; they can also help to diagnose a wide variety of illnesses, and can detect the presence of drugs, viral and bacterial products, and other unusual or abnormal substances in the blood.

Given such a diversity of uses for these disease-fighting substances, their production in pure quantities has long been the focus of scientific investigation. The conventional method was to inject a laboratory animal with an antigen and then, after antibodies had been formed, collect those antibodies from the blood serum (antibody-containing blood serum is called antiserum ). There are two problems with this method: It yields antiserum that contains undesired substances, and it provides a very small amount of usable antibody.

Monoclonal antibody technology allows the production of large amounts of pure antibodies in the following way. Cells that produce antibodies naturally are obtained along with a class of cells that can grow continually in cell culture . The hybrid resulting from combining cells with the characteristic of "immortality" and those with the ability to produce the desired substance, creates, in effect, a factory to produce antibodies that work around the clock.

A myeloma is a tumor of the bone marrow that can be adapted to grow permanently in cell culture. Fusing myeloma cells with antibody-producing mammalian spleen cells, results in hybrid cells, or hybridomas, producing large amounts of monoclonal antibodies. This product of cell fusion combined the desired qualities of the two different types of cells, the ability to grow continually, and the ability to produce large amounts of pure antibody. Because selected hybrid cells produce only one specific antibody, they are more pure than the polyclonal antibodies produced by conventional techniques. They are potentially more effective than conventional drugs in fighting disease, because drugs attack not only the foreign substance but also the body's own cells as well, sometimes producing undesirable side effects such as nausea and allergic reactions. Monoclonal antibodies attack the target molecule and only the target molecule, with no or greatly diminished side effects.

While researchers have made great gains in understanding immunity, many big questions remain. Future research will need to identify how the immune response is coordinated. Other researchers are studying the immune systems of nonmammals, trying to learn how our immune response evolved. Insects, for instance, lack antibodies, and are protected only by cellular immunity and chemical defenses not known to be present in higher organisms.

Immunologists do not yet know the details behind allergy, where antigens like those from pollen, poison ivy, or certain kinds of food make the body start an uncomfortable, unnecessary, and occasionally life-threatening immune response. Likewise, no one knows exactly why the immune system can suddenly attack the body's tissuesas in autoimmune diseases like rheumatoid arthritis, juvenile diabetes, systemic lupus erythematosus, or multiple sclerosis.

The hunt continues for new vaccines, especially against parasitic organisms like the malaria microbe that trick the immune system by changing their antigens. Some researchers are seeking ways to start an immune response that prevents or kills cancers. A big goal of immunologists is the search for a vaccine for HIV , the virus that causes AIDS . HIV knocks out the immune systemcausing immunodeficiencyby infecting crucial T lymphocytes. Some immunologists have suggested that the chiefly humoral response raised by conventional vaccines may be unable to stop HIV from getting to lymphocytes, and that a new kind of vaccine that encourages a cellular response may be more effective.

Researchers have shown that transplant rejection is just another kind of immune response, with the immune system attacking antigens in the transplanted organ that are different from its own. Drugs that suppress the immune system are now used to prevent rejection, but they also make the patient vulnerable to infection. Immunologists are using their increased understanding of the immune system to develop more subtle ways of deceiving the immune system into accepting transplants.

See also AIDS, recent advances in research and treatment; Antibody, monoclonal; Biochemical analysis techniques; BSE, scrapie and CJD: recent advances in research; History of immunology; Immunochemistry; Immunodeficiency disease syndromes; Immunodeficiency diseases; Immunodeficiency; Immunogenetics; Immunological analysis techniques; Immunology, nutritional aspects; Immunosuppressant drugs; Infection and resistance; Laboratory techniques in immunology; Reproductive immunology; Transplantation genetics and immunology

views updated

Immunology

Immunology is the study of how the body responds to foreign substances and fights off infection and other disease . Immunologists study the molecules, cells, and organs of the human body that participate in this response.


History of immunology

No one knows when humans first noticed that they are better at fighting a disease the second time they get it; Chinese documents from 5,000 b.c. mention the fact. In 430 b.c., the Greek historian Thucydides (?-411 b.c.) mentioned the great plague that swept through Athens, and how those who survived it (including Thucydides himself) could tend to the sick without worrying about catching it again.

But the beginnings of our understanding of immunity date to 1798, when the English physician Edward Jenner (1749-1823) published a report that people could be protected from deadly smallpox by sticking them with a needle dipped in the pus from a cowpox boil. The great French biologist and chemist Louis Pasteur (1822-1895) theorized that such immunization protects people against disease by exposing them to a version of a microbe that is harmless but is enough like the disease-causing organism , or pathogen, that the immune system learns to fight it. Modern vaccines against diseases such as measles, polio, and chicken pox are based on this principle.

In the late nineteenth century, a scientific debate was waged between the German physician Paul Ehrlich (1854-1915) and the Russian zoologist Elie Metchnikoff (1845-1916). Ehrlich and his followers believed that proteins in the blood , called antibodies, eliminated pathogens by sticking to them; this phenomenon became known as humoral immunity. Metchnikoff and his students, on the other hand, noted that certain white blood cells could engulf and digest foreign materials: this cellular immunity, they claimed, was the real way the body fought infection.

Modern immunologists have shown that both the humoral and cellular responses play a role in fighting disease. They have also identified many of the actors and processes that form the immune response.


Friend or foe?

The immune response recognizes and responds to pathogens via a network of cells that communicate with each other about what they have "seen" and whether it "belongs." These cells patrol throughout the body for infection, carried by both the blood stream and the lymph ducts, a series of vessels carrying a clear fluid rich in immune cells.

The antigen presenting cells are the first line of the body's defense, the scouts of the immune army. They engulf foreign material or microorganisms and digest them, displaying bits and pieces of the invaders—called antigens—for other immune cells to identify. These other immune cells, called T lymphocytes, can then begin the immune response that attacks the pathogen.

The body's other cells can also present antigens, although in a slightly different way. Cells always display antigens from their everyday proteins on their surface. When a cell is infected with a virus , or when it becomes cancerous, it will often make unusual proteins whose antigens can then be identified by any of a variety of cytotoxic T lymphocytes. These "killer cells" then destroy the infected or cancerous cell to protect the rest of the body. Other T lymphocytes generate chemical or other signals that encourage multiplication of other infection-fighting cells. Various types of T lymphocytes are a central part of the cellular immune response; they are also involved in the humoral response, encouraging B lymphocytes to turn into antibody-producing plasma cells.


Selecting disease fighters

The body cannot know in advance what a pathogen will look like and how to fight it, so it creates millions and millions of different lymphocytes that recognize random antigens. When, by chance, a B or T lymphocyte recognizes an antigen being displayed by an antigen presenting cell, the lymphocyte divides and produces many offspring that can also identify and attack this antigen. The way the immune system expands cells that by chance can attack an invading microbe is called clonal selection .

Some researchers believe that while some B and T lymphocytes recognize a pathogen and begin to mature and fight an infection, others stick around in the bloodstream for months or even years in a primed condition. Such memory cells may be the basis for the immunity noted by the ancient Chinese and by Thucydides. Other immunologists believe instead that trace amounts of a pathogen persist in the body, and their continued presence keeps the immune response strong over time.


Advances in immunology—monoclonal antibody technology

Substances foreign to the body, such as diseasecausing bacteria , viruses, and other infectious agents (known as antigens), are recognized by the body's immune system as invaders. The body's natural defenses against these infectious agents are antibodies—proteins that seek out the antigens and help destroy them. Antibodies have two very useful characteristics. First, they are extremely specific; that is, each antibody binds to and attacks one particular antigen. Second, some antibodies, once activated by the occurrence of a disease, continue to confer resistance against that disease; classic examples are the antibodies to the childhood diseases chickenpox and measles.

The second characteristic of antibodies makes it possible to develop vaccines. A vaccine is a preparation of killed or weakened bacteria or viruses that, when introduced into the body, stimulates the production of antibodies against the antigens it contains.

It is the first trait of antibodies, their specificity, that makes monoclonal antibody technology so valuable. Not only can antibodies be used therapeutically, to protect against disease; they can also help to diagnose a wide variety of illnesses, and can detect the presence of drugs, viral and bacterial products, and other unusual or abnormal substances in the blood.

Given such a diversity of uses for these diseasefighting substances, their production in pure quantities has long been the focus of scientific investigation. The conventional method was to inject a laboratory animal with an antigen and then, after antibodies had been formed, collect those antibodies from the blood serum (antibody-containing blood serum is called antiserum). There are two problems with this method: It yields antiserum that contains undesired substances, and it provides a very small amount of usable antibody.

Monoclonal antibody technology allows the production of large amounts of pure antibodies in the following way. Cells that produce antibodies naturally are obtained along with a class of cells that can grow continually in cell culture. The hybrid resulting from combining cells with the characteristic of "immortality" and those with the ability to produce the desired substance, creates, in effect, a factory to produce antibodies that works around the clock.

A myeloma is a tumor of the bone marrow that can be adapted to grow permanently in cell culture. Fusing myeloma cells with antibody-producing mammalian spleen cells, results in hybrid cells, or hybridomas, producing large amounts of monoclonal antibodies. This product of cell fusion combined the desired qualities of the two different types of cells: the ability to grow continually, and the ability to produce large amounts of pure antibody. Because selected hybrid cells produce only one specific antibody, they are more pure than the polyclonal antibodies produced by conventional techniques. They are potentially more effective than conventional drugs in fighting disease, since drugs attack not only the foreign substance but the body's own cells as well, sometimes producing undesirable side effects such as nausea and allergic reactions. Monoclonal antibodies attack the target molecule and only the target molecule, with no or greatly diminished side effects.


Goals for the future

While researchers have made great gains in understanding immunity, many big questions remain. Future research will need to identify how the immune response is coordinated. Other researchers are studying the immune systems of non-mammals, trying to learn how our immune response evolved. Insects , for instance, lack antibodies, and are protected only by cellular immunity and chemical defenses not known to be present in higher organisms.

Immunologists do not yet know the details behind allergy , where antigens like those from pollen, poison ivy, or certain kinds of food make the body start an uncomfortable, unnecessary, and occasionally life-threatening immune response. Likewise, no one knows exactly why the immune system can suddenly attack the body's tissues—as in autoimmune diseases like rheumatoid arthritis , juvenile diabetes, systemic lupus erythematosus, or multiple sclerosis.

The hunt continues for new vaccines, especially against parasitic organisms like the malaria microbe that trick the immune system by changing their antigens. Some researchers are seeking ways to start an immune response that prevents or kills cancers. A big goal of immunologists is the search for a vaccine for HIV, the virus that causes AIDS . HIV knocks out the immune system—causing immunodeficiency—by infecting crucial T lymphocytes. Some immunologists have suggested that the chiefly humoral response raised by conventional vaccines may be unable to stop HIV from getting to lymphocytes, and that a new kind of vaccine that encourages a cellular response may be more effective.

Researchers have shown that transplant rejection is just another kind of immune response, with the immune system attacking antigens in the transplanted organ that are different from its own. Drugs that suppress the immune system are now used to prevent rejection, but they also make the patient vulnerable to infection. Immunologists are using their increased understanding of the immune system to develop more subtle ways of fooling the immune system into accepting transplants.

See also Antibody and antigen.


Resources

books

Joneja, Janice M. Vickerstaff, and Leonard Bielory. Understanding Allergy, Sensitivity, and Immunity: a Comprehensive Guide. New Brunswick: Rutgers University Press, 1990.

Paul, William E., ed. Immunology Recognition and Response. New York: W. H. Freeman and Company, 1991.

Porter, Roy, and Marilyn Ogilvie, eds. The Biographical Dictionary of Scientists. Vol. 2. Oxford: Oxford University Press, 2000.

Richman, D.D., and R.J. Whitley. Clinical Virology. 2nd ed. Washington: American Society for Microbiology, 2002.

Rose, N.R. Manual of Clinical Laboratory Immunology. 4th ed. Washington: American Society for Microbiology, 2002.

periodicals

Cimons, M. "New Prospects on the HIV Vaccine Scene." ASM News no. 68 (January 2002): 19-22.

Erickson, Deborah. "Industrial immunology: Antibodies May Catalyze Commercial Chemistry." Scientific American (September 1991): 174-175.

"Life, Death and the Immune System." Special issue, Scientific American (September 1993): 52-144.


Kenneth B. Chiacchia

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Autoimmunity

—An aberrant immune response that attacks the body's own tissues.

Cellular immunity

—The arm of the immune system that uses cells and their activities to kill pathogens, infected cells, and cancer cells.

Clonal selection

—The process whereby one or a few immune cells that by chance recognize an antigen multiply when the antigen is present in the body.

Humoral immunity

—The arm of the immune system that uses antibodies and other chemicals to clear pathogens from the body and to kill infected or cancerous cells.

Immunodeficiency

—A condition where the immune response is weak or incomplete, allowing pathogens to cause disease more easily. AIDS is a kind of immunodeficiency.

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im·mu·nol·o·gy / ˌimyəˈnäləjē/ • n. the branch of medicine and biology concerned with immunity. DERIVATIVES: im·mu·no·log·ic / ˌimyənəˈläjik; iˌmyoō-/ adj. im·mu·no·log·i·cal / ˌimyənəˈläjikəl; iˌmyoō-/ adj. im·mu·no·log·i·cal·ly / ˌimyənəˈläjik(ə)lē; iˌmyoō-/ adv. im·mu·nol·o·gist / -jist/ n.

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immunology Study of immunity and allergy. It is concerned with the preventing disease by vaccination – active immunity; or by injections of antibodies – passive immunity. Allergic reactions result from an overactive response to harmless foreign substances such as dust, rather than to infective organisms.

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immunology (im-yoo-nol-ŏji) n. the study of immunity and all of the phenomena connected with the defence mechanisms of the body.
immunological adj.

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