Table of ContentsView AllTable of ContentsImmunoglobulin G (IgG)Immunoglobulin A (IgA)Immunoglobulin M (IgM)Immunoglobulin E (IgE)Immunoglobulin D (IgD)Antibody Testing
Table of ContentsView All
View All
Table of Contents
Immunoglobulin G (IgG)
Immunoglobulin A (IgA)
Immunoglobulin M (IgM)
Immunoglobulin E (IgE)
Immunoglobulin D (IgD)
Antibody Testing
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Immunoglobulin Isotypes
While there are only five main types of antibodies, each can have a different binding site that matches a specific antigen. Your body can produce an infinite number of binding sites to bind to antigens.
Immunoglobulin G (IgG) accounts for around 75% of all antibodies in the human body. Depending on the antigen, IgG can either tag a pathogen so other immune cells and proteins will recognize it, or it can activate the complement system to directly destroy the microorganism.
IgG can sometimes trigger an undesirable response in people withautoimmune diseases, in which the immune system inadvertently attacks its own cells and tissues.
IgA is one of the body’s first-line defenses against infection. It binds to pathogens to tag them for destruction and prevents them from sticking to the epithelium, which lines the body’s tissues.
IgA is also associated with hypersensitive reactions in people withceliac diseaseand several other autoimmune disorders.
What Are Autoantibodies?An autoantibody is an antibody directed against the body’s cells. Antibodies are designed to attack invading pathogens, like viruses and bacteria. Autoantibodies occur when the immune system becomes confused and mounts an assault on the body’s own proteins. Autoantibodies are involved in autoimmune diseases like rheumatoid arthritis, type 1 diabetes, multiple sclerosis, and lupus.
What Are Autoantibodies?
An autoantibody is an antibody directed against the body’s cells. Antibodies are designed to attack invading pathogens, like viruses and bacteria. Autoantibodies occur when the immune system becomes confused and mounts an assault on the body’s own proteins. Autoantibodies are involved in autoimmune diseases like rheumatoid arthritis, type 1 diabetes, multiple sclerosis, and lupus.
In addition to activating the immune response, a subset of IgM helps B cells “remember” a pathogen after it has been destroyed. If you were to become re-exposed to the pathogen later, your immune system should respond more quickly due to your memory B cells.
When IgE binds to an allergen, it triggers a cascade of events.Basophilsandmast cells, which are subtypes of WBCs, degranulate (break open) and releasehistamine, an inflammatory compound, into the bloodstream. It is histamine that is responsible for many of the most commonsymptoms of allergy.
IgE also helps to protect the body from parasitic infections, including helminths (parasitic worms).
Immunoglobulin D (IgD) is important in the early stages of the immune response. Unlike other antibodies, it does not actively circulate but instead binds to B cells to instigate the immune response. As a signaling antibody, IgD helps incite the release of front-line IgM to fight disease and infection.
IgD accounts for only around 0.25% of antibodies in the human body. Despite its vital role in “kick-starting” the immune response, IgD is arguably the least understood antibody, with little known about how it might participate in other parts of the immune system.
Because immunoglobulins are matched to a specific pathogen, they can be used to diagnose some diseases based on their unique structure. Antibody tests are used to detect disease-specific antibodies in a blood sample.
Antibody tests are available to diagnose (or help diagnose) a wide variety of infectious and autoimmune diseases, including:
Antibody tests do not detect the actual pathogens that cause an infection—they detect the antibodies that are produced in response to the infection. A positive result means “yes,” the test has detected the antibody or antigen. A negative result means “no,” while borderline results are considered inconclusive.
Depending on the disease, it may take time for enough antibodies to be produced to reach detectable levels. If it’s done too soon, during the earlywindow period, the test may deliver a false negative result.
And some disorders are associated with a deficiency, not from a specific IgG. For example,primary immunodeficiency disease (PID)is diagnosed with a deficiency of total IgG.
An antibody test can confirm that an infection has taken place, as with COVID-19 or HIV, although it cannot tell you when.
Sometimes, immunoglobulin levels can be used to characterize the stage of an infection. Because IgM levels usually increase before the IgG response kicks in, a disease-specific IgM and IgG test can help determine whether an infection has occurred recently. For example, herpes simplex is an infection for whichIgMandIgGtests can help determine the timing of the infection.
In people with allergies, IgE tests can be used to confirm that an allergic response has occurred.
Summary
The body has five different types of antibodies, also known as immunoglobulins. IgA, IgD, IgG, IgE, and IgM are different immunoglobulin isotypes.
9 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Janeway C.Immunobiology. Garland Publishing. Print.Oncohema Key.The chemistry, structure, and function of immunoglobulins.Vidarsson G, Dekkers G, Rispens T.IgG subclasses and allotypes: from structure to effector functions.Frontiers Immunol.2015:5: 520. doi:10.3389/fimmu.2014.00520Thomas H.Unlocking the secrets of IgA.Nat Rev Gastroenterol Hepatol. 2018;15(7):389. doi:10.1038/s41575-018-0036-3Heyman B, Shulman, MJ.Structure, function, and production of immunoglobulin M (IgM).Encyclopedia Immunobiol. 2016;2016;1-14. doi:10.1016/B978-0-12-374279-7.05001-3Sutton BJ, Davies AM, Bax HJ, Karagiannis SN.IgE antibodies: From structure to function and clinical translation.Antibodies (Basel). 2019;8(1):19. doi:10.3390/antib8010019Mukai K, Tsai M, Starkl P, Marichal T, Galli SJ.IgE and mast cells in host defense against parasites and venoms.Semin Immunopathol. 2016;38(5):581-603. doi:10.1007/s00281-016-0565-1Mayo Clinic Laboratories.Immunoglobulin D (IgD), Serum - Clinical & Interpretive.American Sexual Health Association.Diagnosing Herpes.
9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Janeway C.Immunobiology. Garland Publishing. Print.Oncohema Key.The chemistry, structure, and function of immunoglobulins.Vidarsson G, Dekkers G, Rispens T.IgG subclasses and allotypes: from structure to effector functions.Frontiers Immunol.2015:5: 520. doi:10.3389/fimmu.2014.00520Thomas H.Unlocking the secrets of IgA.Nat Rev Gastroenterol Hepatol. 2018;15(7):389. doi:10.1038/s41575-018-0036-3Heyman B, Shulman, MJ.Structure, function, and production of immunoglobulin M (IgM).Encyclopedia Immunobiol. 2016;2016;1-14. doi:10.1016/B978-0-12-374279-7.05001-3Sutton BJ, Davies AM, Bax HJ, Karagiannis SN.IgE antibodies: From structure to function and clinical translation.Antibodies (Basel). 2019;8(1):19. doi:10.3390/antib8010019Mukai K, Tsai M, Starkl P, Marichal T, Galli SJ.IgE and mast cells in host defense against parasites and venoms.Semin Immunopathol. 2016;38(5):581-603. doi:10.1007/s00281-016-0565-1Mayo Clinic Laboratories.Immunoglobulin D (IgD), Serum - Clinical & Interpretive.American Sexual Health Association.Diagnosing Herpes.
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Janeway C.Immunobiology. Garland Publishing. Print.Oncohema Key.The chemistry, structure, and function of immunoglobulins.Vidarsson G, Dekkers G, Rispens T.IgG subclasses and allotypes: from structure to effector functions.Frontiers Immunol.2015:5: 520. doi:10.3389/fimmu.2014.00520Thomas H.Unlocking the secrets of IgA.Nat Rev Gastroenterol Hepatol. 2018;15(7):389. doi:10.1038/s41575-018-0036-3Heyman B, Shulman, MJ.Structure, function, and production of immunoglobulin M (IgM).Encyclopedia Immunobiol. 2016;2016;1-14. doi:10.1016/B978-0-12-374279-7.05001-3Sutton BJ, Davies AM, Bax HJ, Karagiannis SN.IgE antibodies: From structure to function and clinical translation.Antibodies (Basel). 2019;8(1):19. doi:10.3390/antib8010019Mukai K, Tsai M, Starkl P, Marichal T, Galli SJ.IgE and mast cells in host defense against parasites and venoms.Semin Immunopathol. 2016;38(5):581-603. doi:10.1007/s00281-016-0565-1Mayo Clinic Laboratories.Immunoglobulin D (IgD), Serum - Clinical & Interpretive.American Sexual Health Association.Diagnosing Herpes.
Janeway C.Immunobiology. Garland Publishing. Print.
Oncohema Key.The chemistry, structure, and function of immunoglobulins.
Vidarsson G, Dekkers G, Rispens T.IgG subclasses and allotypes: from structure to effector functions.Frontiers Immunol.2015:5: 520. doi:10.3389/fimmu.2014.00520
Thomas H.Unlocking the secrets of IgA.Nat Rev Gastroenterol Hepatol. 2018;15(7):389. doi:10.1038/s41575-018-0036-3
Heyman B, Shulman, MJ.Structure, function, and production of immunoglobulin M (IgM).Encyclopedia Immunobiol. 2016;2016;1-14. doi:10.1016/B978-0-12-374279-7.05001-3
Sutton BJ, Davies AM, Bax HJ, Karagiannis SN.IgE antibodies: From structure to function and clinical translation.Antibodies (Basel). 2019;8(1):19. doi:10.3390/antib8010019
Mukai K, Tsai M, Starkl P, Marichal T, Galli SJ.IgE and mast cells in host defense against parasites and venoms.Semin Immunopathol. 2016;38(5):581-603. doi:10.1007/s00281-016-0565-1
Mayo Clinic Laboratories.Immunoglobulin D (IgD), Serum - Clinical & Interpretive.
American Sexual Health Association.Diagnosing Herpes.
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