What Are the 5 Types of Antibodies?

Your immune system produces five types of antibodies, each of which has distinct methods of defending your body against disease and infection.

Antibodies are specialized Y-shaped proteins made by the immune system. They help fight disease by detecting viruses, bacteria, and other pathogens (disease-causing microorganisms) and working to destroy them. Harmful infectious organisms are identified as invaders due to their antigens, which are distinct molecules on their surface. Each antibody produced by your immune system binds to a specific antigen—with a fitted molecular shape—and then either destroys the pathogen or tags it so other immune cells will recognize it.

Samples for medical screening

Immunoglobulin Isotypes

Antibodies are also known as immunoglobulins (Ig). Immuno describes immunity and globulin describes protein. They are produced by B cells, a specific type of white blood cell (WBC) that originates in the bone marrow.

While there are only five main types of antibodies, each antibody can have a different binding site that matches a specific antigen. In fact, your body can produce an infinite number of binding sites to bind to antigens.

Immunoglobulin G (IgG)

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 promote the release of toxins to directly destroy the microorganism.

IgG can sometimes trigger an undesirable response in people with autoimmune diseases, in which the immune system inadvertently attacks its own cells and tissues.

Immunoglobulin A (IgA)

Immunoglobulin A (IgA) is primarily found in mucosal tissues, such as those in the mouth, vagina, and intestines, as well as in saliva, tears, and breast milk. It accounts for 15% of all antibodies in the human body and is produced by B cells and secreted from the lamina propria, a thin layer within mucosal 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 with celiac disease and several other autoimmune disorders.

Immunoglobulin A (IgM)

Immunoglobulin M (IgM) is also one of the first antibodies recruited by the immune system to fight infection. IgM populations rise very quickly when the body is first confronted with an infectious organism, and then they plummet as IgG antibodies take over. IgM is also produced by B cells and, when bound to a pathogen, will spur other antibodies and immune cells into action.

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.

Immunoglobulin E (IgE)

Immunoglobulin E (IgE) is the antibody responsible for the allergic response that is mostly found in the lungs, skin, and mucosal membranes. IgE is produced by B cells secreted by lymph nodes or other lymphoid tissues situated near the site of the allergen (a harmless substance that induces an allergic response).

When IgE binds to an allergen, it triggers a cascade of events. Basophils and mast cells, which are subtypes of WBCs, degranulate (break open) and release histamine, an inflammatory compound, into the bloodstream. It is histamine that is responsible for the symptoms of allergy.

IgE also helps to protect the body from parasitic infections, including helminths (parasitic worms).

Immunoglobulin D (IgD)

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.

Antibody Testing

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 early window period, the test may deliver a false negative result.

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 which IgM and IgG tests 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. These tests can also be used as part of the diagnostic process to determine whether IgE levels increase when you are intentionally exposed to an allergen.

A Word From Verywell

When taking an antibody test, it is important to remember that antibodies are produced in response to a disease or infection; they are not the disease or infection. There are, in fact, some antigen tests that can detect an actual pathogen by its signature antigen.

Some diseases can be diagnosed with an antibody or antigen test. In other cases, only an antibody or antigen test is available.

Your healthcare provider or clinic can tell you the window period for your infection so you can get accurate results.

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