Your immune system makes five types of antibodies, each of which works in a different way to protect your body from disease and infection.
Antibodies are special 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 eliminate them. Harmful infectious organisms are identified as invaders because of their antigens, which are different molecules on their surface. Each antibody your immune system produces binds to a specific antigen (with the right molecular shape) and then either destroys the pathogen or tags it so other immune cells can recognize it.
Antibodies are also called immunoglobulins (Ig). Immunity describes immunity and globulin describes protein. They are produced by B cells, a specific type of white blood cell (WBC) that originate in the bone marrow.
Although 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 create an infinite number of binding sites to bind to antigens.
Immunoglobulin G (IgG)
Immunoglobulin G (IgG) makes up about 75% of all antibodies in the human body. Depending on the antigen, IgG can tag the pathogen so that other immune cells and proteins can recognize it, or it can facilitate the release of toxins to directly destroy the microbe.
IgG sometimes triggers adverse reactions in people with autoimmune diseases, in which the immune system inadvertently attacks its own cells and tissues.
Types of Autoimmune Diseases
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 tissue.
IgA is one of the body’s first lines of defense against infection. It binds to pathogens to mark them for destruction and prevent them from adhering to epithelial cells within human tissues.
IgA has also been linked to allergic reactions in people with celiac disease and several other autoimmune diseases.
Test for celiac disease antibodies
Immunoglobulin M (IgM)
Immunoglobulin M (IgM) is also one of the first antibodies that the immune system recruits to fight infection. When the body first encounters an infectious organism, the amount of IgM increases rapidly and then decreases dramatically with the appearance of IgG antibodies. IgM is also produced by B cells and, when bound to pathogens, stimulates other antibodies and immune cells to function.
In addition to activating the immune response, a subset of IgM also helps B cells “remember” a pathogen after it has been destroyed. If you are exposed to a pathogen again in the future, your immune system should respond faster thanks to your memory B cells.
Immunoglobulin E (IgE)
Immunoglobulin E (IgE) is an antibody that causes allergic reactions, mainly in the lungs, skin, and mucous membranes. IgE (a harmless substance that induces allergic reactions) is produced by B cells secreted by lymph nodes or other lymphoid tissues located near the site of the allergen.
When IgE binds to an allergen, it triggers a chain of events. Basophils and mast cells are subtypes of WBC that degranulate (rupture) and release histamine, an inflammatory compound, into the blood. It is histamine that causes allergy symptoms.
IgE also helps protect the body from parasitic infections, including helminths (parasites).
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 provoke an immune response. As a signaling antibody, IgD helps stimulate the release of first-line IgM to fight disease and infection.
IgD only accounts for about 0.25% of human antibodies. Despite its crucial role in “priming” the immune response, IgD is arguably the least understood antibody, and little is known about how it participates in other parts of the immune system.
Because immunoglobulins are matched to specific pathogens, certain diseases can be diagnosed based on their unique structure. Antibody tests are used to detect disease-specific antibodies in blood samples.
Antibody tests can be used to diagnose (or help diagnose) a variety of infectious and autoimmune diseases, including:
- Celiac Disease (CD)
- Coronavirus disease
- coxsackie virus
- Cytomegalovirus (CMV)
- Epstein-Barr virus (EBV)
- Helicobacter pylori
- Lyme disease
- Mycoplasma pneumoniae
- Whooping cough (whooping cough)
- Primary Immunodeficiency Disease (PID)
- Rubella (German Measles)
- Chickenpox-shingles virus
- viral hepatitis
- West Nile virus
Antibody tests don’t detect the actual pathogen that caused the infection – they detect antibodies that are produced against the infection. A positive result means “yes” that the test has detected antibodies or antigens. Negative results mean “no”, while borderline results are considered indeterminate.
Depending on the disease, it may take a while before enough antibodies are produced to reach detectable levels. If done too early, the test could produce false negative results during the early window.
An antibody test can confirm that an infection has occurred, just like COVID-19 or HIV, although it cannot tell you when it happened.
Sometimes, immunoglobulin levels can be used to characterize the stage of infection. Because IgM levels often increase before the onset of an IgG response, disease-specific IgM and IgG tests can help determine if a recent infection has occurred. For example, herpes simplex is an infection, and IgM and IgG tests can help determine the timing of the infection.
In people with allergies, an IgE test can be used to confirm whether an allergic reaction has occurred. These tests can also be used as part of the diagnostic process to determine if IgE levels increase when you are intentionally exposed to an allergen.
blood tests to diagnose allergies
When taking an antibody test, it is important to remember that antibodies are produced in response to a disease or infection; they are not a disease or infection. In fact, some antigen tests can detect actual pathogens by their characteristic antigens.
Some diseases can be diagnosed with antibody or antigen tests. In other cases, only antibody or antigen tests are available.
Your healthcare provider or clinic can tell you the window period for infection so you can get accurate results.
Frequently Asked Questions
What is an antibody?
Your body has different types of antibodies, each containing a unique antigen that keeps you healthy. Antibodies are proteins made by the immune system to fight off viruses, bacteria, and other pathogens that can make you sick. Some antigens destroy pathogens, while others bind to pathogens and signal to alert the immune system to an invader that needs to attack.
What are autoantibodies?
Autoantibodies are antibodies that target cells of the body. Antibodies are designed to attack invading pathogens, such as viruses and bacteria. Autoantibodies arise when the immune system becomes confused and attacks proteins. Autoantibodies are associated with autoimmune diseases such as rheumatoid arthritis, type 1 diabetes, multiple sclerosis, and lupus.
What is the difference between IgA, IgD, IgG, IgE and IgM?
The body has five different types of antibodies, also called immunoglobulins. IgA, IgD, IgG, IgE and IgM are different immunoglobulin isotypes.
- Immunoglobulin A (IgA) is present in mucosal tissues and is the front line defense against infection. IgA binds to pathogens to label them for destruction from other antibodies. IgA is also associated with celiac disease and other autoimmune diseases.
- IgD binds to B cells to initiate an immune response.
- IgG works in two ways: it binds to the pathogen to alert other immune cells to attack it or promotes the release of toxins to destroy the invader. In people with autoimmune diseases, IgG triggers the onset of symptoms.
- IgE are antibodies that cause allergic reactions. IgE binds to allergens and triggers the release of histamine, which causes allergic symptoms. IgE also helps fight parasitic infections.
- IgM was one of the first antibodies used to fight infection. When it binds to pathogens, it prompts the release of other antibodies, such as IgG. IgM also acts as a memory bank for the immune system, recalling pathogens that have been destroyed. IgM helps provide immunity against diseases you already have or have been vaccinated against.
What are monoclonal antibodies?