Antibodies are a type of blood protein that the body produces in response to a particular antigen. They may also be referred to as immunoglobulin.
When the body detects an antigen, white blood cells bind to it. When B cells, a type of white blood cell, bind to an antigen, they multiply and produce antibodies.
The antibodies can then bind to the specific antigen and eliminate it from the body. However, while the antigen leaves the body, antibodies remain in the body and offer continued protection from that type of antigen for a set period.
There are five classes of antibodies, which are separated based on their location. Each class is assigned a letter, which is attached to the abbreviation for immunoglobulin (Ig).
- IgA: found in tears, saliva, breast milk, mucus, and intestinal fluid
- IgD: found on the surface of B cells
- IgE: primarily found in the lungs, skin, and mucus membranes; helpful for fighting off allergic reactions
- IgG: the most common antibody; found in tissue fluids and blood
- IgM: found in the lymph system and blood
Based on their location, these antibodies play important roles in different infections. For example, IgG helps protect the body from bacterial and viral infections, whereas IgA protects against inhaled and ingested pathogens.