Human blood contains five main types of antibodies, also known as immunoglobulins or isotypes. These are classified based on their heavy chains and each plays a distinct role in the immune system's defense mechanisms.
The Five Antibody Isotypes
- IgG (Immunoglobulin G): This is the most abundant antibody, making up approximately 70-75% of all antibodies in the human body. It's found mainly in blood and tissue fluids and plays a crucial role in fighting off infections. [Source: Cleveland Clinic, Kyowa Kirin, MBL Life Science]
- IgA (Immunoglobulin A): While present as monomers in the blood, IgA forms dimers in mucosal secretions, like saliva and tears. It provides primary defense against pathogens at mucosal surfaces. [Source: Kyowa Kirin]
- IgM (Immunoglobulin M): Often the first antibody produced during an infection. It's a large antibody found primarily in the blood. [Source: Kyowa Kirin]
- IgD (Immunoglobulin D): Its function is less well understood compared to other isotypes, but it's believed to be involved in B cell activation and maturation. [Source: Kyowa Kirin]
- IgE (Immunoglobulin E): Primarily involved in allergic reactions and defense against parasitic infections. [Source: Kyowa Kirin]
It's important to note that while there are only five main isotypes, the body can produce an incredibly diverse range of antibodies—up to one quintillion unique antibodies— through variations within these isotypes. This allows the immune system to recognize and target a vast array of pathogens. [Source: National Institutes of Health]
The ABO blood group system, while relevant to blood transfusions, is a separate classification system related to antigens on red blood cells, not directly to the types of antibodies present in the blood. [Source: NHS, NCBI]
