Types of antibodies
There are five different types of immunoglobulins (IgG, IgM, IgD, IgA and IgE), which differ from each other by the type of constant region that their heavy or H chains have.
- The IgG or globulins are the antibodies most abundant of the blood (up to 85% immunoglobulins). They are monomeric. They are made up of two L chains and two gamma-type H chains to which oligosaccharide molecules bind. They participate in the secondary immune response, they are created in large quantities when they come into contact, for the second time, with the antigen.
They bind to antigens on the surface of microorganisms, promoting their phagocytosis, in addition to activating both the complement system and blood phagocytes (macrophages and microphages). If the antigens are toxins, they bind to them, neutralizing them.
They are the only antibodies that cross the placenta, immunizing the fetus against the antigens for which the mother is immune, providing defenses to the newborn during the first weeks of life. It is also in breast milk, and can pass through the intestinal cells of the newborn, making them the first and only defensive molecules in the embryo and newborn, providing passive immunity.
- The IgM are the first antibodies that are created at the first exposure to an antigen (primary immune response). It is located in the blood serum. These immunoglobulins are pentameric, composed of five monomers linked by bridges disulfide. Due to their high molecular weight, they cannot leave the blood vessels.
- The IgA are dimeric. They are found in secretions such as saliva, tears, breast milk, serum and the mucus that lines the interior of the respiratory system and the intestine.
- The IgE are monomeric. They are located in tissues. They are responsible for allergic reactions, since they induce the release of histamine.
- The IgD are monomeric. They are antibodies on the surface of B lymphocytes serving as receptors for specific antigens, with the function of antigen recognition.