The human blood contains five different types of antibodies, also known as immunoglobulins. They are IgG, IgA, IgM, IgD, and IgE, according to WebMD. The abbreviation Ig in its own refers to immunoglobulin, or antibody. Each antibody has a different function.
The IgG antibodies are the most plentiful in the body. Found in all body fluids, the IgG antibodies defend the body against invading bacteria and viruses, explains WebMD. They are also the smallest of all the antibodies in the body, which is why they move easily across cell membranes. This mobility allows the IgG to cross the placenta to provide protection to the fetus; it is the only antibody capable of doing so.
The largest antibody is the IgM antibodies, notes WebMD. Found in blood and lymph fluid, IgM is the first type of antibody produced in response to a bacterial or viral infection. The IgA antibodies prevent antigens from infecting cells or reaching the internal organs. They are present in saliva, mucus, tears and blood as well as in areas such as the digestive tract, nose, eyes, ears and vagina.
The IgE antibodies are responsible for allergic reactions. They trigger the body to react against allergens such as pollen and fungus spores. They also provide protection against parasitic worms. IgE is present in the skin, lungs and mucous membranes. IgD antibodies are present in small amounts in the blood. They are found on the surface membranes of B cells. These cells produce and release antibodies. Their role in immune response is not clear, says WebMD.