Antibody

From ArticleWorld

An antibody is a protein-based molecule that is produced by the immune system in order to tag pathogens for later destruction. Antibodies are also known as “immunoglobulins” and are made by plasma cells. Plasma cells come from the B-cell line of lymphocytes. Antibodies are made in order to bind to “antigens” or specific identifying molecules on the surface of cells, bacteria, fungi or viruses.

Types

There are five different categories of antibodies. They are called IgG, IgA, IgM, IgD and IgE isotypes. Each B-cell can make several classes of antibodies at once. Different types of antibodies are made slightly differently from one another and perform different functions.

The IgG antibody is made from two heavy chains of proteins and two light chains of protein. Heavy chains are about 500 amino acids long, while light chains are about 200 amino acids long. The chains are connected into a “Y” shape by disulfide molecular bonds.

The IgG antibody is the most common and is found in both blood and tissues. IgG antibodies can pass through the placenta and provide temporary protection to the newborn. IgG antibodies can bind to nearly every kind of pathogen.

IgA antibodies make up about 20% of all antibodies. These antibodies are secreted by the mucosal cells into the gastrointestinal tract and are called the “secretory antibodies”. Saliva, breast milk and tears all contain IgA antibodies. Pathogens that come in contact with a human via the mucous membranes are dealt with first by the IgA antibodies.

IgM antibodies are very large, with up to 5-6 Y-shaped monomers connected together. Each Y-shaped monomer can bind two antigens each, so that an IgM antibody can technically bind up to 12 antigens at once. IgM is found almost exclusively in the bloodstream because it is too large to traverse the lining of the blood vessels and enter the tissues. The IgM antibody has the natural ability to bind to an antigen that it hasn’t previously been in contact with.

IgD antibodies comprise only 1% of all antibodies. It remains on the cell membranes of B-cells and mark the degree of the B-cell’s maturity. Some believe that IgD antibodies are involved with differentiating between normal plasma B-cells and “memory” cells that retain the ability to recall previously-designed antibodies.

IgE antibodies are found on the surfaces of cells involved in the allergic response. They are also involved in the immune response toward pathogenic worms and other parasites. IgE antibodies can, like the IgA antibodies, be found in bodily secretions.