Inside of you are proteins whose job is to fight against infections. Antibodies are these proteins, also called immunoglobulins, or Ig, because they are globulin proteins and are part of your immune system. Globulin proteins are a family or type of protein that has a similar structure.
How Are They Structured?
There are three kinds of globulin proteins, named alpha, beta and gamma after the first three letters of the Greek alphabet. All antibodies are gamma globulins. As explained by Dr. P.J. Delves, of the Department of Immunology and Molecular Pathology, University College of London, they all have two heavy chains and two light chains, the difference being in a chain's molecular weight. There are five classes of antibodies; this has been determined by the type of heavy chain an antibody has, according to Merck.com.
IgM
IgM is the first class of antibody that your immune system will make when it is responding to a foreign antigen, which is defined as any substance that causes your immune system to respond. When the IgM antibody is traveling in your bloodstream, it travels as a pentamer; this means five IgM antibodies are traveling together, with a J, or joining, chain holding them so they are joined as one, making this the largest antibody. It is very important in the fight against viruses and bacteria and is the first antibody that an infant makes, according to the "Introduction to Microbiology."
IgA
IgA is the class of antibody in your tears and saliva, as well as in the secretions of your intestines, respiratory and genital tracts. Its purpose is to prevent viruses and bacteria from being able to attach to the mucous membranes that form the lining of these tracts. Two IgA antibodies travel together, with a J chain holding them. But this antibody also has what is called a secretory component, which helps it pass through the mucous membrane and protects it from being destroyed in your intestines. IgA is also found in colostrum, the initial breast milk that the baby gets during breastfeeding. It is very important in protecting the infant's intestinal tract from infections, the "Introduction to Microbiology" indicates.
IgD
Scientists are not clear on the purpose of this antibody. They know that it is less than 1 percent of all antibodies. And they also know that it is the main one found on the cells that make all of your antibodies.
IgG
IgG is the main antibody that responds the second time you are exposed to a foreign antigen, and this type makes up at least 75 percent of all of the antibodies in your body. It is also the only one that can cross the mother's placenta. Because it responds to a second exposure, it "knows" what the mother has been exposed to and, therefore, protects the baby against it.
IgE
This antibody is on the surface of the white blood cells called eosinophils and basophils, and on the surface of cells called mast cells. Whenever an antigen binds to IgE, those cells release substances, such as histamine, to destroy that antigen. This is why IgE is responsible for your body's allergic reactions. But it also protects you against parasites, like worms, because it will cause the eosinophils to release enzymes to destroy them, according to the "Introduction to Microbiology."
References
- "Introduction to Microbiology"; John Ingraham, Catherine Ingraham; 1995
- "The Merck Manual: Components of the Immune System."
