Definition

• Antibodies are glycoproteins or molecules composed of proteins and carbohydrates. These glycoproteins are found in the blood and act against toxic agents, such as bacteria, fungi, parasites and viruses.
  
  

Immunoglobulins

• Antibodies belong to a large family of proteins called immunoglobulins (Ig). Your blood produces Ig in response to foreign substances called immunogens. By default, your Ig binds and assists the immunogens out of the body, for instance, by producing tears when dust particles enter your eyes.
  
  

Structure

• Each antibody consists of two identical chains of amino acids called polypeptides---pairs of "heavy" and "light" chain amino acids---forming a Y-shaped molecule. The proteins are located in the Y's arms and the stem consists of proteins with carbohydrate molecules.
  
  

Function

• Antibodies defend your body by binding with viruses, bacteria and allergens in a key-and-lock manner, rendering the foreign bodies inactive. Another important function of the antibodies is to provide a lasting immunity. For instance, you acquire permanent immunity to measles after contracting the disease.
  
  

Classification

• There are five main classifications of antibodies according to structure: immunoglobulins A (IgA), D (IgD), E (IgE), G (IgG) and M (IgM). The most abundant class of antibodies in your blood are the IgG (75 percent of blood serum). The IgA are found in body fluids such as saliva and tears. The IgM are effective bacteria killers that reside mostly in your blood. The protective function of IgD, located in your blood serum, is uncertain. The IgE are responsible for allergic reactions and protect your body against parasitic infections.