Immunoglobulin G (IgG) antibodies are proteins made by the body's natural defense system (immune system). They attack and destroy things that they recognize as different from the body's normal healthy tissues, such as bacteria and viruses.
IgG antibodies are found in all body fluids and are very important in fighting infections. They are the most common of the five major types of antibodies. IgG antibodies can cross the placenta in a pregnant woman to help protect the fetus.
WebMD Medical Reference from Healthwise