Antibody, also known as an immunoglobulin, is a protein which is produced by the immune system of the body in order to kill harmful pathogens like bacteria, fungi, viruses and even chemicals. During an immune reaction B lymphocytes (a type of white blood cell) produce plasma cells which are specialized in producing antibody. Antigens from disease-producing agents like bacteria, viruses, etc. bind to specialized protein on their outer surface and stimulate them to produce large quantities of antibodies. The unique property of antibody is that it binds only to specific antigen. The potency of binding an antibody and antigen is known as affinity.
There are different types of antibodies present in blood – IgG, IgA, IgM, IgD and IgE. Each type of antibody has a definite method to destroy the pathogens and thus helps to protect the body against foreign agents. In pathological conditions like autoimmune disorder, sometimes antibodies erroneously consider healthy tissues as a foreign substance and kill them.