What is an Antibody?

The term antibody is used to describe a protein that is produced by the immune system in response to the presence of a foreign substance, known as an antigen. Antigens can be found on the surface of bacteria, viruses, and other pathogens. They can also be found on the surface of normal cells, such as red blood cells. Antibodies are capable of binding to antigens in order to neutralize them or mark them for destruction.

Antibodies are produced by plasma cells, which are a type of white blood cell. Plasma cells originate from B lymphocytes (B cells) that have been activated by an antigen. Once activated, B cells divide and produce two types of cells: memory B cells and plasma cells. Memory B cells remain in the body and provide long-term immunity against infections by quickly producing antibodies when they encounter an antigen again. Plasma cells produce large amounts of antibodies that circulate in the bloodstream and bind to antigens.

Structure of Antibodies

Antibodies are Y-shaped proteins made up of four polypeptides. These include two identical shorter low-molecular-weight chains called light chains and two identical longer high-molecular-weight chains called heavy chains. The n-terminals of the proteins vary significantly from one antibody to the next and are called variable regions. These regions are involved in antigen binding. The specificity of the binding interaction between an antibody and an antigen is determined by the arrangement of amino acids in the variable regions. The other regions vary little from other antibodies within the same specie of organism and are hence called constant regions. The tips of the Y-shaped region, known as the Fab region (fragment antigen-binding region), are responsible for binding to the antigen. The Fc region (crystallizable fragment region), the base of the Y, binds to other elements of the immune system such as phagocytes, to remove antigens. Antigen binding occurs via a number of non-covalent bonds including hydrogen bonds, ionic bonds, hydrophobic interactions, and van der walls interactions. The shape of the antibody’s binding site matches the shape of the antigen’s epitope (the place where the antibody binds). This specificity allows antibodies to bind to their corresponding antigens with great precision.

Antibody. Source, Wikicommons

Antigens may have more than one epitope. If the antibody recognizes only one epitope on the antigen, the antibody is referred to as monoclonal. If the antibody recognizes several epitopes on the antigen, it is called a polyclonal antibody.

Function Of Antibodies

There are several key functions of antibodies that are essential to the proper functioning of the immune system. One of the most important roles of antibodies is to binding to antigens, which are foreign substances that invade the body. This binding process helps to neutralize and remove the antigens from the body. In addition, antibodies also play a role in activating the complement system, which is a group of proteins that work together to enhance the ability of white blood cells to destroy foreign invaders.

Another important function of antibodies is to provide immunity against specific diseases. When a person is first infected with a disease-causing agent, their immune system produces antibodies specific to that pathogen. These antibodies help protect the individual from future infection by that same pathogen. Vaccines work by exposing individuals to an attenuated form of a pathogen, which triggers an immune response and the production of disease-specific antibodies. The presence of these antibodies provides individuals with immunity against the disease should they ever come into contact with the live virus or bacteria.

The Role of Specific Antibodies

IgA Antibodies

IgA antibodies are a type of antibody that is found in mucous membranes and in body fluids such as saliva, tears, and breast milk. They provide protection against infections of the respiratory tract, digestive tract, and urinary tract.

IgM Antibodies

IgM antibodies are the largest and most complex of the five major types of antibodies. They are the first type of antibody to be made in response to an infection. IgM antibodies can circulate in the blood for up to six months and are responsible for protecting against bacteria and viruses.

IgG Antibodies

IgG antibodies are the most common type of antibody in the body. They are found in all body fluids and protect against both bacterial and viral infections. IgG antibodies can also cross the placenta to give protection to the developing baby.

IgD antibodies

IgD antibodies are found in the blood and lymph fluid. They bind to antigens on the surface of cells and trigger the release of substances that kill or disable the invading cells.

IgE antibodies

IgE antibodies are a type of antibody that is produced by the immune system in response to an allergen. IgE antibodies attach to mast cells and cause them to release histamine, which leads to the symptoms of allergies.


Antibodies play a vital role in protecting the body against infection and disease. Without them, we would be susceptible to every illness and pathogen that comes our way. Thankfully, our bodies are able to produce these important proteins when we need them.


  • Courtney Simons

    Dr. Courtney Simons has served as a food science researcher and educator for over a decade. He holds a Bachelor of Science in Food Science and a Ph.D. in Cereal Science from North Dakota State University.