Antibody Applications

The uses for antibodies

Antibodies are a specific type of protein. These specialized Y-shaped proteins bind to antigens, which can stimulate an immune response (Figure 1).

Today, antibodies are utilized in antigen testing kits and biologics. Antibodies are also an integral tool used in several research methods:

• Western blots
• Chromatin immunoprecipitation (ChIP)
• Enzyme-linked immunosorbent assay (ELISA)

The function of antibodies

Antibodies are secreted into the blood and mucosa, which facilitates three biological functions:

• Neutralization occurs when the antibody binds to and inactivates the foreign substance, such as pathogens and toxins
• Activation of complement system facilitates the destruction of bacterial cells
• Opsonization of foreign substances facilitated by phagocytic cells

What is the anatomy of an antibody?

Antibodies are made up of two identical light chains (yellow) and two identical heavy chains (blue) (Figure 2).

Light chains: Have one variable domain (VL) and one constant domain (CL).

Heavy chains: Have one variable domain (VH) and three or four constant (CH) domains.

These variable domains are encoded by DNA. There are a countless number of combinations of these regions to create a diverse pool of antibodies with highly specific antigen-binding sites. Finding the most effective antigen-binding sequences can be used to research potential therapies and/or new diagnostic tests.

The difference between light and heavy chain is that the light chain is the small polypeptide subunit of an antibody while the heavy chain is the large polypeptide unit of an antibody.

The five types of antibodies

There are five types of heavy chain constant regions found in antibodies. Each antibody type is classified as IgG, IgM, IgA, IgD, or IgE. A summarized list of each antibody type and known function is described in Table 1.

Table 1. The five types of antibodies

IgG		Most common type of antibody found in blood circulation Activates the classical pathway of the complement system Binds and neutralizes toxins (bacterial and viral)
IgM		Largest antibody type First antibody to appear in the response to initial exposure to antigen Transiently increases
IgA		Most abundant antibody in the body Responsible for the immune function of mucous membranes
IgD		Function largely remains a mystery Co-expressed with IgM in B cells
IgE		Least abundant antibody Responsible for immune response against parasites Involved in allergies