Difference Between Antigen and Antibody

The key difference between antigen and antibody is that antigen is any substance that induces the immune system to produce antibodies against it while antibody is a Y shaped immunoglobulin protective protein that is capable of binding with antigens in order to neutralize them.

The core understanding of immunology, as well as some aspects of microbiology, pathology, and dermatology, relies on the understanding of the basic concepts of antigen-antibody reactions. These are the building blocks of vast bases for knowledge and newly developing technologies to combat varied amounts of diseases.


1. Overview and Key Difference
2. What is an Antigen
3. What is an Antibody
4. Similarities Between Antigen and Antibody
5. Side by Side Comparison – Antigen vs Antibody in Tabular Form
6. Summary

What is an Antigen?

An antigen is a substance that creates a cascade of activities prompting an immune response when introduced to the body. These substances can be molecules like proteins or cells like bacteria. They can also be pollens, toxins, viruses, etc. Moreover, proteins, peptides, and polysaccharides are their building blocks.

Figure 01: Antigen and Antibody

There are two main varieties of antigens. One is the self-antigen (autoantigens), and the other is nonself antigen (foreign antigens). Usually, self-antigens do not provoke reactions from the immune system, but they can usually lead to an immune response as detailed in autoimmune diseases. Each antigen has an epitope or an area on the antigen that reacts with the other components or histocompatibility area. Thus, this area acts as a key to lock in the antibody.

What is an Antibody?

An antibody is a varied size protein molecule, which is present in the blood and secretions and acts upon antigens to produce the ultimate resolution of inactivation or destruction. B cells produce antibodies. Then, they become differentiated into plasma cells as a response to the immune system. Antibodies are proteins that resemble “Y” shape and the two hands of the “Y” contain paratopes or locks on the antibody which can attach to the key of the epitope of antigens.

Figure 02: Types of Antibodies

There are main five subclasses of antibodies that differ from each other due to the number of heavy and light chains. Also, they differ in their functions as to the location, transplacental transportation, and to write another spooky episode. Those five antibody isotypes are IgA, IgD, IgE, IgG, and IgM.

What are the Similarities Between Antigen and Antibody?

  • Antigens bind with antibodies.
  • Thus, antibodies are capable of attacking antigens and neutralizing them.
  • All antibodies and some antigens are proteins.
  • Besides, both are paramount for immunology.
  • Moreover, both partake in autoimmune diseases, and the end result is the same.
  • They are microscopic particles.

What is the Difference Between Antigen and Antibody?

An antigen is a substance that can induce the immune system to produce antibodies against it while an antibody is a protective protein produced by the B cells of the immune system in order to attack antigens. So, this is the key difference between antigen and antibody. Furthermore, a significant difference between antigen and antibody is their composition. That is; the antibodies are purely made up of proteins, but the antigens have combinations of  polysaccharides as well.

Moreover, an important difference between antigen and antibody is that, in antigen-antibody interaction, antigens act as the key, whereas antibodies act as the lock. Besides, antigens can be cells, but antibodies are never cells. Therefore, we can consider this too as a difference between antigen and antibody. Additionally, there are mainly two types of antigens as self-antigens (autoantigens) and non-self antigens (foreign antigens). But, antibodies have five main subcategories: IgA, IgD, IgE, IgG, and IgM according to the proteins constructs.

Summary – Antigen vs Antibody

An antigen is a substance that is capable of inducing the immune system to produce antibodies against it. Examples of antigens are pollens, viruses, bacteria, protozoans, toxins, proteins, and spores. Furthermore, there are two types of antigens namely foreign antigens or autoantigens. Foreign antigens originate outside the body while autoantigens originate within the body. On the other hand, an antibody is an immunoglobulin protein produced by the immune system. They are Y shaped proteins. They are capable of binding with antigens and destroy or neutralize them in order to stop the immune reactions. Antigen-antibody interaction is specific, and they bond with each other when their structural shapes are complementary. Here, paratope of the antibody binds with the epitope of the antigen. Thus, this is the summary of the difference between antigen and antibody.


1. “Antigen.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 7 June 2016, Available here.
2. “Antibody.” Wikipedia, Wikimedia Foundation, 19 Apr. 2019, Available here.

Image Courtesy:

1. “Antibody” By Fvasconcellos 19:03, 6 May 2007 (UTC) – Color version of Image:Antibody.png, originally a Work of the United States Government (Public Domain) via Commons Wikimedia
2. “Figure 42 03 02” By CNX OpenStax – (CC BY 4.0) via Commons Wikimedia