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Antigen vs antibody – what is the difference?

Antigen vs antibody - 3D illustration
3D illustration of antigen in the human body

What is the difference between Antigen vs antibody, and what role do they play in creating an effective vaccine? With the recent focus on the development of a COVID-19 vaccine there has been much talk of antigens and antibodies, often interchangeably, and little clarity on what they are – or the role they play in creating an effective vaccine. In this blog, we’ll cut through the jargon and discover the facts together.

Antigen

An antigen is any substance or organism that is unrecognized by our Immune system. It could be anything from bacteria to chemicals, to viruses … or even foods [1]. Antigens typically trigger an immune response, which may consist of an antibody (more on that later), and are classified by their origins [2]:

  • Exogenous: entering from outside the body
  • Endogenous: generated from within
  • Autoantigens: proteins targeted in autoimmune diseases
  • Neoantigens (or tumor antigens): resulting from tumor cells.
  • Native antigens: An antigen which will later be processed by an antigen-presenting cell

In some cases, these main types have subtypes – but we won’t get into an immunology lecture today. An antigen-presenting cell is a cell that processes and then presents the antigen to T-cells (a form of white blood cells), which can then ‘handle’ the antigen, often by killing the offending cell [3].

Your immune system has “memory” which allows the system to deal with the offending antigen much more quickly and efficiently the next time it is encountered.  Vaccines are designed to simulate that first encounter with an antigen and create a robust memory in case the offending agent reappears in the future. [4].

The importance of vaccines is covered in more detail here, but in short, antigens themselves are crucial in the development of vaccines. Generally, the vaccine consists of a potentially hostile antigen, in a very weak or inactive form.

Antibody

Antibodies are proteins that bind with the antigen in order to neutralize the latter – or make other elements of the immune system “aware” of their presence.  Antibody-producing cells are specifically designed to tackle one type of antigen; and your blood, bone marrow, lymph glands, and spleen will contain millions of them to ensure that every known antigen will be confronted by a corresponding antibody  [5].

Antibodies are secreted by B leukocytes (a form of white blood cell) and circulate in blood plasma either freely or attached to the surface of a B cell.  The B and T cells work in unison to identify and locate antigens, create the correct antibodies, and capture (kill/neutralize) the antigen [6].

A vaccine, by exposing the immune system to a new antigen, will “teach” antibodies the correct format in which to capture or tag that antigen.  When the actual disease antigen later enters the body, the immune system will rapidly respond with minimal discomfort and inconvenience.

Effective vaccination needs both

To summarize – an antigen is a disease agent (virus, toxin, bacterium parasite, fungus, chemical, etc) that the body needs to remove, and an antibody is a protein that binds to the antigen to allow our immune system to identify and deal with it.

Woman with adhesive bandage on her shoulder
Antigens and antibodies work in tandem when vaccinating

Don’t take this all for granted, though. As impressive as our immune system is, it’s far from perfect and needs our assistance to prevent harmful antigens from entering the body – through hand washing, face masks, and social distancing. Look after your body and it will look after you!

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References:

[1] M. Encyclopedia, “Antigen: MedlinePlus Medical Encyclopedia”, Medlineplus.gov, 2020. [Online]. Available: https://medlineplus.gov/ency/article/002224.htm

[2] “Antigens | Boundless Anatomy and Physiology”, Courses.lumenlearning.com. [Online]. Available: https://courses.lumenlearning.com/boundless-ap/chapter/antigens/. 

[3] T. Kambayashi and T. Laufer, “Atypical MHC class II-expressing antigen-presenting cells: can anything replace a dendritic cell?”, Nature Reviews Immunology, vol. 14, no. 11, pp. 719-730, 2014. Available: 10.1038/nri3754 

[4] A. Abbas, A. Lichtman and S. Pillai, Cellular and molecular immunology, 9th ed. Philadelphia: Elsevier, 2018, p. 97.

[5] C. Janeway, Immunobiology 5: the immune system in health and disease, 5th ed. Garland Publishing.

[6] L. Borghesi and C. Milcarek, “From B Cell to Plasma Cell: Regulation of V(D)J Recombination and Antibody Secretion”, Immunologic Research, vol. 36, no. 1-3, pp. 27-32, 2006. Available: 10.1385/ir:36:1:27

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