Antigen vs Antibody- Definition and 12 Major Differences

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Differences between antigen and antibody

Antibodies are produced by the immune system in response to antigens (material perceived as foreign). The antibody response to a particular antigen is highly specific and often involves a physical association between the two molecules. This association is governed by biochemical and molecular forces. The reaction between antigens (Ags) and antibodies (Abs) involves complementary binding sites on the Ab and on the Ag molecules. Some of the differences between antigen and antibody are as follows:

Differences between antigen and antibody

Some of the differences are:

S.N.

Characteristics

Antigen

Antibody

1

Molecule Type

 Usually, proteins may also be polysaccharides, lipids or nucleic acids.

Proteins

2

Definition

 These are substances that provoke an immune response.

These are Glycoproteins that are secreted by immune cells (plasma cells) in response to a foreign substance (antigen).

3

Effect

 Cause disease or allergic reactions.

Protect the system by lysis of antigenic material.

4

Origin

 Within the body or externally.

Within the body.

5

Parts

 Highly variable with different structural conformations and is usually composed of different epitopes. Composed of three main parts:

-Two light chains

-Two heavy chains

-Four polypeptides

6

 Prevalence Exists in all types of cells; mostly found in viruses, bacteria, and fungi. Only present in some types of cells.

7

Synonyms

Immunogens

Immunoglobulins

8

Specific binding site

Epitope

Paratope

9

Complexity

Medium; exists due to random mutations in the cell’s gene.

Very High; Complex chemical that bonds to a very specific Antigen.

10

Source

Usually from a foreign substance (viruses, and bacterial and fungal toxins).

 Naturally produced by the body (B lymphocytes or B cells).

11

 Kinds There are three basic kinds of antigens (Exogenous, Endogenous, and Autoantigens)

There are five basic kinds of antibodies (IgG, IgM, IgA, IgE, and IgD).

12

 Examples Exogenous antigens: bacteria, viruses, fungi, etc.

Endogenous antigens: Blood group antigens, HLA (Histocompatibility Leukocyte antigens), etc.

Autoantigens: Nucleoproteins, Nucleic acids, etc.

Breast milk, tears, saliva, sweat, and mucus.

Differences between antigen and antibody

About Author

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Sagar Aryal, PhD

Dr. Sagar Aryal is a microbiologist, researcher, and science communicator from Nepal. He is also co-founder and Research Head of the Department of Natural Products at the Kathmandu Research Institute for Biological Sciences (KRIBS), where he leads research on natural product discovery and microbial biodiversity. Dr. Aryal earned his Ph.D. in Microbiology from Tribhuvan University, Kathmandu, Nepal, in 2025, supported by a DAAD Research Grant and a University Grants Commission (UGC) Nepal Ph.D. Fellowship. His research interests include Actinomycetes, Myxobacteria, microbial taxonomy, and natural products, particularly the discovery of bioactive compounds with potential pharmaceutical applications. He isolated and identified Nocardia nepalensis, a novel bacterial species from Nepal, contributing to understanding microbial diversity in the region. Dr. Aryal has published more than 16 research articles in international journals and contributed three book chapters to established academic publications. He has presented scientific research findings and developed international research collaborations through visits to more than 18 countries across Asia, Europe, North America, and Oceania. From 2023 to 2025, he served as the American Society for Microbiology (ASM) Young Ambassador to Nepal. Since December 2025, he has served as an Editorial Board Member of Scientific Reports, a Nature Portfolio journal. In recognition of his scientific contributions, Dr. Aryal received the NAST Science and Technology Youth Award 2025 from the Nepal Academy of Science and Technology. He previously received the Frs. Locke and Stiller Research Award (LSRA) for the 2017-2018 cycle from St. Xavier's College, Kathmandu, and a Nepal Academy of Science and Technology (NAST) Research Grant for 2017-2018. Alongside his scientific career, Dr. Aryal has more than 15 years of experience in blogging, content writing, and search engine optimization (SEO).