An antigen is an agent located on the foreign cells, which the immune system recognizes.
It is an immunogenic portion present on the foreign cell or substance. These antigens are also present in cancer cells.
When the body recognizes them, it releases antibodies that help destroy those foreign or cancer cells.
To combat that foreign cell with antigen, our body’s immune system produces antibodies.
Differences between antigen and antibody
| Sl.No | Properties | Antigen | Antibody |
|---|---|---|---|
| 1 | Name | Anti – Against Gen – Generate/ formation | Anti – Against Body-Against the body |
| 2 | Other names | Antigens are called Immunogens. | Antibodies are also called immunoglobulins (Igs). |
| 3 | Symbols | The “Ag” symbol can represent the antigen. | The antibody can be represented by the “Ab” symbol. |
| 4 | Processing | The antigen will be processed by the Macrophages, Dendritic cells, and B-cells of Antigen Processing cells (APC) | The Plasma and Memory B-cells will process the Antibody. |
| 5 | Composition | Antigens are mostly made of proteins but also contain carbohydrates, lipids, or nucleic acids. | Antibodies are made up of only proteins like glycoprotein, lipoprotein, etc. |
| 6 | Key part in structure | An antigen contains the epitope region. It is the region that attaches to the antibodies. | Antibody contains a paratope region. It is a variable region that specifically binds to an epitope. |
| 7 | Role | The antigen plays a role in causing disease or evoking an allergic reaction. | Antibody plays a role in the nullification of pathogens or harmful substances. They precipitate the antigenic substance, lyse it, or and lead to phagocytosis |
| 8 | Size | The antigen Size varies from one to another; the greater the size of the molecule, the higher is its antigenicity. | The size of immunoglobulin is variable according to the type of antibody. |
| 9 | Structural difference | The structure of the antigen shows great complexity. | The structure of all classes of immunoglobulins is Y-shaped. |
| 10 | Specificity | The specificity of the antigen depends upon its epitope. | The specificity of the antibody depends on its paratope. |
| 11 | Foreignness | An antigen from the outside environment is highly antigenic. So it is a foreign substance to the body. | Our body’s immune system produces the antibody. |
| 12 | Types | Antigens are grouped into two divisions 1) Foreign Antigens: These are also called Heteroantigens. These antigens present in bacteria, viruses, snake venom, etc. 2) Self Antigens: These are also called autoantigens; these antigens are present within the body and lead to autoimmune disorders. | Antibodies are divided into 5 different types. 1) Immunoglobulin G: The most important of all the antibodies. It is present in the bloodstream and other body fluids. The important function is it can cross the placenta. 2) Immunoglobulin A: It plays an important role in neutralizing bacteria and viruses. It is widely present in respiratory secretions, saliva, tears, etc. 3) Immunoglobulin M: The function of the IgM is the same as IgG, but it cannot cross the placenta. It is the largest-sized antibody. 4) Immunoglobulin E: It is a secondary antibody. It helps to diagnose allergically- reaction and diseases. 5) Immunoglobulin D: It is also a secondary antibody. They help activate the B cell for the defense mechanism. |
| 13 | Prevalence | The antigens are found on bacteria, fungi, viruses, and all different types of cells and biological substances. | The antibodies are produced only by the lymphocytes |
| 14 | Importance | The antigens help to determine the type of microbe or substance entered into the body. | The antibodies are more important to prevent diseases, kill pathogens, and overcome infections. |
| 15 | Features | There are three specific features being 1) Exogenous 2) Endogenous, and 3) Autoantigens. | 1) Specificity. 2) Diversity. 3) Immunological memory. 4) Immune tolerance. |
| 16 | Functions | The function of the antigens is to trigger the production of the antibodies. | 1) They activate the complement system to destroy the pathogens. 2) Promotes the phagocytosis of foreign substances by neutrophils and macrophages |