Types of Antigens
Antigens can be classified based on the following categories;
Based on their Immunogenicity
- Immunogen: These are complete antigens that are capable of induction immunogenic response on their own like bacteria, viruses, etc.
- Haptens: These are incomplete antigens that on their own are incapable of inducing an immune response but can bind with the antibody-like urushiol toxin of poison ivy, penicillin drug as an allergen, etc.
- Autoantigens: Sometimes our body fails to determine certain self-proteins as our own and causes immunogenic responses against them like sperm protein, kidney protein, etc.
- Allo-antigen and Iso-antigen: These are individual-specific antigens that are different from person to person like ABO and Rh antigen of blood cells.
- Heterophilic antigens: When an antigen stimulates an antibody production but those antibodies can even bind with other antigens. These are also called cross-reacting antigens; antibodies produced for the bacteria Streptococcus pyogens can even act against heart muscle proteins.
- Super antigen: The antigens that have the capability to stimulate the production of a large fraction of antibody cells like shock toxins, pyrogenic exotoxins, etc.
Based on their Origin
- Exogenous antigens: The antigens that originate outside the host’s body and then enters the body causing immunogenic response like pollen grains, bacteria, virus, etc.
- Endogenous antigens: The antigens that are produced inside own body like own cells, fragments or compounds produced during cellular metabolism, components produced by the body during any infection, etc.
- Tumor Antigen or Neoantigens: The antigens present on the surface of the tumor cells that stimulate the immune response in the body like MHC-I and MHC-II molecules.
- Native Antigens: Those antigens that are not yet processed by antigen-identifying cells like APC cells due to which they cannot properly induce a full-blown immune response in the body.
What is an Antigen?
Antigen is a substance that can trigger an immune response in the body. It is typically a foreign substance, such as a microorganism, a toxin, or a particle, that the immune system recognizes as being “non-self” and potentially harmful. When the immune system encounters an antigen, it produces specific proteins called antibodies that can recognize and neutralize the antigen, or stimulate other immune cells to attack and destroy it
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