Immunogen is a stimulus that produces a humoral or cell-mediated immune response, whereas antigens are any substance that binds specifically to an antibody or a T-cell receptor.
All immunogens are antigens, but all antigens may not be immunogens, some very small molecules called haptens can bind to antibodies or B-cell receptor but they cannot initiate an immune response. Hapten is a molecule that reacts with specific antibody but is not immunogenic by itself, it can be made immunogenic by conjugation to a suitable carrier.
Many drugs like penicillins are haptens. A hapten is essentially an incomplete antigen. These small molecules can elicit an immune response only when attached to a large carrier such as a protein; the carrier typically does not elicit an immune response by itself.
An epitope, also known as antigenic determinant, is the part of an antigen that is recognized by an antibody, B-cell receptor or T-cell receptor.
Generally an antigen has several or many different epitopes and reacts with many different antibodies, an epitope is approximately five or six amino acids in length. An adjuvant is a pharmacological or immunological agent that modifies the effect of other agents. Directly immunizing most antigens will lead to a poor immune response and rapid removal of the antigen from the body.
To prevent this, the antigen is first combined with an adjuvant, which is a material that helps stimulate and enhance the immune response against the antigen through the creation of a depot effect. Adjuvants can act in various ways in presenting an antigen to the immune system.
They can act as a depot for the antigen, presenting the antigen over a longer period of time, thus maximizing the immune response before the body clears the antigen. Skip to content Immunology News Whenever we refer a pathogen, we may think the entire microbe is responsible for the disease. An antigen is a molecule that can trigger an immune response by acting as an immunogen. It can be either a protein, peptide or polysaccharides.
Lipids and nucleic acids can also serve as antigens when binding to proteins. A particular antigen may contain one or more epitopes, which are the antigen determinants. Antibodies recognize and bind to these epitopes. Furthermore, the immune system produces specific glycoproteins called antibodies in response to epitopes. There are four main types of antigens occur in the body:. Figure 1: Antigens Directly Bind to an Antibody. A hapten is an incomplete antigen which can elicit an immune response only when attached to a large carrier such as a protein.
Hapten carriers are circulating molecules through the body. An adduct refers to the combination of the hapten and the carrier. However, haptens cannot bind to the MHC complex independently; hence, they cannot be presented to the T cells. Urushiol is a well-known hapten found in Ivy.
It serves as a toxin, which causes cell-mediated contact dermatitis. When absorbed, it is oxidized into quinone inside the skin cells. Quinone reacts with skin proteins to form an adduct. Figure 2: Formation of Hapten-Carrier Adduct.
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