An antigen is a substance that stimulates the body's immune system to produce antibodies, but it is a very broad concept. An antigen can be either a single protein or a whole bacterium. What are the types and properties of antigens?

Antigenis a substance that, when introduced into the body, causes an immune reaction, which consists in the proliferation of lymphocytes and the formation of specific antibodies.

Antigens have various chemical structures - they can be carbohydrates, proteins, lipids, and even nucleic acids.

They have properties such as immunogenicity, i.e. the ability to induce a specific immune response against each other, and antigenicity, i.e. the ability to bind specifically with immunoglobulins and T-lymphocyte receptors.

Continuous and discontinuous antigens

Antigens can be divided into continuous and discontinuous. In the case of continuous antigens, the amino acids of the protein antigen that contact the antibody are contained in one segment of the protein chain.

However, in the case of discontinuous antigens, the amino acids of the protein antigen are spaced apart in the protein chain.

Low and high molecular weight antigens

Due to the size of the molecule, antigens can be divided into small and large molecules. Within the latter, there may be many fragments that are bound by antibodies.

They are called epitopes or antigenic determinants.

They are the smallest unit of antigen that can be recognized by an antibody or cell receptor. Moreover, they can be bound by antibodies of identical or different specificity.

They can trigger both weak and strong immune responses depending on age, he alth, and genetic makeup.

Thymus-dependent and thymic-dependent antigens

Among the antigens, there are also thymic-dependent and thymic-dependent antigens. In response to thymic-dependent B antigens, they require help from T helper lymphocytes to produce antibodies.

In contrast, the response to thymic-non-dependent antigens does not require assistance from T lymphocytes to produce antibodies.

It is worth mentioning here that the larger the antigen molecule, the easier it is to induce the production of antibodies against it. Likewise, the less soluble forms of the antigen induce a much stronger immune response than the soluble forms.

Interestingly, low molecular weight particles are only able to effectively induce the production of antibodies when they become conjugated or spontaneously bind to larger molecules.

Hapteny

There are also antigens that only have the ability to bind specifically to immunoglobulins and T-cell receptors.

These are called haptens and are very small molecules - the size of single antigenic determinants.

The ability to induce a specific immune response against each other (producing antibodies), i.e. they gain immunogenicity only after joining with a larger molecule (carrier), which may be, for example, a protein.

In this situation, B lymphocytes in response to the hapten connected to the carrier recognize the hapten, while the helper cell recognize the protein carrier.

Category:

Immune system