These foreign substances are also known as Antigens.
An antigen in immunology is a molecule, molecular structure, foreign particle, pollen grain, or other foreign substance that can attach to a particular antibody or T-cell receptor.
An immunological reaction may be brought on by the presence of antigens in the body. Initially, an agent that produces antibodies was referred to as an antigen. Proteins, peptides, polysaccharides, lipids, and nucleic acids can all serve as antigens.
Antigen receptors, such as antibodies and T-cell receptors, are responsible for recognizing antigens. Immune system cells produce a variety of antigen receptors, giving each cell a specificity for a single antigen.
Only lymphocytes that are able to detect an antigen are activated and enlarged after being exposed to it, a process known as clonal selection.
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