An antigen is a molecule capable of inducing an immune response (to produce an antibody) in the host organism. This is the definition of antigen in the discipline of immunology. Antigens are "targeted" by antibodies. Each antibody is specifically produced by the immune system to match an antigen after cells in the immune system come into contact with it. This allows a precise identification or matching of the antigen and the initiation of a tailored response.
The antibody matches with the antigen so that it can bind to it. Considering this, many different antibodies are produced, each could specifically bind to a different antigen while sharing the same basic structure. In most cases, an adapted antibody can only react to and bind one specific antigen. Nevertheless, in some instances, antibodies may cross-react to and bind more than one antigen.
Recently, there is a marked increase in the use of synthetic peptide antigens as immunogens, and this technique is also widely applied for immune research such as tumor immunotherapy. By controlling the presentation of antigen peptides to the immunoregulatory T helper cells, new classes of drugs can be developed to enhance vaccines or to suppress autoimmune disease. These include infusion of vaccines consisting of hapten-modified autologous melanoma cells, poorly characterized tumor lysates, peripheral blood mononuclear cells loaded with tumor antigen peptides plus adjuvants, and the use of melanoma vaccines combined with therapies designed to eliminate pathways and signals that would down-regulate a protective immune response to the vaccine.
Catering to the rising demand for peptide antigens, many companies have expanded their business range to the synthesis of complex antigen peptides, such as glycopeptides or hyperphosphorylation peptides. To conduct this business, one important factor is the designing of peptide antigen.
Although many peptide sequences are immunogenic, not all of them are identically effective in generating antibodies when acting against the target protein. Effective antibody generation depends on several factors that need to be considered at the very first stage of peptides designing.
Mimicking specific parts of the target protein, peptide antigens can provide much flexibility for scientific research. However, most of synthetic peptides are composed of 10AA -25 AA, which are too short to generate a strong immune response without prior conjugation to a carrier protein such as Keyhole Limpet Hemocyanin(KLH), Ovalbumin(OVA) or Thyroglobulin(Tg). Experienced specialists can help with antigen design so as to maximize the chances that the peptide used as antigen can generate sufficient and effective antibody.