An antigen is a molecule or molecular structure that can cause an immune response. An antigen can be anything from a pollen grain to foreign particulate matter. It triggers an immune response when it binds to a specific antibody or T-cell receptor. The body’s immune response is a natural defense mechanism against foreign bodies.
Exogenous antigens
To be recognized by T cells, exogenous antigens must be transported across the membrane, a process dependent on endocytosis. Unlike particulate substrates, soluble antigens are taken up by separate endocytosis pathways and routed to stable early endosomes. Once there, they undergo proteasomal degradation and peptide loading.
Exogenous antigens can enter the body by ingesting food particles or inhaling air. Once they enter the body, they are processed by APCs to produce fragments that present themselves on cell membranes with MHC class II molecules. These fragments are then recognized by T cells.
Antigens are large biopolymers that have characteristics that activate the immune system. They can be proteins or polysaccharides. They can be found on the surfaces of microbial, viral, or human cells. Antigens are made up of various epitopes, segments of a protein that binds to the body’s cells.
The two major classes of antigens are endogenous and exogenous. The body makes endogenous antigens, while exogenous ones come from the outside. Exogenous antigens are the more common types. They are intracellular or extracellular and are generated by the immune system. These two types of antigens can trigger allergic reactions.
These two classes of antigens are presented by different cell surface molecules called CD1. They are specialized to bind to a specific type of antigen. Antigen-presenting cells express several forms of CD1, one more hydrophobic than the other. The receptors on CD1 are responsible for presenting the antigen to the T cells. Nitric oxide appears to be essential for this process.
Tolerogens
Antigens are substances of various origins containing signs of genetic foreignness that trigger an immune response. These immune responses can be cellular, humoral, or include the induction of immune memory. The properties of an antigen depend on a complex combination of factors, including immunogenicity (the ability to induce an immune response) and specificity (the ability of the immune system to recognize and react to a particular antigen).
Tolerogens are chemicals that can suppress the immune response in an individual. These substances can be accessible or contained within a cell. A complete antigen induces an immune response. An incomplete antigen does not trigger an immune response but may still be immunogenic when bound to a carrier, such as a protein.
Antigens have two main types: monovalent and polyvalent. Monovalent antigens contain only one epitope, while polyvalent antigens have several epitopes. Polymeric antigens have many antigenic determinants and high molecular weight.
Antigens are proteins that can induce a specific immune response in an individual. Their immunogenicity is determined by the number of epitopes that they contain. A full-fledged antigen can interact with various cells and molecules but is usually insoluble.
Tumor antigens
Tumor antigens are abnormal proteins that are produced by a tumor cell. These proteins result from gene mutations. These abnormal proteins can be tumor-specific or tumor-associated. Some examples of tumor-specific antigens are the abnormal products of the ras and p53 genes. Other tumor-specific antigens may result from gene mutations unrelated to the formation of a tumor.
Tumor antigens are molecules expressed on a cancer cell’s surface. They may be released into the bloodstream or remain on the cell’s surface. These molecules are considered antigens because the immune system can recognize them. The immune response to a tumor antigen varies depending on the specific antigen. Often, this response is not enough to kill the cancer cells.
An antitumor immune response aims to stimulate T cells to recognize the overexpressed proteins. To target these proteins, a minimum number of HLA-peptide complexes should be displayed on the surface of a tumor cell. These overexpressed proteins play a role in the growth and survival of cancer cells. Some examples of these overexpressed antigens are WT-1, CEA, and Her-2/neu. Although these proteins may be overexpressed on the surface of a cancer cell, their expression on normal cells also contributes to their immunogenicity.
Tumor antigens can be identified using next-generation sequencing and bioinformatics techniques. These techniques allow for the identification of a tumor’s antigens, which has the potential to lead to more targeted and successful immunotherapy.