Antigen
Also, an antigen is a molecule that binds to Ag-specific receptors, but cannot necessarily induce an immune response in the body by itself. Antigens are usually proteins, peptides (amino acid chains) and polysaccharides (chains of monosaccharides/simple sugars) but lipids and nucleic acids become antigens only when combined with proteins and polysaccharides. In general, saccharides and lipids (as opposed to peptides) qualify as antigens but not as immunogens since they cannot elicit an immune response on their own. Furthermore, for a peptide to induce an immune response (activation of T-cells by antigen-presenting cells) it must be a large enough size, since peptides too small will also not elicit an immune response.
Cancer/testis antigen family 45, member a5
Cancer/testis antigen family 45, member A5 is a protein in humans that is encoded by the CT45A5 gene.
This gene represents one of a cluster of six similar genes located on the q arm of chromosome X. The genes in this cluster encode members of the cancer/testis (CT) family of antigens, and are distinct from other CT antigens. These antigens are thought to be novel therapeutic targets for human cancers. Alternative splicing results in multiple transcript variants. A related pseudogene has been identified on chromosome 5. [provided by RefSeq, May 2010].