The<unk>  <unk>  is a protein that in humans is encoded by the<unk>  gene. It is a 13kb gene on chromosome 21q22.3 that has 545 amino acids.<unk>  is a transcription factor expressed in the medulla (inner part) of the thymus. It is part of the mechanism which eliminates self-reactive T cells that would cause<unk>  disease. It exposes T cells to normal, healthy proteins from all parts of the body, and T cells that react to those proteins are destroyed. Each T cell recognizes a specific antigen when it is presented in complex with a major histocompatibility complex (MHC) molecule by an antigen presenting cell. This recognition is accomplished by the T cell receptors expressed on the cell surface. T cells receptors are generated by randomly shuffled gene segments which results in a highly diverse population of T cells - each with a unique antigen specificity. Subsequently, T cells with receptors that recognize the body's own proteins need to be eliminated while still in the thymus. Through the action of<unk> , medullary thymic epithelial cells (mTEC) express major proteins from elsewhere in the body (so called "tissue-restricted antigens" - TRA) and T cells that respond to those proteins are eliminated through cell death (apoptosis). Thus<unk>  drives negative selection of self-recognizing T cells. When<unk>  is defective, T cells that recognize antigens normally produced by the body can exit the thymus and enter circulation. This can result in a variety of<unk>  diseases. The gene was first reported by two independent research groups Aaltonen et al. and Nagamine et al. in 1997 who were able to isolate and clone the gene from human chromosome 21q22.3. Their work was able to show that mutations in the<unk>  gene are responsible for the pathogenesis of<unk>  polyglandular syndrome type I. More insight into the<unk>  protein was later provided by Heino et al. in 2000. They showed that<unk>  protein is mainly expressed in the thymic medullary epithelial cells using immunohistochemistry.
Autoimmune regulator
Inflammatory cytokine
Lymphokine
Tumor antigen
Cytokine
Bacterial adhesin
Autoantibody
Microantibody