<unk>  region of Chromosome 6 The<unk>  <unk>  system or complex is a complex of genes on chromosome 6 in<unk> s which encode cell-surface proteins responsible for the regulation of the immune system. The<unk>  system is also known as the<unk>  version of the major histocompatibility complex (MHC) found in many animals. Mutations in<unk>  genes may be linked to autoimmune disease such as type I diabetes, and celiac disease. The<unk>  gene complex resides on a 3 Mbp stretch within chromosome 6, p-arm at 21.3.<unk>  genes are highly polymorphic, which means that they have many different alleles, allowing them to fine-tune the adaptive immune system. The proteins encoded by certain genes are also known as antigens, as a result of their historic discovery as factors in organ transplants.<unk> s corresponding to MHC class I (A, B, and C), all of which are the<unk>  Class1 group, present peptides from inside the cell. For example, if the cell is infected by a virus, the<unk>  system brings fragments of the virus to the surface of the cell so that the cell can be destroyed by the immune system. These peptides are produced from digested proteins that are broken down in the proteasomes. In general, these particular peptides are small polymers, of about 8-10 amino acids in length. Foreign antigens presented by MHC class I attract T-lymphocytes called killer T-cells (also referred to as CD8-positive or cytotoxic T-cells) that destroy cells. Some new work has proposed that antigens longer than 10 amino acids, 11-14 amino acids, can be presented on MHC I eliciting a cytotoxic T cell response. MHC class I proteins associate with β2-microglobulin, which unlike the<unk>  proteins is encoded by a gene on chromosome 15.<unk> s corresponding to MHC class II (DP, DM, DO, DQ, and DR) present antigens from outside of the cell to T-lymphocytes. These particular antigens stimulate the multiplication of T-helper cells (also called CD4-positive T cells), which in turn stimulate antibody-producing B-cells to produce antibodies to that specific antigen. Self-antigens are suppressed by regulatory T cells. Predicting which (fragments of) antigens will be presented to the immune system by a certain<unk>  type is difficult, but the technology involved is improving.<unk> s corresponding to MHC class III encode components of the complement system.<unk> s have other roles. They are important in disease defense. They are the major cause of organ transplant rejections. They may protect against or fail to protect (if down-regulated by an infection) against cancers.<unk>  may also be related to people's perception of the odor of other people, and may be involved in mate selection, as at least one study found a lower-than-expected rate of<unk>  similarity between spouses in an isolated community. Aside from the genes encoding the six major antigen-presenting proteins, there are many other genes, many involved in immune function, located on the<unk>  complex. Diversity of<unk> s in the<unk>  population is one aspect of disease defense, and, as a result, the chance of two unrelated individuals with identical<unk>  molecules on all loci is extremely low.<unk>  genes have historically been identified as a result of the ability to successfully transplant organs between<unk> -similar individuals.
Human leukocyte antigen
Hh blood group
Anton blood group antigen
Rh blood group system
Blood type
Lan blood group system
Isoantibodies
Human blood group systems