Substances that help the body identify tissue as its own or as foreign. Histocompatibility antigens also help determine whether tissue or organ transplants will be accepted or rejected. Histocompatibility means “tissue compatibility.” If a tissue donor and recipient are histocompatible, as is the case with identical twins, a transplanted organ or tissue will be accepted easily. However, if donor and recipient are not histocompatible, transplants may be rejected by the recipient’s immune system because they are identified as foreign and dangerous.
Human leukocyte antigens (HLAs), proteins dispersed within bodily tissues, exhibiting remarkable individual specificity for nearly every person.
Histocompatibility antigens are a collection of proteins that play a crucial role in the immune system. These specific types of antigens are found on every cell within the body and are crucial for the immunological function of killer T cells, which aid in the body’s defense against diseases. The antigens serve as a guide, allowing the killer T cells to differentiate between the body’s own cells and foreign cells, subsequently eliminating any abnormal or foreign cells.
The primary group of histocompatibility antigens is the Human Leukocyte Antigen (HLA) system, which comprises several antigen series. Six different genes are known within this system: HLA-A, HLA-B, HLA-C, HLA-DP, HLA-DQ, and HLA-DR. Each of these genes has numerous forms, or alleles. For instance, HLA-B has over 40 numbered alleles. A person’s tissue type, which refers to the specific set of HLAs present in their body tissues, is unique, with the exception of identical twins who share the exact same set of HLAs.
HLA analysis has several practical uses. By comparing HLA types, it can be determined whether two individuals are related, which has applications in paternity testing. The HLA system also aids in tissue-typing to ensure a match between recipient and donor tissues before a transplant operation. Certain HLA types are seen more often in individuals with specific diseases. For instance, HLA-B27 is linked with various forms of arthritis, notably ankylosing spondylitis, while HLA-DR2 and a certain HLA-DQ type are associated with narcolepsy. HLA testing can assist in confirming the diagnosis in someone suspected to have one of these conditions.