HLA typing- The human leukocyte antigen (HLA) test, also known as HLA typing or tissue typing, identifies antigens on the white blood cells (WBCs) that determine tissue compatibility for organ transplantation (that is, histocompatibility testing). There are six loci on chromosome 6, where the genes that produce HLA antigens are inherited: HLA-A, HLA-B, HLA-C, HLA-DR, HLA-DQ, and HLA-DP. Unlike most blood group antigens, which are inherited as products of two alleles (types of gene that occupy the same site on a chromosome), many different alleles can be inherited at each of the HLA loci. These are defined by antibodies (antisera) that recognize specific HLA antigens, or by DNA probes that recognize the HLA allele. Using specific antibodies, 26 HLA-A alleles, 59 HLA-B alleles, 10 HLA-C alleles, 26 HLA-D alleles, 22 HLA-DR alleles, nine HLA-DQ alleles, and six HLA-DP alleles can be recognized. This high degree of genetic variability (polymorphism) makes finding compatible organs more difficult than finding compatible blood for transfusion . Purpose
HLA typing, along with ABO (blood type) grouping, is used to provide evidence of tissue compatibility. The HLA antigens expressed on the surface of the lymphocytes of the recipient are matched against those from various donors. Human leukocyte antigen typing is performed for kidney, bone marrow, liver, pancreas, and heart transplants. The probability that a transplant will be successful increases with the number of identical HLA antigens. Graft rejection occurs when the immune cells (T-lymphocytes) of the recipient recognize specific HLA antigens on the donor's organ as foreign. The T-lymphocytes initiate a cellular immune response that result in graft rejection. Alternatively, T-lymphocytes present in the grafted tissue may recognize the host tissues as foreign and produce a cell-mediated immune response against the recipient. This is called graft versus host disease (GVHD), and it can lead to life-threatening...
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