Human Leukocyte Antigen

The human leukocyte antigen system ( HLA system, HL - antigens, Eng. Human Leukocyte Antigen ) is a group of human genes that are central to the function of the immune system. The system also comes under the name of the major histocompatibility complex (MHC of Engl. Major Histocompatibility Complex) in all vertebrates. In humans, the MHC is called HLA system. Other synonyms are histo - compatibility antigen and transplantation antigen.

Genetics

The genes for all HLA proteins with the exception of β - microglobulin (chromosome 15 ) are found approximately in the middle of the short ( p ) arm of chromosome 6 and can be topographically divided into two classes:

  • Class I antigens, (A, B & C)
  • Class II antigens (DR, DP and DQ)

Nomenclature

The name of an HLA antigen is made up as follows from:

  • The abbreviation " HLA "
  • The letter designating the isotype, the locus (e.g., HLA -B)
  • The (often omitted ) indication of the survey method in brackets (eg (PCR - SSO) or (PCR - SSP) )
  • A (sometimes omitted ) asterisk (*)
  • A group number that identifies the specific antigen variant (e.g. HLA-B27 or HLA-B (PCR - SSO) * 27).
  • A two-digit number that describes the variation of the group (eg, HLA -B * 1501)
  • A two-digit number that identifies a variant with a nucleotide substitution of synonymous (eg, HLA -B * 150101 )
  • A two-digit number indicating the intron variation (eg, HLA -B * 15,010,102 )
  • A letter: N for non- expression, L for weak expression (eg, HLA -B * 15,010,102 N)

Medical importance

HL- antigens are used to determine the histocompatibility, which is important for the success of transplantation. The more similar the HLA types of donor and recipient, the lower the risk of rejection. Since then, however enforces the realization that the importance of the similarity of the HLA markers was overestimated for the success of a transplant. Identical HLA characteristics are found only in identical twins or clones.

Another important significance HL antigens on the HLA- typing. It is based on the finding that many diseases are associated with specific HL- antigens. Thus conclusions can be drawn on disease risk.

Furthermore, performing a HLA Testing of donor and recipient in special cases prior to transfusion of platelet concentrates. For receivers that have received several times in the history of platelets, it can lead to sensitization, so that inappropriate platelets are destroyed quickly. The transfusion of HLA matched platelets may be necessary to even produce an increase in platelet counts.

Heredity

Every person has two HLA markers ( alleles) per locus, a maternal and paternal inherited one. The HLA genes for the various loci are linked as a fixed set ( haplotypes ) inherited.

Example: The father has the genotype A1, 2; B8, 40; DR3, 6 with (for example ) the two haplotypes A (A1, B8, DR3 ) and b (A2, B40, DR6 ). The nut has the genotype A2, 29, B15, 44, DR6, 7 (for example ) the two haplotypes A (A2, B15, DR6 ) and B ( A29, B44, DR7 ). Each child inherits from each parent each one haplotypes. Thus, there are only four possible genotypes for a child:

  • A1, 2; B8, 15; DR3, 6
  • A1, 29, B8, 44, DR3, 7
  • A2, 2; B40, 15; DR6, 6
  • A2, 29; B40, 44; DR6, 7

As a paternity test HLA typing is therefore well suited.

Polymerase chain reaction Cloning Parental testing
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