HLA system

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Related to HLA system: human leukocyte antigen

HLA (Human Leucocyte A) system

a major HISTOCOMPATABILITY complex of four genes (perhaps five) called HLA-A, HLA-B, HLA-C and HLA-D, with the D locus nearest to the centromere on the shorter arm of chromosome 6. Each gene has up to 35 alleles, the particular combination of alleles of the four genes on a chromosome being called the haplotype. Since humans are diploid organisms we have two haplotypes, these being determined by testing the individual's white blood cells for the specific HLA antigens.

Although these large numbers of alleles would appear to make the system a complex one in terms of possible combinations in each individual, in fact the situation is simpler than it seems. The four loci within the HLA system are so tightly linked together that there is very little CROSSING OVER between them. Thus each haplotype tends to be passed onto an offspring as a block rather than as four individual genes. Given no recombination between the four genes, four rearrangements would be expected to occur in the progeny of a mating. Thus any child of a cross has a one-in-four chance of inheriting precisely the same HLA combination as another sibling. Since the success of organ transplantation depends upon a close match of HLA alleles (even one allele difference can cause the foreign organ to be rejected), the chance of matching HLA types is highest within closely related individuals.

Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005
References in periodicals archive ?
In the HLA system, haplotype is the linkage of particular alleles at distant loci that occur as a group on a parental chromosome.
The naming of new HLA genes, allele sequences, and their quality control is the responsibility of the WHO Nomenclature Committee for Factors of the HLA System. The committee meets regularly to discuss issues of nomenclature and has published 19 major reports documenting the HLA antigens and, more recently, the genes and alleles.
Issues of cost, numbers of samples processed, and simplicity are all relevant and important, but the satisfaction of certain metrics is the top priority because of the ever-evolving complexity of the HLA system. These key metrics, including sample, locus, and allele balance as well as uniformity of coverage, are described in the Analytic Systems section below.
HLA system) and those that are specific to platelets, such as the human platelet antigen (HPA) system.
HLA-A, HLA-C, and HLA-B are members of the HLA system. CXCR6 is related to chemokine receptors.
Thus the autoimmune mechanisms involving the HLA system may provide connections between PsA and Dupuytren's disease.
Forensics started advancing with advancements in the field of genetics where HLA system and Restriction Fragment Length Polymorphisms (RFLPs) opened new ways for investigation.
Basanta, "Association of dengue hemorrhagic fever with the HLA system," Haematologia, vol.
Among the antigens of HLA system HLAA3, HLA-B8, HLA-Cw6 prevailed; group II (36 patients) were characterized by eruptions in the area of large skin folds (intertrigo-like form), among which the immunologic disorders and significant increase in TNF-alpha were most important.
The HLA system: immunobiology, HLA typing, antibody screening and crossmatching techniques.