الفهرس 
Aim of the workOnly 14 pages are availabe for public view
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Abstract
The human leukocyte antigen (HLA) loci of the human major histocompatibility complex (MHC) located on the short arm of human chromosome 6 encode two distinct classes of highly polymorphic cell surface molecules that bind and present processed antigens in the form of peptides to T Lymphocytes. This presentation step is crucial in initiating both cellular and humoral immune responses; consequently these molecules play a central role in the regulation of the immune system, as well as in susceptibility to auto¬immune disorder (Marsh, 1998). The class I molecules, HLA-A, HLA-B, and HLA-C are found on most nucleated cells. They are cell surface glycoproteins that bind and present processed peptides derived from endogenously synthesized proteins (viral and tumour peptides) to CDS T cells. As of the 1998 WHO sequence, update there were 107 HLA-A alleles, 240 HLA-B alleles and 67 HLA-C alleles, this variability is localized primarily to exons 2 and 3, which encode the amino terminal extracellular domains that function as the peptide binding site(Marsh, 1998).