The Human Leukocyte Antigen (HLA) system is a group of genes which have an important function in the human immune system. It plays an important role in many clinical settings such as disease susceptibility, blood transfusion, hematopoietic stem cell and solid organ transplantation.
Two main classes of HLA antigens are recognised: HLA class I and HLA class II. HLA class I antigens (A, B, and C in humans) render each cell recognisable as “self,” whereas HLA class II antigens (DR, DP, and DQ in humans) stimulate the immune system. Both have been implicated in the rejection of transplanted organs. Each individual has a unique set of these antigens, half inherited from each parent, and their typing becomes important before organ transplantation. Typing is also used to identify markers for specific diseases, such as HLA B27, which is known to be closely associated with conditions such as ankylosing spondylitis.
The diversity of HLA molecules is the result of nucleotide substitutions at exon(s) and or intron(s) sequences. These substitutions can give rise to amino acid differences that may have impact on peptide presentation or interaction with the T-cell receptor. Furthermore, the HLA region is known to be associated with more than 100 multifactorial, complex diseases mainly of inflammatory and autoimmune pathogenesis.