What makes HLA so complex?
Finding an HLA-matched donor can be difficult because there are so many different HLA antigens, or proteins. There are three different HLA class I antigens: A, B and C. There are several HLA class II antigens but the most commonly tested are: DR and DQ. There are many different antigens within each group; for example there are at least 21 different HLA-A antigens. HLA antigens are named with the letter of the locus followed by a number designation unique for a particular antigen, i.e. A1 or A24. Each person inherits one A, B, C, DR and DQ antigen from each parent. Thus, we have two HLA-A antigens, two HLA-B antigens and so on. In addition, the number of possible combinations of HLA-A with -B and -C and –DR and –DQ makes billions of different HLA types possible.
Finding an HLA-matched donor can be difficult because there are so many different HLA antigens, or proteins. There are 3 different HLA class I antigens: A, B and C. There are several HLA class II antigens but the most commonly tested are: DR and DQ. There are many different antigens within each group; for example there are at least 21 different HLA-A antigens. HLA antigens are named with the letter of the locus followed by a number designation unique for a particular antigen, i.e. A1 or A24. Each person inherits one A, B, C, DR and DQ antigen from each parent. Thus, we have 2 HLA-A antigens, 2 HLA-B antigens and so on. In addition, the number of possible combinations of HLA-A with -B and -C and –DR and –DQ makes billions of different HLA types possible.
