The HLA nomenclature

There are a number of ways that you may see an HLA antigen written. For example, you may see HLA-DR3, HLA-DR17, HLA-DRB1*03 or HLA-DRB1*0301. These could all refer to the same antigen!

What do they mean?

Firstly, as you know, "HLA" is the name for the genetic system on human chromosome number 6, which is responsible for the presentation of "foreign" peptides to the immune system. H.L.A. stands for "Human Leucocyte Antigen" - a name that has been kept more as a tribute to history than actual function.

The second part -DR - is the name of the specific locus. There are 6 loci to which people normally refer. These are A, B, C, DR, DQ and DP.
The HLA-A, B and C loci produce molecules (antigens) that normally present peptides of viral origin and are expressed on all nucleated cells. The HLA-A, B, C antigens are termed Class I.
The HLA-DR, DQ and DP loci produce antigens that normally present peptides which have been broken down from bacterial or other protiens that have been engulfed by the cell in a process of immune surveilance. They are only expressed on cells actively involved in the immune response, eg B lymphocytes monocytes and activated T lymphocytes. The HLA-DR, DQ and DP antigens are termed Class II.
There are other Class I loci besides A, B and C and there are other Class II loci besides DR, DQ and DP. However, these loci are not normally tested for and there significance is not entirely clear.

The third part - the number, eg 3, 17, 03, 0301, refers to the actual antigen at the locus. For example, the DNA in the gene region that we call the HLA-DR locus can be different from person to person. This difference will result in a different type HLA-DR molecule. These different types of HLA-DR molecules are given names, such as DR17. Actually, HLA-DR17 is the old way of writing this antigen - based on using antibodies that react to the antigens on the cells.
Now we can look directly at the DNA and therefore the accuracy is much greater. The problem is that now we can see a lot more variation between the different antigens and so we need a different way of writing them!

So, when we look at the antigens above :-
HLA-DR3 is the broadest description of the antigen. It is the name for a specific group of antigens.
The DR3 group can be divided into HLA-DR17 and HLA-DR18 by using antibodies (serology).
When we look at this antigen at the DNA level we call the DR locus DRB1 (because there are others termed A and B2,B3,etc) and the antigen 03 (for the general antigen) and 01 for the specific variant of the 03. So, HLA-DR17 is now called HLA-DRB1*0301.

This is similar for other antigens in the system, at either HLA Class II or Class I. eg HLA-B60 (HLA-B*4001 molecularly).

How many HLA loci are there?

The currently recognised (Feb 2003) alleles are given below. Notice that HLA-DRB1 is the normal DR locus, the old DRw52 is now DRB3 and DRw53 is now DRB4 :-

 

The common Australian HLA antigens
and their molecular diversity.

The number of alleles that can now be recognised by molecular techniques is huge and is being increased rapidly. The following tables will help to demonstrate the antigens with the greatest diversity and to show the most frequent molecular variants in Australia.

Go to Table for HLA-A, HLA-B, HLA-C, HLA-DR

HLA-A (the more frequent antigens only)

* The number of variants is approximate, as there will be more reported regularly

HLA-B (the more frequent antigens only)

* The number of variants is approximate, as there will be more reported regularly

HLA-C (the more frequent antigens only)

* The number of variants is approximate, as there will be more reported regularly

HLA-DR (the more frequent antigens only)

* The number of variants is approximate, as there will be more reported regularly