Human leucocyte antigens

Human leucocyte antigens (HLA) are polymorphisms in cell surface molecules that distinguish 'self' from 'non-self'. They may also be involved in the pathogenesis of certain autoimmune and infectious diseases.

There are two classes of HLA molecules:

  • HLA class I antigens (A, B and C) are expressed on the majority of tissues and cells including T and B lymphocytes, granulocytes and platelets, and
  • HLA class II antigens (DR, DQ, DPA and DPB) are constitutively expressed on B lymphocytes, monocytes and dendritic cells but can also be detected on activated T lymphocytes and activated granulocytes. It’s not clear whether they’re also present on activated platelets.

Although their main role is to present antigens to T cells, HLA antigens can also be recognised as foreign by the host T cells. People exposed to non-self antigens through pregnancy, transfusion or transplantation, may become alloimmunised and develop antibodies directed against these HLA antigens.

 

HLA-matched platelets

Platelet refractoriness is the failure to achieve satisfactory responses to platelet transfusions from random donors. HLA antibodies are implicated in approximately 20% of cases of platelet refractoriness.

HLA-matched platelets can be used in patients with platelet refractoriness through consultation with a Lifeblood Transfusion Medicine Specialist for the following indications:

  • congenital platelet function disorders such as Bernard-Soulier syndrome, Glanzmann thrombasthenia or other congenital platelet disorders where development of HLA alloantibodies may make future platelet support very difficult
  • patients who are to undergo stem cell transplantation using stem cells from a donor who is not a full HLA match and where development of HLA antibodies could result in an adverse transfusion outcome, and
  • patients who are refractory to random platelet transfusions due to the presence of HLA alloimmunisation.
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