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.
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.