Abstract
Alloimmunisation to platelet antigens is not uncommon; a large number of females, having had pregnancies, developed antibodies to Human Leukocyte Antigen (HLA) moieties harboured on their foetuses’ cells (inherited from the father(s)) that may conflict with further pregnancies and transfused Platelet Components occasionally. This is possible since platelets constitutionally express HLA class I molecules (though in copy numbers that consistently differ among individuals). Platelets also express HPA moieties that are variants of naturally expressed adhesion and aggregation molecules; HPA differences between mothers and foetuses and between donors and recipients explain alloimmune conflicts and consequences. Lastly, platelets express ABO blood group antigens, which are rarely immunising, however transfusion mismatches in ABO groups seem to be related to immunisation in other blood and tissue groups. Transfusion also brings residual leukocytes that may also immunise through their copious copy numbers of HLA class I (rarely class II on activated T lymphocytes, B cells, and dendritic cells). In addition, residual red blood cells in platelet concentrates may induce anti-red blood cell allo-antibodies. This short review aims to present the main mechanisms that are commonly reported in alloimmunisation. It also critically endeavours to examine paths to either dampen alloimmunisation occurrences or to prevent them.
Highlights
EA_3064, Faculty of Medicine of Saint-Etienne, University of Lyon, 42023 Saint-Etienne, France; Institut National de la Transfusion Sanguine, 75015 Paris, France
Foreign platelets can be exposed to the body and the immune system in two circumstances: (i) Exposure most commonly occurs during pregnancy where micro-haemorrhage can occur at different times during pregnancy but most often at the onset of placental circulation and during the perinatal period
Red blood cell component transfusion can immunise against Human Leukocyte Antigen (HLA) moieties as a consequence of residual leukocytes that express high levels of HLA class I
Summary
Foreign platelets can be exposed to the body and the immune system in two circumstances:. Red blood cell component transfusion can immunise against HLA moieties as a consequence of residual leukocytes that express high levels of HLA class I molecule, present on platelets. They can be immunised by HLA class I variants (platelets express this set of molecules, in numbers that vary greatly among individuals alongside ABH antigens [25] and always in a smaller number of copies than on leukocytes) [26] They can be immunised by residual red blood cells and antigenic moieties, as minimal amounts of them may be highly immunogenic (RhD for example). Abs to GP1ba can activate platelets to produce sialidases which alter the glycocalyx and expose Galactose residues Such platelets are Bearing in mind that Ab detection tests mainly detect plasma-free, cell unbound, anti-HLA/HPA phagocytosed by certain hepatocytes [36]. Such platelets are phagocytosed by certain hepatocytes [36]
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