Anti-HPA-1a in a case of post-transfusion purpura: binding to antigen-negative platelets detected by adsorption/elution

Post-transfusion purpura (PTP) is a rare transfusion reaction almost exclusively observed in female patients. Affected patients develop severe immune-mediated thrombocytopenia in the course of a strong anamnestic alloimmune reaction against a platelet-specific antigen. The pathophysiology of thrombocytopenia has remained elusive. Immunological analysis in the HPA-1a-alloimmunized patient described in this report revealed an antibody with features considered typical of PTP: not only was anti-HPA-1a detectable in plasma, but it could also be eluted from the patients' (alloantigen negative) platelets, and anti-HPA-1a could be detected in eluates from both antigen positive and negative test platelets, which had been incubated in the patient's serum. This is in contrast to two sera with HPA-1a alloantibodies obtained from mothers of children with neonatal alloimmmune thrombocytopenia which were strictly HPA-1a specific. It is proposed that alloantibodies with HPA-1a-like specificity explain the patient's immune thrombocytopenia. The technique described in this report is proposed for further investigation, as it might be useful for discrimination of alloantibodes in PTP and alloantibodies of transfused thrombocytopenic patients.