The relevance of HPA-15 antigen expression for anti-HPA-15 antibody detection

Introduction: The HPA‐15 antigen system is characterized by a low antigen expression on platelets. The antibodies against this antigen are implied in fetal/neonatal alloimmune thrombocytopenia (F/NAIT), post‐transfusion purpura, and refractoriness to platelet transfusions. Detection of these antibodies appears to be related to the level of HPA‐15 expression on the platelets used in the monoclonal antibody–specific immobilization of platelet antigen (MAIPA) assay. Methods: We performed genotyping of 300 healthy blood donors for HPA‐15 by TaqMan real‐time PCR technology, and the HPA‐15 antigen expression was investigated in 13 HPA‐15aa and 19 HPA‐15bb individuals. We also investigated the relevance of HPA‐15 antigen expression on donor platelets used in MAIPA for antibody detection in 223 multitransfused hematological patients and 271 women with suspected F/NAIT. Results: In Polish donors, the HPA‐15a allele frequencies were lower than the HPA‐15b (0.480 vs. 0.515). We identified three HPA‐15 expression groups: high (36.7 ± 8.36 MFI – eight cases), medium (19.5 ± 6.2 MFI – 21 cases), and low (6.5 ± 5.9 MFI – three cases). The HPA‐15 expression was stable over time. The HPA‐15aa and HPA‐15bb platelets with high antigen expression were used for anti‐HPA‐15 antibody detection; anti‐HPA‐15 antibodies were detected in 4/223 (1.8%) patients receiving multiple transfusions but in none of the 271 women with suspected F/NAIT. Further examination of the four sera by MAIPA with various platelets revealed the optical density in the assay to be closely related to the level of HPA‐15 antigen expression. Conclusion: Anti‐HPA‐15 antibody detection should be based on carefully selected platelets with high HPA‐15 expression level.