The source of HLA molecules on platelets: Does platelets adsorb soluble HLA molecules from their environment?

Background: The origin and function of human leukocyte antigen (HLA) class I molecules on platelets are still highly arguable. Given the differences in the results of the previous studies in this regard, the lack of research in recent years, and the clinical importance of HLA class I molecules, the absorption capacity of platelets for soluble HLA class I molecules was studied in this investigation. Materials and Methods: In this experimental study, HLA-A2 antigen was purified from a B cell precursor leukemia cell line (Nalm-6) by cell membrane protein solubilization and usage of HLA-A2 affinity column. Platelet concentrates (PCs) were received from Tehran Blood Transfusion Center. Eighteen bags of HLA-A2-negative PCs were prepared randomly and treated with various concentrations of the purified HLA antigen (100, 500, and 1000 ng/ml) for 48 to 72 hours. Subsequently, the HLA-A2 levels were evaluated on platelets by flow cytometery technique. Data were evaluated using repeated measure ANOVA.P-values less than 0.05 were considered significant. Results: The results of this study showed that the purified protein was an HLA molecule (HLA-A2).  After the treatment of platelets and HLA molecules, platelets inability was shown for the attracting of HLA molecules. This finding was true in both media of RPMI and plasma. The differences between the case (HLA-treated platelets) and control (untreated platelets) were not significant (p-values> 0.05). Conclusion: Platelets were unable to significantly adsorb exogenous HLA antigens from their environment. Further studies are needed to unravel the nature and origin of HLA molecules on platelets.