Résumé
BACKGROUND: Platelet refractoriness has been reported to occur in 30-70% of multitransfused patients. This can result by either immune or nonimmune mechanisms. The predominant immune cause of platelet refractoriness is alloimmunization to HLA class I antigens. Recently, acid-treated platelets have been used in a few patients with platelet refractoriness due to HLA alloantibodies. However, the effect of acid-treated platelets has not been consistent. The aim of this study was to evaluate the in vivo survival of acid-treated, HLA-eluted platelets in HLA-immunized rabbits. METHODS: For in vivo survival test, 14 New Zealand White rabbits were studied. Four rabbits were in the nonimmunized control and 10 were immunized by weekly transfusions of human pooled platelets for six weeks. The HLA-immunized group was separated into two groups with transfusion of acid-treated platelets and untreated platelets. The survival of transfused platelets in rabbits with immunization and control group was estimated by a flow cytometer using FITC-labeled anti-CD42a. We also examined the HLA re-expression in acid-treated platelets due to regeneration and adsorption of HLA from human plasma. RESLUTS: The half-life of untreated platelets in nonimmunized rabbits was 11.8 +/- 3.7 hr. The half-life of acid-treated platelets in rabbits with HLA antibodies was 9.5 +/- 5.5 hr and the half-life of untreated platelets in rabbits with HLA antibodies was 5.9 +/- 2.9 hr. The difference between untreated platelets in the nonimmunized control group and acid-treated platelets in rabbits with HLA antibodies was statistically insignificant (p=0.221). Re-expression of HLA-A,B,C by endogenous resynthesis occurred continuously, and after 24 hrs it reached 84% of pre-elution level. Adsorption of HLA antigens from human plasma was completed within four hrs. CONCLUSIONS: Acid-treated, HLA-eluted platelets may be applicable for the patients with refractoriness to platelet transfusion, especially, in case of unavailability of HLA-compatible donors and fatal bleeding such as intracranial hemorrhage and pulmonary hemorrhage. However, the post-transfusion increment of the platelet count could not be maintained over 24 hrs because of the endogenous resynthesis of HLA antigens.