A new method was studied for eliminating HLA class I antigens from the surface of platelets without damaging the cells. Platelets were exposed to an acid solution (pH 3.0) to eliminate the antigenicity of HLA class I antigens. The reduction in antigenicities of HLA class I common antigen and individual HLA class I antigens by acid treatment was marked. Patients' sera which contained multispecific HLA antibodies reacted with PBS-treated platelets, but not with acid-treated platelets. No changes were observed in the antigenicities of glycoprotein Ib or glycoprotein IIb/IIIa. The viability of acid-treated platelets was 83%. Ultrastructural investigations revealed no significant difference between the PBS-treated platelets and acid-treated platelets. The platelet function studies showed that the aggregation of acid-treated platelets induced by various agonists was only slightly reduced compared with PBS-treated platelets. We propose that acid-treated platelets are promising for clinical use in patients refractory to platelet transfusions and may be superior to chloroquine-treated platelets for analysis of the specificity of antiplatelet antibodies.
The identification of antibodies to platelet-specific antigens is important for correctly diagnosing neonatal alloimmune thrombocytopenia, posttransfusion purpura and refractoriness due to platelet-specific antibodies. However, the serologic identification of these platelet-specific antibodies is complicated by the presence of anti-HLA antibodies. We examined and compared the diagnostic usefulness of acid-treated and chloroquine-treated platelets for the discrimination of platelet-specific antibodies from anti-HLA antibodies. The viability of acid-treated platelets is 83.4%, which is better than that of chloroquine-treated platelets (52.6%). The antigenicity of HLA class I antigens of acid-treated platelets was significantly reduced compared with that of PBS- or chloroquine-treated platelets. On the other hand, platelet surface glycoprotein Ib and glycoprotein IIb/IIIa, and platelet-specific antigens were stable following acid or chloroquine treatment. Chloroquine-treated platelets were not suitable targets for analysis by immunofluorescence flow cytometry because of nonspecific fluorescence derived from platelet damage. We conclude that acid-treated platelets are more suitable targets than chloroquine-treated platelets for screening for platelet-specific antibodies and also for analyses of the specificity of platelet-specific antibodies.
Although recently published case reports suggest the significance of Jr(a) alloimmunization in the obstetric setting, the involved mechanism still remains unclear. Here we report a case of severe fetal and neonatal anemia associated with anti-Jr(a) alloimmunization, which was successfully managed using Doppler assessment of peak systolic velocity of the fetal middle cerebral artery (MCA-PSV). A Japanese woman with anti-Jr(a) (titer 1024) was referred to our department at 20 weeks' gestation. As fetal MCA-PSV exceeded 1.5 multiple of median, labor was induced and a female neonate of 1998 g was delivered vaginally at 33 weeks and 5 days of gestation. The infant's hematocrit and hemoglobin levels were 25.4% and 82 g/L, respectively, but her total bilirubin level (15 µmol/L; 0.9 mg/dL) and reticulocyte counts (4.5%) were low. During the course, the infant showed no apparent signs of hemolysis. Jr(a) alloimmunization should be recognized as a possible cause of fetal anemia with no direct hemolytic process.
A new method was studied for eliminating HLA class I antigens from the surface of platelets without
damaging the cells. Platelets were exposed to an acid solution (pH 3.0) to eliminate the antigenicity of HLA class I
antigens. The reduction in antigenicities of HLA class I common antigen and individual HLA class I antigens by acid
treatment was marked. Patients’ sera which contained multispecific HLA antibodies reacted with PBS-treated platelets,
but not with acid-treated platelets. No changes were observed in the antigenicities of glycoprotein lb or glycoprotein
IIb/IIIa. The viability of acid-treated platelets was 83%. Ultrastructural investigations revealed no significant difference
between the PBS-treated platelets and acid-treated platelets. The platelet function studies showed that the aggregation of
acid-treated platelets induced by various agonists was only slightly reduced compared with PBS-treated platelets.
We propose that acid-treated platelets are promising for clinical use in patients refractory to platelet transfusions and
may be superior to chloroquine-treated platelets for analysis of the specificity of antiplatelet antibodies.
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